Progress 10/01/14 to 09/30/15
Outputs
Target Audience:
Nothing Reported
Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
No Activity per PI
Publications
|
Progress 10/01/13 to 09/30/14
Outputs
Target Audience: The target audience of the entomological and sentinel animal surveillance program that is guiding our predictive modeling work has included decision makers, producers, and stakeholders in commodity groups including the dairy, beef, and sheep industry. Within these groups, the focus has centered on: 1. vector borne diseases of livestock and humans, 2. regulation of animal movement, 3. potential impacts of climate change, and 4. livestock production systems. The goal is to prepare the state and nation for emergence of any disease transmitted by biting Culicoides midges, specifically an exotic and/or virulent strain of bluetongue virus, epizootic hemorrhagic disease virus, African horse sickness virus, or any other related pathogen that might invade the United States. The predictive model we have developed is informed by pertinent and relevant parameter estimates collected in our surveillance program and should identify optimal control strategies that might be utilized in such an event. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? These studies have also allowed us the ability to instruct and train undergraduate, DVM and graduate academic students in field and laboratory research. Most of this work has occurred on dairy farms using a sentinel cattle network, as prescribed by the OIE code. The dairies offered a remarkable ecological situation where animals, vectors, meteorological conditions, and anthropogenic factors can be readily measured and managed for the reporting period. Through successful completion and analysis of results of our surveillance program, we have identified key meteorological, anthropogenic and land use factors influencing BTV infection among cattle housed at intensive dairy farms in California. We have also expanded oursurveillance to incorporate free-ranging livestock species (i.e. beef cattle operations, sheep flocks) to fully define the epidemiology of BTV infection in specific regions of California. We accomplished this objective using beef cattle and sheep as the model of a free-ranging livestock species, which is logical given their availability and ease of handling. This project has provided much needed data on the epidemiology of BTV infection among livestock in California, and the ecological niches required for vector, host, and BTV transmission. Acquisition of this data is pre-requisite to building accurate predictive models, especially in the face of climate change and all of its attendant potential impacts on emergence of arboviral diseases. How have the results been disseminated to communities of interest? The results have been published in peer reviewed journals and presented at a number of meetings including: local woolgrowers, California Cattleman’s Association, dairy industry, California Department of Food and Agriculture (CDFA), the International Society of Vector Ecology (invited), the American Association of Veterinary Laboratory Diagnosticians, United States Animal Health Association, the Institute for Animal Health at Pirbright, United Kingdom (invited), and the World Veterinary Congress in Cape Town, South Africa (invited). What do you plan to do during the next reporting period to accomplish the goals? In order to achieve our goals, we will be expanding our current studies to incorporate viral isolates obtained from sentinel animals to further understand the viral diversity of BTV isolates throughout the state of California. We propose to accomplish this objective using whole genome deep sequencing of contemporary and historic (>30 years) BTV viral isolates. This data will allow us to build upon our ongoing entomological field surveys to investigate the potential role of gene flow amongst field strains of BTV. This project will provide much-needed data linking the epidemiology and viral diversity of BTV by characterizing the sequences of all 10 segments, which is prerequisite to development of logical control strategies in endemic temperate regions. We also wish to expand our current studies to further understand the inter-seasonal BTV transmission cycle and potential overwintering strategy. We propose to accomplish this objective using both field and laboratory studies to identify if BTV overwinters in California through vertical transmission of virus within female C. sonorensis midges. Thus, this data will allow us to build upon our ongoing entomological field surveys to investigate the potential role of transovarial transmission of BTV in vector insects in virus overwintering. This project will provide much-needed data on the epidemiology of BTV by characterizing the inter-seasonal transmission cycle, which is prerequisite to development of logical control strategies in endemic temperate regions The data provided by these studies is essential to the future creation of accurate and predictive models of BTV infection of livestock, especially the objective data relating virus transmission in livestock to vector abundance, BTV infection prevalence and activity. Our studies confirm that anthropogenic factors, and not just meteorological ones, can be important in determining the prevalence of BTV infection of livestock on individual farms in California. Our overall goal is identify the relative importance of individual ecological drivers and specific management practices on vector populations and their relationship to the local and regional prevalence of BTV infection of livestock; however, this can only be fully completed by exploring viral diversity and interseasonal maintenance to gain a better perspective of global epidemiology, especially in application to predictive modeling systems. Incorporating pertinent and contemporary data into our models has been extremely important in making accurate predictions and establishing “what-if” scenarios for the likely effects of potential control measures to mitigate climate or anthropogenic change.
Impacts
What was accomplished under these goals?
Through successful completion and analysis of results of our surveillance program, we have identified meteorological and anthropogenic drivers of BTV infection among cattle housed at intensive dairy farms in California and we recently submitted a proposal to the USDA NIFA AFRI (FY 2014) and NSF EEID programs. The current USDA NIFA AFRI grant has allowed us to continue our targeted surveillance strategy. The development of a one host/one vector ecological (SEIR) model, based on existing surveillance data to inform parameter estimates, has allowed us to direct our field studies to better characterize the ecological drivers of bluetongue virus (BTV) infection of livestock and for predictive modeling of future BTV outbreaks. Recent studies utilizing the combination of sentinel dairy cattle and entomological surveys over a 52-week period have identified several major paradigm shifts in the understanding of both the population dynamics of Culicoides midges and BTV infection within regional zones of California. The Sacramento (northern Central) Valley of California (CA) has a hot Mediterranean climate and a diverse ecological landscape that is impacted extensively by human activities, which include the intensive farming of crops and livestock. Waste-water ponds, marshes, and irrigated fields associated with these agricultural activities provide abundant larval habitats for C. sonorensis midges, in addition to those sites that exist in the natural environment. One study dairy farm had large operational waste-water lagoons, whereas the lagoon on another study farm was drained and remained dry during the study. Recent studies performed at UC Davis utilizing the combination of sentinel dairy cattle and entomological surveys over a 52-week period have identified several major paradigm shifts in the understanding of both the population dynamics of Culicoides and BTV infection within regional zones of California. The Sacramento (northern Central) Valley of California (CA) has a hot Mediterranean climate and a diverse ecological landscape that is impacted extensively by human activities, which include the intensive farming of crops and livestock. Waste-water ponds, marshes, and irrigated fields associated with these agricultural activities provide abundant larval habitats for C. sonorensis midges, in addition to those sites that exist in the natural environment. One study dairy farm had large operational waste-water lagoons, whereas the lagoon on another study farm was drained and remained dry during the study. Spring emergence and seasonal abundance of adult C. sonorensis on both farms coincided with rising vernal temperature. Paradoxically, the abundance of midges on the farm without a functioning waste-water lagoon was increased as compared to abundance on the farm with a waste-water lagoon system, indicating that this infrastructure may not serve as the sole, or even the primary larval habitat. Adult midges disappeared from both farms from late November until May, as determined by collection using conventional EVS traps from dusk to dawn; however, low numbers of parous female midges were detected in traps set during daylight in the inter-seasonal winter period. This latter finding is especially critical as it provides a potential mechanism for the “overwintering” of BTV in temperate regions such as northern CA and northern Europe To further characterize the dynamics of BTV activity in both vector insects and sentinel cattle, we determined BTV infection (using BTV-specific real time reverse transcriptase polymerase chain reaction) among sentinel cattle and vector C.sonorensis midges on the dairy farm where low numbers of females were collected in the winter. The midges had been collected throughout both the seasonal and interseasonal (over-wintering) periods of BTV activity from August 2012 until March 2014. The data confirmed widespread infection of both sentinel cattle and vector midges during the August – November period of seasonal BTV transmission, however BTV infection of parous female midges captured in traps set during daylight hours also was detected in February of both 2013 and 2014, during the interseasonal period of virus activity. The finding of BTV-infected vector midges during mid-winter suggests that BTV may overwinter in northern California by either: 1.survival of female C. sonorensis midges, infected during the prior seasonal period of virus transmission, which entered a quiescence in the fall and reemerged sporadically during the overwintering period; or 2. uninfected female midges emerging during winter from cohorts oviposited in the prior fall and feeding on a BTV-infected animal, although animal surveillance at the time identified no active virus circulation among an extensive cohort of sentinel cattle (Figure 1). The data do not definitively preclude other potential mechanisms of BTV overwintering including the potential for vertical transmission but identify the need for precise understanding of temporal changes in the annual abundance and dispersal of Culicoides midges, in terms of intrinsic (e.g. density dependence) and extrinsic drivers (e.g. climate and hydrology). This is essential for the creation of models to predict BTV infection of livestock and to evaluate sound abatement strategies. Additionally, in light of dramatic recent changes in the global distribution of BTV, a cross-sectional study was conducted to identify regional and local environmental, host, and anthropogenic risk factors associated with BTV seroprevalence among commercial dairy cattle in different ecological regions of California. A serosurvey of adult dairy cattle confirmed that BTV infection is prevalent throughout much of the state, although mean seroprevalence was significantly higher within two regions (Sacramento Valley and Southern California). A conditional autoregressive model was used to model BTV seroprevalence as a function of climatic, landscape, and host variables while accounting for spatial autocorrelation. High temperatures, high percentage cover of irrigated cropland and large herd sizes significantly increased BTV seroprevalence among dairy cattle herds. The analysis suggests that the combination of specific environmental, landscape, and animal host factors can create a favorable ecological niche for recurring annual seasonal transmission of BTV. Both studies highlight the need to further characterize ecological and environmental factors driving BTV infection and Culicoides vectors beyond the dairy infrastructure. We have made substantial progress with this project in collecting field data among dairy farms, necessary to construct predictive models. We have also constructed a reliable surveillance network that can be easily adapted for different livestock systems. Therefore, the final portion of this project is to adapt our current surveillance system to further understand the variability/similarity of endemic viral strains to enhance our current epidemiologic models. As a direct result, these models will be used for the logical development of practical and cost-effective methods to reduce numbers of Culicoides midges on individual farms or within flocks thereby reducing the risk of BTV transmission and other midge transmitted infections of livestock. The use of a comprehensive surveillance system on local dairy farms has allowed us to better assess and understand the natural seasonal transmission of BTV infection among diary cattle. Ultimately, in adapting this tool during the non-seasonal period of transmission will allow us to better predict actual risk of virus transmission to all livestock. Our long-term goal, therefore, is to develop accurate data pertaining to relative vector abundance, attack rates, and BTV prevalence from our field studies, and to utilize this data in developing an improved model for risk estimation.
Publications
- Type:
Books
Status:
Published
Year Published:
2014
Citation:
Maclachlan, N.J. and Mayo, C.E., Smith, B.P. Bluetongue, in Smith, B.P. (Eds). Large Animal Internal Medicine, 5th ed., Elsevier Science Publishing Company, New York, NY
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Mayo, C.E., Mullens, B.A., Reisen, W.K., Osborne, C.J., Gibbs, E.P., Gardner, I.A., MacLachlan, N.J., 2014. Seasonal and Interseasonal Dynamics of Bluetongue Virus Infection of Dairy Cattle and Culicoides sonorensis Midges in Northern California - Implications for Virus Overwintering in Temperate Zones. PLoS One 9, e106975.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Gaudreault, N.N., Mayo, C.E., Jasperson, D.C., Crossley, B.M., Breitmeyer, R.E., Johnson, D.J., Ostlund, E.N., MacLachlan, N.J., Wilson, W.C., 2014. Whole genome sequencing and phylogenetic analysis of Bluetongue virus serotype 2 strains isolated in the Americas including a novel strain from the western United States. J Vet Diagn Invest 26, 553-557.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Osborne, C.J., Mayo, C.E., Mullens, B.A., Maclachlan, N.J., 2014. Estimating Culicoides sonorensis biting midge abundance using digital image analysis. Med Vet Entomol. doi: 10.1111/mve.12060.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Mayo, C.E., Osborne, C.J., Mullens, B.A., Gerry, A.C., Barker, C.M., Gardner, I.A., Reisen, W.K., MacLachlan, N.J., 2014. Seasonal variation and impact of waste-water lagoons as larval habitat on the population dynamics of Culicoides sonorensis midges at two dairy farms in Northern California. PLOS ONE, DOI: 10.1371/journal.pone.0089633.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Maclachlan, N.J., Mayo, C.E., 2013. Potential strategies for control of bluetongue, a globally emerging, Culicoides-transmitted viral disease of ruminant livestock and wildlife. Antiviral Res 99, 79-90.
|
Progress 01/01/13 to 09/30/13
Outputs
Target Audience: The target audience of the entomological and sentinel animal surveillance program (guiding our predictive modeling work) has included decision makers, producers, and stakeholders in commodity groups including the dairy, beef, and sheep industry. Within these groups, the focus has centered on: 1. vector borne diseases of livestock and humans, 2. regulation of animal movement, 3. potential impacts of climate change, and 4. livestock production systems. The goal is to prepare the state and nation for emergence of any disease transmitted by biting Culicoides midges, specifically an exotic and/or virulent strain of bluetongue virus, epizootic hemorrhagic disease virus, African horse sickness virus, or any other related pathogen that might invade the United States. The predictive model we have developed is informed by pertinent and relevant parameter estimates collected in our surveillance program and should identify optimal control strategies that might be utilized in such an event. Changes/Problems: There are no current modifications to the project described. What opportunities for training and professional development has the project provided? These studies have also allowed us the ability to instruct and train undergraduate, DVM and graduate academic students in field and laboratory research. Most of this work has occurred on dairy farms using a sentinel cattle network, as prescribed by the OIE code. The dairies offered a remarkable ecological situation where animals, vectors, meteorological conditions, and anthropogenic factors can be readily measured and managed for the reporting period. Through successful completion and analysis of results of our surveillance program, we have identified key meteorological, anthropogenic and land use factors influencing BTV infection among cattle housed at intensive dairy farms in California. We have also expanded oursurveillance to incorporate free-ranging livestock species (i.e. beef cattle operations, sheep flocks) to fully define the epidemiology of BTV infection in specific regions of California. We accomplished this objective using beef cattle and sheep as the model of a free-ranging livestock species, which is logical given their availability and ease of handling. This project has provided much needed data on the epidemiology of BTV infection among livestock in California, and the ecological niches required for vector, host, and BTV transmission. Acquisition of this data is pre-requisite to building accurate predictive models, especially in the face of climate change and all of its attendant potential impacts on emergence of arboviral diseases. How have the results been disseminated to communities of interest? The results have been published in peer reviewed journals and presented at a number of meetings including: local woolgrowers, California Cattleman’s Association, dairy industry, California Department of Food and Agriculture (CDFA), the International Society of Vector Ecology (invited), the American Association of Veterinary Laboratory Diagnosticians, United States Animal Health Association, the Institute for Animal Health at Pirbright, United Kingdom (invited), and the World Veterinary Congress in Cape Town, South Africa (invited). What do you plan to do during the next reporting period to accomplish the goals? In order to achieve our goals, we will be expanding our current studies to incorporate viral isolates obtained from sentinel animals to further understand the viral diversity of BTV isolates throughout the state of California. We propose to accomplish this objective using whole genome deep sequencing of contemporary and historic (>30 years) BTV viral isolates. This data will allow us to build upon our ongoing entomological field surveys to investigate the potential role of gene flow amongst field strains of BTV. This project will provide much-needed data linking the epidemiology and viral diversity of BTV by characterizing the sequences of all 10 segments, which is prerequisite to development of logical control strategies in endemic temperate regions. We also wish to expand our current studies to further understand the inter-seasonal BTV transmission cycle and potential overwintering strategy. We propose to accomplish this objective using both field and laboratory studies to identify if BTV overwinters in California through vertical transmission of virus within female C. sonorensis midges. Thus, this data will allow us to build upon our ongoing entomological field surveys to investigate the potential role of transovarial transmission of BTV in vector insects in virus overwintering. This project will provide much-needed data on the epidemiology of BTV by characterizing the inter-seasonal transmission cycle, which is prerequisite to development of logical control strategies in endemic temperate regions The data provided by these studies is essential to the future creation of accurate and predictive models of BTV infection of livestock, especially the objective data relating virus transmission in livestock to vector abundance, BTV infection prevalence and activity. Our studies confirm that anthropogenic factors, and not just meteorological ones, can be important in determining the prevalence of BTV infection of livestock on individual farms in California. Our overall goal is identify the relative importance of individual ecological drivers and specific management practices on vector populations and their relationship to the local and regional prevalence of BTV infection of livestock; however, this can only be fully completed by exploring viral diversity and interseasonal maintenance to gain a better perspective of global epidemiology, especially in application to predictive modeling systems. Incorporating pertinent and contemporary data into our models has been extremely important in making accurate predictions and establishing “what-if” scenarios for the likely effects of potential control measures to mitigate climate or anthropogenic change.
Impacts
What was accomplished under these goals?
Through successful completion and analysis of results of our surveillance program, we have identified meteorological and anthropogenic drivers of BTV infection among cattle housed at intensive dairy farms in California and we recently submitted a proposal to the NSF EEID program. The USDA NIFA AFRI grant has allowed us to continue our targeted surveillance strategy. The development of a one host/one vector ecological (SEIR) model, based on existing surveillance data to inform parameter estimates, has allowed us to direct our field studies to better characterize the ecological drivers of bluetongue virus (BTV) infection of livestock and for predictive modeling of future BTV outbreaks. Recent studies utilizing the combination of sentinel dairy cattle and entomological surveys over a 52-week period have identified several major paradigm shifts in the understanding of both the population dynamics of Culicoides midges and BTV infection within regional zones of California. The Sacramento (northern Central) Valley of California (CA) has a hot Mediterranean climate and a diverse ecological landscape that is impacted extensively by human activities, which include the intensive farming of crops and livestock. Waste-water ponds, marshes, and irrigated fields associated with these agricultural activities provide abundant larval habitats for C. sonorensis midges, in addition to those sites that exist in the natural environment. One study dairy farm had large operational waste-water lagoons, whereas the lagoon on another study farm was drained and remained dry during the study. Spring emergence and seasonal abundance of adult C. sonorensis on both farms coincided with rising vernal temperature. Paradoxically, the abundance of midges on the farm without a functioning waste-water lagoon was increased as compared to abundance on the farm with a waste-water lagoon system, indicating that this infrastructure may not serve as the sole, or even the primary larval habitat. Adult midges disappeared from both farms from late November until May; however, low numbers of parous female midges were detected in traps set during daylight in the inter-seasonal winter period. This latter finding is especially critical as it provides a potential mechanism for the “overwintering” of BTV in temperate regions such as northern CA and northern Europe. Precise understanding of temporal changes in the annual abundance and dispersal of Culicoides midges, in terms of intrinsic (e.g. density dependence) and extrinsic drivers (e.g. climate and hydrology) is essential for the creation of models to predict BTV infection of livestock and to evaluate sound abatement strategies. Additionally, there were differences in adult dispersion that could be due to either females questing patterns or larval production sites that are not accounted for. In a statewide survey in 1983, 55% of dairy lagoons sampled supported early developmental stages of C. sonorensis. This finding does not, however, preclude the importance of other developmental sites, even as small as hoof print impressions. Therefore, although dairy waste-water lagoons clearly provide a suitable development site for C. sonorensis, the broad range of habitats that can potentially be exploited by C. sonorensis on CA dairy farms would suggest that: 1. identification and evaluation of all potential larval habitats is necessary to characterize the ecology of C. sonorensis ; and 2. comprehensive larval control through lagoon habitat modification alone is unlikely to remove adults from agroecosystems such as the Sacramento Valley where irrigated crops and riparian corridors are abundant. In light of dramatic recent changes in the global distribution of BTV, a cross-sectional study was conducted to identify regional and local environmental, host, and anthropogenic risk factors associated with BTV seroprevalence among commercial dairy cattle in different ecological regions of California. A serosurvey of adult dairy cattle confirmed that BTV infection is prevalent throughout much of the state, although mean seroprevalence was significantly higher within two regions (Sacramento Valley and Southern California). A conditional autoregressive model was used to model BTV seroprevalence as a function of climatic, landscape, and host variables while accounting for spatial autocorrelation. High temperatures, high percentage cover of irrigated cropland and large herd sizes significantly increased BTV seroprevalence among dairy cattle herds. The analysis suggests that the combination of specific environmental, landscape, and animal host factors can create a favorable ecological niche for recurring annual seasonal transmission of BTV. Both studies highlight the need to further characterize ecological and environmental factors driving BTV infection and Culicoides vectors beyond the dairy infrastructure. We have made substantial progress with this project in collecting field data among dairy farms, necessary to construct predictive models. We have also constructed a reliable surveillance network that can be easily adapted for different livestock systems. Therefore, the final portion of this project is to adapt our current surveillance system to further understand the variability/similarity of endemic viral strains to enhance our current epidemiologic models. As a direct result, these models will be used for the logical development of practical and cost-effective methods to reduce numbers of Culicoides midges on individual farms or within flocks thereby reducing the risk of BTV transmission and other midge transmitted infections of livestock. The use of a comprehensive surveillance system on local dairy farms has allowed us to better assess and understand the natural seasonal transmission of BTV infection among diary cattle. Ultimately, in adapting this tool during the non-seasonal period of transmission will allow us to better predict actual risk of virus transmission to all livestock. Our long-term goal, therefore, is to develop accurate data pertaining to relative vector abundance, attack rates, and BTV prevalence from our field studies, and to utilize this data in developing an improved model for risk estimation.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
1. Maclachlan NJ, Henderson C, Schwartz-Cornil I, Zientara S (2013) The immune response of ruminant livestock to bluetongue virus: From type I interferon to antibody. Virus Res.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Maclachlan, N.J., Wilson, W.C., Crossley, B.M., Mayo, C.E., Jasperson, D.C., Breitmeyer, R.E., Whiteford, A.M., 2013. Novel serotype of bluetongue virus, western North America. Emerg Infect Dis 19, 665-666.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Maclachlan, N.J., Mayo, C.E., 2013. Potential strategies for control of bluetongue, a globally emerging, Culicoides-transmitted viral disease of ruminant livestock and wildlife. Antiviral Res 99, 79-90.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Mayo, C.E., Osborne, C.J., Mullens, B.A., Gerry, A.C., Barker, C.M., Gardner, I.A., Reisen, W.K., MacLachlan, N.J., 2013. Seasonal variation and impact of waste-water lagoons as larval habitat on the population dynamics of Culicoides sonorensis midges at two dairy farms in Northern California. PLOS ONE, DOI: 10.1371/journal.pone.0089633.
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2014
Citation:
Osborne, C.J., Mayo, C.E., Mullens B.A., MacLachlan, N.J., 2013. Estimating Culicoides sonorensis biting midge abundance using digital image analysis (in press).
|
Progress 01/01/12 to 12/31/12
Outputs
OUTPUTS: Throughout the last year we have made substantial progress in completing field studies to further characterize the ecological drivers of bluetongue virus (BTV) infection among Culicoides vectors and ruminant hosts for the predictive modeling of an emerging, economically important arboviral disease. Specific objectives were to establish/implement : 1. a spatial seroprevalence study to identify environmental and land use characteristics associated with regional (local scale) BTV infection rates of dairy cattle throughout California; 2. an entomological survey of C. sonorensis midges collected along transects centered on dairy waste-water lagoons on individual dairy farms (one of which then drained the major lagoon habitat) to characterize the population dynamics of C. sonorensis midges and their associated BTV infection rates; and 3. host selection feeding preferences of C. sonorensis biting midges by molecular characterization of bloodmeals of midges collected at different sites. The results have been presented at a number of meetings including: local dairy industry, California Department of Food and Agriculture (CDFA), the European Society of Vector Ecology (invited), the American Association of Veterinary Laboratory Diagnosticians, United States Animal Health Association, the Institute for Animal Health at Pirbright, United Kingdom (invited), and the World Veterinary Congress in Cape Town, South Africa (invited). These studies have also allowed us the ability to instruct and train undergraduate, DVM and graduate academic students in field and laboratory research. Most of this work has occurred on dairy farms using a sentinel cattle network, as prescribed by the OIE code. The dairies offered a remarkable ecological situation where animals, vectors, meteorological conditions, and anthropogenic factors can be readily measured and managed for a period of 3 years. Through successful completion and analysis of results of our surveillance program, we have identified key meteorological, anthropogenic and land use factors influencing BTV infection among cattle housed at intensive dairy farms in California and we recently leveraged this strategy into funding through the USDA NIFA AFRI program. In conjunction with the progress we have made under the NIFA grant, we will expand our surveillance to incorporate free-ranging livestock species (i.e. beef cattle operations, sheep flocks) to fully define the epidemiology of BTV infection in specific regions of California. We propose to accomplish this objective using beef cattle and sheep as the model of a free-ranging livestock species, which is logical given their availability and ease of handling. This project will provide much-needed data on the epidemiology of BTV infection among livestock in California, and the ecological niches required for vector, host, and BTV transmission. Acquisition of this data is pre-requisite to building accurate predictive models, especially in the face of climate change and all of its attendant potential impacts on emergence of arboviral diseases. PARTICIPANTS: This project is a collaborative effort involving individuals at the UC, Davis School of Veterinary Medicine, UC Davis Extension, University of California, Riverside, California Department of Food and Agriculture, California Animal Health Laboratory, local veterinarians, California Woolgrowers, and local dairy producers. We intend increasingly interacting with the California Cattlemens Association. These extensive interactions and collaborations are critical to the intensive surveillance studies that will underpin our ongoing efforts to model this economically important arboviral disease of livestock. The study also has provided a wonderful training environment for undergraduate, graduate and post-doctoral students. TARGET AUDIENCES: The target audience of the predictive modeling studies included in the project will be decision makers who focus on: 1. vector borne diseases of livestock and humans, 2. regulation of animal movement, 3. potential impacts of climate change, and 4. livestock production systems. The goal is to prepare the state and nation for emergence of any disease transmitted by biting Culicoides midges, specifically an exotic and/or virulent strain of bluetongue virus, epizootic hemorrhagic disease virus, African horse sickness virus, or any other related pathogen that might invade the United States. The predictive model that we develop should identify optimal control strategies that might be utilized in such an event. PROJECT MODIFICATIONS: There are no current modifications to the project described
Impacts
Findings from the entomological and sentinel animal studies completed in the project to date confirm the importance of using sensitive surveillance methods for both midge collection and virus detection in epidemiological studies of BTV infection. Additionally, there is no national surveillance of BTV infection in the U.S. and our own recent studies have focused exclusively on dairy farms. Potential drivers of vectorial capacity must be thoroughly characterized prior to emergence of virulent BTV in California; it is especially critical that the transmission parameters (attack rates, biting rates, infection rates) of all vector species be defined before such an event. Thus, we propose to build upon our ongoing epidemiologic investigations of sentinel dairy cattle to include free-ranging livestock and environments during the seasonal period of transmission (July-November, 2013). Specifically, we will evaluate sentinel beef cattle and sheep in selected herds/flocks to determine seasonal occurrence of BTV infection and vector Culicoides midge abundance. Acquisition of this data will allow us to determine the relationship of management practices and rates of infection and abundance of Culicoides midges to BTV seroconversion of range livestock. Additionally, we have partnered with collaborators in South Africa who are conducting similar studies characterizing the epidemiology African Horse Sickness, a closely related orbivirus. Results from the entirety of these field studies will be used to improve a deterministic ecological model we have constructed to quantify risk of BTV transmission among livestock. The model establishes a quantifiable framework to guide mitigation strategies.
Publications
- Mayo, C.E., Mullens, B.A., Gerry, A.C., Barker, C.M., Mertens, P.P., Maan, S., Maan, N.,Gardner, I.A., Guthrie, A.J., Maclachlan, N.J., 2012, The combination of abundance and infection rates of Culicoides sonorensis estimates risk of subsequent bluetongue virus infection of sentinel cattle on California dairy farms. Vet Parasitol 187, 295-301.
- Mayo, C.E., Gardner, I.A., Mullens, B.A., Barker, C.M., Gerry, A.C., Guthrie, A.J., MacLachlan, N.J., 2012, Anthropogenic and meteorological factors influence vector abundance and prevalence of bluetongue virus infection of dairy cattle in California. Vet Microbiol 155, 158-164.
- Maclachlan, N.J.: Emerging viral diseases; the example of bluetongue from Theiler to climate change. The Sir Arnold Theiler Memorial Lecture, Pretoria, South Africa, 2012
- Mayo, C.E., Mullens, B.A., Gardner, I.A., Gerry, A.C., Barker, C.M., MacLachlan,N.J., Epidemiology of BTV infection among California ruminants, American College of veterinary internal medicine, New Orleans, Louisiana, 2012
- Mayo, C.E., Mullens, B.A., Gardner, I.A., Gerry, A.C., Barker, C.M., MacLachlan,N.J., Anthropogenic and environmental drivers of BTV infection in California, United States Animal Health Association, Greensboro, North Carolina, 2012
- Mayo, C.E., Mullens, B.A., Gardner, I.A., Gerry, A.C., Barker, C.M., MacLachlan,N.J., Surveillane of Culicoides sonorensis and sentinel dairy cattle for bluetongue virus infection in California, Entomological Society of America, Knoxville, Tennessee, 2012
- Mayo, C.E., Mullens, B.A., Gardner, I.A., Gerry, A.C., Barker, C.M., MacLachlan,N.J., The combination of abundance and infection rates of Culicoides sonorensis estimates risk of subsequent bluetongue virus infection of sentinel cattle on California dairy farms, American Association of Veterinary Laboratory Diagnosticians, Greensboro, North Carolina, 2012
- Mayo, C.E., Mullens, B.A., Gardner, I.A., Gerry, A.C., Barker, C.M., MacLachlan,N.J., Characterization of the epidemiology of bluetongue virus infection among Culicoides midges and sentinel dairy cattle to quantify risk and guide mitigation strategies to reduce transmission, European society of vector ecology, Montpellier, France, 2012
- Maclachlan, N.J., Wilson, W.C., Crossley, B.M., Mayo, C.E., Jasperson, D.C., Breitmeyer, R.E. and Whiteford, A.M.(2013). Novel serotype of bluetongue virus, western North America. Emerg. Infect. Dis., in press
- Weyer, C.T., Quan, M., Joone, C., Lourens, C.W., Maclachlan, N.J. and Guthrie, A.J.(2013). African horse sickness in naturally infected, imunised horses. Eq. Vet. J., 45: 117-119 Crafford, J.E., Lourens, C.W., Gardner, I.A., Maclachlan, N.J. and Guthrie, A.J.(2013). Passive transfer and decay of maternal antibody against African horse sickness virus in South African Thoroughbred foals. Eq. Vet. J., in press Guthrie, A.J., Maclachlan, N.J., Joone, C., Ourens, C.W., Weyer, C.T., Quan, M., Monyai, M.S. and Gardner, I.A.(2013). Diagnostic accuracy of a duplex real-time reverse transcription quantitative PCR assay for detection of African horse sickness virus. J. Virol. Methods, 189: 30-35
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: Throughout the last year we have further characterized the seasonal abundance of Culicoides sonorensis and respective BTV infection rates on particular dairy farms within the Central Valley. The results have been presented at a number of meetings comprising: local dairy industry, the American Association of Veterinary Laboratory Diagnosticians, Pirbright, and World Veterinary Congress held in South Africa. The California Department of Food and Agriculture has been instrumental in helping facilitate the research; therefore, talks have been administered to these audiences in order to deliver results, facilitate communication, and instruct on methods of sampling for appropriate surveillance and diagnosis within the study. These studies have also allowed us the ability to instruct and train DVM and graduate students in field and laboratory research. Through successful completion and analysis of results of our surveillance program, we have identified key meteorological and anthropogenic drivers of BTV infection among cattle housed at intensive dairy farms in California and we recently leveraged this strategy into funding through the USDA NIFA AFRI program. This substantial grant will allow us to continue this surveillance and to develop predictive models for further characterizing the ecological drivers of bluetongue virus (BTV) infection of livestock and for predictive modeling of future BTV outbreaks. PARTICIPANTS: This project has been a collaborative effort involving the University of California, Davis (UC, Davis) Veterinary Teaching Hospital, UC, Davis extension, University of California, Riverside, California Department of Food and Agriculture, California Animal Health Laboratory, local veterinarians, California Woolgrowers, and local dairy producers. Through these interactions and collaborations, surveillance efforts have not only thrived but grown to encompass 3 solid years of data approaching a systems based approach to understanding vector borne disease. The people involved in these efforts allow us to gain the knowledge about the host, environment, and vector so that thoughtful teaching and model building strategies can be constructed. A combination of undergraduate students, graduate students, and local veterinarians have come together and sought out the opportunity to be trained on particular aspects this project. Some of these students are now advancing their careers in veterinary school and other laboratories. TARGET AUDIENCES: Upon completion of the predictive modeling, the target audience of this research will be decision makers that focus on both vector borne disease, animal movement, climate change, and dairy production systems. The goal is to minimize the cost of vector borne disease transmission via Culicoides vectors should an exotic and/or virulent strain of bluetongue virus, epizootic hemorrhagic disease, or African horse sickness invade the United States. Furthermore, the goal is to maximize the ability to implement effective control strategies at appropriate times should an epidemic occur such at that seen during 2006 when BTV8 invaded Europe. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Findings from the entomological studies confirm the importance of using sensitive surveillance methods for both midge collection and virus detection in epidemiological studies of BTV infection. Our results confirm those of prior studies showing regional variation in the prevalence of BTV infection of livestock throughout California, with defined areas of exposure. Sentinel cattle from coastal northwestern California were consistently negative whereas there was a non-uniform distribution of BTV infection amongst cattle on dairy farms in the Central Valley. The BTV-free status of the northwestern region is probably attributable to the cooler temperatures in this area and its effect on the vectorial capacity of resident insect vector populations. Vector abundance and BTV infection prevalence at individual farms within the Central Valley was mirrored by the prevalence of BTV infection of sentinel cattle at each of the 4 farms studied. While mean maximum and minimum temperatures were similar at all of the 4 dairy farms, the variation in vector abundance most likely is the result of lagoon waste-water and irrigation management practices at individual farms. Dairy wastewater lagoon ponds are present on many dairy farms throughout California and are a major larval habitat as larvae thrive within the muddy embankments of gently sloping and polluted lagoons.Lagoon wastewater provides a cost effective irrigation and nitrogen source for corn grown on dairy farms for silage. Planting of corn typically begins in late April and early May, and the waste lagoons are slowly drained for irrigation providing moist, muddy habitats at the margins for larval C. sonorensis populations. Thus, extensive irrigation of crops coupled with the use of lagoon waste-water at individual farms likely promotes the expansion of resident populations of C. sonorensis midges and subsequent seasonal transmission of BTV to livestock. BTV infection rates of C. sonorensis midges that were detected earlier in the season than sentinel cattle in addition to the plurality of serotypes on individual dairy farms might suggest that the midge vector constitutes a reservoir of genetically divergent BTVs that potentially sustain the virus in seasonally endemic areas.The data does suggest infection prevalence may be misrepresented when UV light traps alone, a method most often used in routine vector surveillance, to collect female C. sonorensis midges.In summary, our studies confirm that anthropogenic factors, and not just meteorological ones, can be important in determining the prevalence of BTV infection of livestock on individual farms in California. This data indicates acquisition of accurate and relevant data is prerequisite to the development of meaningful modeling approaches for risk prediction of BTV transmission among livestock, which is the long term goal of these studies.
Publications
- Mayo, C.E., Mullens, B.A., Gerry, A.C., Barker, C.M., Mertens, P.P., Maan, S., Maan, N., Gardner, I.A., Guthrie, A.J., Maclachlan, N.J., 2012, The combination of abundance and infection rates of Culicoides sonorensis estimates risk of subsequent bluetongue virus infection of sentinel cattle on California dairy farms. Vet Parasitol, in press
- Mayo, C.E., Gardner, I.A., Mullens, B.A., Barker, C.M., Gerry, A.C., Guthrie, A.J., Maclachlan, N.J., 2011, Anthropogenic and meteorological factors influence vector abundance and prevalence of bluetongue virus infection of dairy cattle in California. Vet Microbiol, in press.
- Maclachlan, N.J., 2011, Bluetongue: history, global epidemiology, and pathogenesis. Prev Vet Med 102, 107-111.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: Within the last year, three studies have been performed: a cross sectional BTV seroprevalence study among adult dairy cattle; a longitudinal cohort analysis of BTV infection of sentinel dairy calves; and an entomologic survey. These studies were designed to proactively address the potentially increased risk of incursion of novel BTV serotypes into the western US, and to re-evaluate the epidemiology of BTV infection in the region; the last similar study was done some 30 years ago using diagnostic methods that have long since been replaced by more convenient and robust assays. Specific objectives achieved were to establish the: 1. BTV seroprevalence among adult cattle; 2. seasonal viral RNA/seroprevalence of BTV infection among sentinel calves; 3. serotypes and virus strains that are currently present in the region; 4. incidence of congenital and/or perinatal BTV infection of cattle, and whether or not such infections contribute to the natural epidemiology of BTV infection; 5. risk factors that contribute to BTV infection of susceptible livestock; and 6.vector abundance (of biting Culicoides midges, C. sonorensis, in particular) and species using a combination of trapping methods including animal baited aspirations. Appropriate statistical analyses have been completed and results have been presented at a number of meetings comprising: local dairy industry, the American Association of Veterinary Laboratory Diagnosticians, South African Equine Veterinary Association, Institute for Animal Health, Pirbright, and Emerging Diseases and Surveillance meeting in Vienna, Austria. The California Department of Food and Agriculture has been instrumental in helping facilitate the research; therefore, talks have been administered to these audiences in order to deliver results, facilitate communication, and instruct on methods of sampling for appropriate surveillance and diagnosis within the study. PARTICIPANTS: This project has been a collaborative effort involving the University of California, Davis (UC, Davis) Veterinary Teaching Hospital, UC, Davis extension, University of California, Riverside, California Department of Food and Agriculture, California Animal Health Laboratory, local veterinarians, California Woolgrowers, and local dairy producers. Through these interactions and collaborations, surveillance efforts have not only thrived but grown to encompass 3 solid years of data approaching a systems based approach to understanding vector borne disease. The people involved in these efforts allow us to gain the knowledge about the host, environment, and vector so that thoughtful teaching and model building strategies can be constructed. A combination of undergraduate students, graduate students, and local veterinarians have come together and sought out the opportunity to be trained on particular aspects this project. Some of these students are now advancing their careers in veterinary school and other laboratories. TARGET AUDIENCES: Upon completion of the predictive modeling, the target audience of this research will be decision makers that focus on both vector borne disease, animal movement, climate change, and dairy production systems. The goal is to minimize the cost of vector borne disease transmission via Culicoides vectors should an exotic and/or virulent strain of bluetongue virus, epizootic hemorrhagic disease, or African horse sickness invade the United States. Furthermore, the goal is to maximize the ability to implement effective control strategies at appropriate times should an epidemic occur such at that seen during 2006 when BTV8 invaded Europe. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Three studies have been completed within the reporting period of this project: 1. a cross sectional bluetongue virus (BTV) seroprevalence study among adult dairy cattle; 2. a longitudinal cohort analysis of BTV infection of sentinel dairy calves; and 3. an entomologic survey. These studies have provided current data on vector, host, and transmission parameters that will be incorporated in predictive transmission models. These modeling systems will allow us to better predict the risk of BTV infection of cattle within the western US while allowing adjustment for different climatic scenarios that are currently of great concern in the arboviral community. The epidemiological investigation was conducted during 2009-2010 and utilized herds of sentinel cattle. BTV seroprevalence among adult cattle (2-7 years of age) ranged from 0 to 90% with lowest seroprevalence in northwestern California, a region historically free of BTV infection. There was a non-uniform distribution of seroprevalence among older cattle throughout the remainder of the state. BTV viral RNA prevalence among sentinel dairy calves was highest during the seasonal transmission period (July - December). Although the sentinel calves were all enrolled during the interseasonal "over-wintering period" of BTV infection, a low prevalence of BTV infection was detected unexpectedly amongst 6 calves in the study cohort, and their dams were all seronegative. Sequence analysis confirmed homology of amplicons obtained from one calf's blood and colostrum. Together these data confirm both localized, vector-mediated, seasonal transmission of BTV as well as dissemination of BTV and/or viral nucleic acid to newborn calves following ingestion of colostrum. The second portion of the epidemiological investigation was to identify predictive drivers of BTV infection among cattle. The analysis confirmed transmission is strongly associated with both environmental (temperature, precipitation) and management practices, especially the use of dairy waste water for irrigation. These environmental and anthropogenic parameters increase vector abundance and promote increased risk of BTV transmission at specific farms (manuscript in final preparation). Recent studies have focused on determining vector abundance and predominant Culicoides vector species on local dairies with a combination of trapping methods. Preliminary analysis of the data indicates that there are marked differences in Culicoides abundance as determined by different trapping methods. Abundance levels peak during August as determined by both light and carbon dioxide trapping methods, whereas numbers of insects collected by animal baited aspiration do not peak until September. This suggests that measuring abundance with only conventional trapping methods, estimates typically used in current BTV models, might be misleading and inappropriate for determining true attack rates (biting rates) or vector to host ratios. This data will be used to estimate correlation to BTV seroconversion rates among cattle. Our goal, therefore, is to utilize data from our field studies in developing an improved model for risk estimation of Orbiviruses.
Publications
- Makoschey, B., Maclachlan, J., van Wuijckhuise, L., Kirschvink, N., dal Pozzo, F., Petit, H., Kaandorp-Huber, C., van Rijn, P., Sellal, E., Boinas, F., Cavirani, S., de Clerck, K., Lucientes, J., Meijies, C.P., Zientara, S., Meyer, G. and Thiry, E.: Bluetongue control in Europe new challenges and achievements. Berl. Munch. Tieraztl. Wochenschr., 122: 31-324, 2009.
- Mayo CE, Crossley BM, Hietala SK, Gardner IA, Breitmeyer RE, MacLachlan NJ, Colostral Transmission of Bluetongue Virus Nucleic Acid Among Newborn Dairy Calves in California, Transboundary and Emerging Dieseases. 2010, 57 (4), 277-281.
- Drew CP, Heller MC, Mayo C, Watson JL, MacLachlan NJ, Bluetongue virus infection activates bovine monocyte-derived macrophages and pulmonary artery endothelial cells, Vet Immunol Immunopathol. 2010, 136 (3-4), 292-296.
- Drew CP, Gardner IA, Mayo CE, Matsuo E, Roy P, MacLachlan NJ, Bluetongue virus infection alters the impedance of monolayers of bovine endothelial cells as a result of cell death, Vet Immunol Immunopathol. 2010 Jul; 136 (1-2): 108-115.
- Maclachlan, N.J.: Global implications of the recent emergence of bluetongue in Europe. Vet. Clin. Nth. Am., 26: 163-171, 2010 (invited)
- Guthrie, A.J.: Re-emergence of bluetongue, African horse sickness and other orbivirus diseases. Vet. Res., 41:35, 2010 (invited)
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: The recent incursion of ten novel serotypes of BTV into the US as well as similar events in Europe and elsewhere in the world motivated us to initiate a study to define the epidemiology of BTV infection in different regions of California. This longitudinal cohort study began in December, 2008, and was designed to proactively address the potentially increased risk of incursion of novel BTV serotypes or strains into the western US. Specific objectives were to establish the: 1. seasonal incidence of BTV infection among California cattle, 2. serotypes and virus strains that are currently present in the region, 3. incidence of congenital and/or perinatal BTV infection of cattle, and whether or not such infections contribute to the natural epidemiology of BTV infection (as they increasingly are proposed to do in Europe), and 4. potential environmental risk factors that contribute to BTV infection of susceptible livestock, and to predict how these might be modulated by climate change. This initial study provides the preliminary data and many of the reagents on which the future studies are based. The study utilizes herds of sentinel cattle, as recommended in the most recent OIE Code. A total of 123 calves from 10 dairy herds were enrolled between December, 2008 and March, 2009 to ensure the selection of calves that were born during the BTV-free period. BTV infection of ruminants in California is highly seasonal, occurring largely between late July and November. Monthly collection of serum and whole blood has continued from the sentinel cattle on dairies within four geographically distinct regions of the state, including the Pacific northwest region that historically has long been free of BTV infection (thus providing a negative cohort). These samples have been analyzed respectively by BTV-specific cELISA (serology) and BTV-group specific qRT-PCR (virus detection) assays. All samples that are positive by qRT-PCR are confirmed utilizing virus isolation and serotyped utilizing virus neutralization assays. The sequences of the L2 and S10 genes of putative viral strains will be compared with other field and laboratory sequences, including vaccine and prototype (ATCC) strains, obtained from the GenBank library and used to form phylogenetic trees. We already have made enormous progress with this project, which is now approximately 70% completed. The study will continue through March 2010 to ensure that we sample all sentinel calves for 12 months. This study will determine the serotypes and strains of BTV already enzootic in the state, and will quickly show whether or not changing climatic patterns have resulted in the incursion of previously exotic BTV serotypes. Seasonality and risk factors associated with the incidence of infection cannot be fully assessed until the end of the study, March 2010. Results have been presented to audiences within the UC Davis community, annual meetings of AAVLD/USAHA, and the BTV intensive committee at the USAHA annual meeting. Further distribution of results has occurred within the local community among participating producers and at their respective meetings. PARTICIPANTS: Dr. Maclachlan has been a member (chair of 2) of all OIE committees on BT since 1995. He recently developed and patented (in collaboration with Merial Inc.) recombinant canarypox virus vaccines to both BTV and related African horse sickness virus; he has numerous publications describing the global epidemiology of BTV and the pathogenesis of BT. Dr. Gardner has been extensively involved in epidemiologic studies involving livestock health, safety, and production. Drs. Hietala and Crossley head the diagnostic programs for BT in California (CAHFS), and run the cELISA and qRT-PCR assays that are central to the study. Dr. Mayo co-ordinates the project as the basis of her Ph.D. thesis research project. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Although the sentinel calves were all born in the interseasonal "over-wintering period" of BTV infection, a low cumulative incidence of BTV infection (as determined by viral RNA detection in blood) was detected unexpectedly amongst the study cohort. The lack of infection of the remaining calves (which constitute the vast majority of the sentinels) from December 2008 through August of 2009 reflects lack of exposure to the bites of BTV-infected Culicoides during these months, whereas the high incidence of the sentinel calves (54%) for BTV-specific antibodies reflects the ingestion of colostrum from seropositive dams (passive immunity). BTV was identified transiently by qRT-PCR (Ct values < 35) in 6 of the 123 calves, but confirmed by virus isolation from the blood of only a single calf located in Stanislaus County; this calf was qRT-PCR positive for viral nucleic acid from birth until three months of age (Ct 23, 25, 29) . BTV isolated from blood collected at the initial sampling was identified as BTV serotype 11 via virus neutralization assays with type-specific antisera. The epidemiological significance of this detection of BTV (or BTV viral RNA) in newborn calves is unknown but clearly warrants further investigation. Preliminary phylogenetic analyses of the virus isolated from the congenitally/perinatally infected calf confirm that the NS3 gene of this virus is very similar to that of another virus isolated from a local sheep that died of fulminate BT in 2008 (97% identity), but distinct from those of other strains and serotypes of BTV that previously have been isolated in California, including those of live attenuated vaccine viruses. Importantly, these preliminary results clearly confirm that local field strains of BTV can cause congenital or perinatal infection in cattle resulting in the presence of viremic newborn calves. The mechanism of this phenomenon, whether true congenital (in utero) infection or horizontal infection perhaps orally through infective colostrum remains entirely unknown, but similar phenomena have been described in Europe. With the exception of the one calf that was infected either congenitally or perinatally, active BTV infection was not detected in the sentinel calves until August of 2009. Since August, BTV infection has been identified in calves at four locations, but at low frequency (viral RNA prevalence of 10.5% and seroprevalence of 8.3% of the study population). These data confirm that BTV infection is highly seasonal in California, and that virus essentially disappears for much of the year, reappearing in the late summer/early Fall. The ramifications of any outbreak of virulent BT in the United States could be as devastating as those associated with the ongoing pandemic in Europe. It is important, prior to any crisis, that the epidemiology of BTV infection in California be thoroughly characterized, including a definitive characterization of the virus strains and serotypes that are currently present. Our goal, therefore, is to continue with current progress to determine what serotypes and genotypes of BTV are currently enzootic in California and explore potential role of congenital and/or perinatal infection.
Publications
- Maclachlan, N.J. 2009. Global implications of the recent emergence of bluetongue in Europe. Vet Clinics of North America, in press 2009.
- Jafari-Shoorijeh, S., Tamadon, A., Behzadi, M.A., Ramin, A.G., Samani, D., Rezajou, N., Amin-pou, A., Maclachlan, N.J., Osburn, B.I., Mahdavi, M. and Araskhani, A. 2009. High seroprevalence of bluetongue virus infection in sheep flocks in West Azerbaijan, Iran. Comp. Immunol. Microbiol. Infect. Dis., (in press).
- Worwa, G., Hilbe M., Ehrensperger, F., Chaignat, V., Hofmann, M.A., Griot C., Maclachlan, N.J. and Thuer, B.2009. Experimental transplacental bluetongue virus serotype 8 infection in sheep. Vet. Rec., 164: 499-500, 2009.
- Maclachlan NJ, Drew CP, Darpel KE, Worwa G.(2009) The pathology and pathogenesis of bluetongue, J Comp Pathol. 2009 Jul;141(1):1-16
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: We have continued characterization of the recombinant canarypox virus vectored bluetongue vaccine that was described in last year's report. This vaccine induces sterilizing immunity in vaccinated sheep. We also have continued studies into the pathogenesis of bluetongue disease, and the mechanism of increased vascular permeability in particular. These have included both in vitro and in vivo studies focused on distinguishing the relative contributions to vascular leakage of direct virus mediated endothelial injury versus the impact of host-derived proinflammatory mediators. PARTICIPANTS: Partner organizations: Merial Inc., (Drs. Robert Nordgren, Jules Minke and Jean-Christophe Audonnet); Department of Veterinary Tropical Diseases, University of Pretoria, South Africa (Drs. Alan Guthrie, Estelle Venter and Jannie Crafford), and Institute for Virology and Immunoprophylaxis, Switzerland (Drs. Griot and Worwa). TARGET AUDIENCES: Information from our studies is disseminated to national industry groups through the United States Animal Health Association as well as local industry group meetings. International dissemination occurs through the World Animal Health Organization (OIE), and the European Union (EFSA). PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The non-replicating vaccine we have developed offers an effective strategy for controlling bluetongue epizootics, which would be potentially very useful should North America ever experience any emergence of bluetongue similar to that now occurring throughout Europe. Characterization of the pathogenesis of bluetongue obviously is prerequisite to logical development of effective therapeutic interventional strategies.
Publications
- Schwartz-Cornil, I., Mertens, P.P., Contreras, V., Hemati, B., Pascale, F., Breard, E., Mellor, P.S., Maclachlan, N.J. and Zientara, S. (2008): Bluetongue virus: virology, pathogenesis and immunity. Vet. Res., 39: 46-56.
- Worwa, G., Thur, B., Griot, C., Hofmann, M., Maclachlan, N.J. and Chaignat, V.(2008): Clinical signs observed in Swiss sheep after experimental bluetongue virus serotype 8 infection. Schweiz Arch. Tierheilkd, 150: 491-498.
- Worwa, G., Hilbe M., Ehrensperger, F., Chaignat, V., Hofmann, M.A., Griot C., Maclachlan, N.J. and Thuer, B. (2008): Experimental transplacental bluetongue virus serotype 8 infection in sheep. Vet. Rec., in press
- Maclachlan, N.J., Crafford, J.E., Vernau, W., Gardner, I.A., Goddard, A., Guthrie, A.J. and Venter, E.H. (2008): Experimental reproduction of severe bluetongue in sheep. Vet. Pathol., 45: 310-315.
- Maclachlan, N.J. and Osburn, B.I.(2008): Induced brain lesions in calves infected with bluetongue virus. Vet. Rec., 162: 490-491.
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Progress 01/01/07 to 12/31/07
Outputs
OUTPUTS: The genes encoding the outer capsid proteins of a field strain of BTV serotype 17 were cloned into a recombinant canarypox vector. Sheep immunized with this recombinant expression system were protected against homologous virus challenge.
PARTICIPANTS: Parter organization - Merial Inc. Dr Robert Nordgren, Jules Minke and Jean Christophe Audonnet
Impacts
This non-replicating BTV vaccine offers an attractive strategy for controlling bluetongue epidemics, a strategy that assumes even greater significance given the recent emergence of seven new serotypes of BTV in North America and the ongoing disease pandemic in Europe.
Publications
- Boone, J.D., Balasuriya, U.B., Karaca, K., Audonnet, J-C., Yao, J., He L., Nordgren, R., Monaco F., Savini, G., Gardner, I.A. and MacLachlan, N.J.: Recombinant canarypox virus vaccine co-expressing genes encoding the VP2 and VP5 outer capsid proteins of bluetongue virus induces high level protection in sheep. Vaccine, 25: 672-678, 2007
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Progress 01/01/06 to 12/31/06
Outputs
The genes encoding the outer capsid proteins VP2 and VP5 of a field strain of bluetongue virus (BTV) serotype 17 (BTV-17) from California were cloned into a recombinant canarypox virus expression vector. Sheep immunized with this recombinant vaccine developed neutralizing antibodies to BTV-17, and were completely resistant to challenge infection with the homologous virus strain.
Impacts
This no-replicating recombinant bluetongue virus vaccine offers a safe and effective strategy for preventing losses associated with BTV infection, and for controlling future incursions of exotic strains of the virus. While this vaccine strategy potentially is very important for animal production in the United States, it has the potential for true global impact.
Publications
- Boone, J.D., Balasuriya, U.B., Karaca, K., Audonnet, J-C., Yao, J., He L., Nordgren, R., Monaco F., Savini, G., Gardner, I.A. and MacLachlan, N.J.: Recombinant canarypox virus vaccine co-expressing genes encoding the VP2 and VP5 outer capsid proteins of bluetongue virus induces high level protection in sheep. 2006. Vaccine, in press
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Progress 01/01/05 to 12/31/05
Outputs
The genes encoding the outer capsid proteins VP2 and VP5 of all 5 endemic serotypes of blueotngeu virus (BTV) have been cloned and sequenced. Those of BTV serotype 17 now have been cloned into a non-replicating expression vector and used to immunize sheep. The immunized sheep developed neutralizing antibodies to BTV serotype 17.
Impacts
This non-replicating vaccine offers an extremely safe strategy for preventing losses associated with bluetongue virus infection of ruminants in the United States, and the strategy we have developed provides a vital solution to potential incursion of exotic serotypes of bluetongue virus.
Publications
- No publications reported, 2005
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Progress 01/01/04 to 12/31/04
Outputs
The genes encoding the outer capsid proteins VP2 and VP5 of all 5 endemic US serotypes of bluetongue virus have been cloned and sequenced. We now are evaluating their expression in several different vectors.
Impacts
Non-replicating vaccines are needed to reduce losses associated with bluetongue disease of ruminants in the US and, potentially, to control incursions of currently exotic strains of bluetongue virus.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
The genes encoding the outer capsid proteins VP2 and VP5 of all 5 US serotypes of bluetongue virus successfully have been cloned. Sequencing of most of these clones has been completed. The necessary shuttle vectors also have been acquired.
Impacts
Non-replicating vaccines are needed to reduce losses associated with bluetongue disease of ruminants in the US and, potentially, to control incursions of currently exotic strains of bluetongue virus.
Publications
- MacLachlan NJ. 2004. Bluetongue: Pathogenesis and duration of viremia. Veterinaria Italiana, in press
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Progress 01/01/02 to 12/31/02
Outputs
The goal of this project is to define the pathogenesis of bluetongue virus (BTV) infection of cattle, and to characterize the evolution of BTV. In collaboration with Dr. Brad Mullens at UC Riverside we have investigated the interaction of BTV with its insect vector (Culicoides sonorensis) in the Chino Basin area. Molecular genetic analyses of individual BTV gene segments indicate that different virus strains co-circulate on specific farms, thus we compared these strains to those associated with outbreaks of bluetongue disease in ruminants elsewhere in California.
Impacts
Bluetongue remains the only OIE List A disease that is endemic in the US. Accurate determination of the epidemiology of BTV infection in endemic areas such as California is prerequisite to rationalization of current international non-tariff trade barriers pertaining to bluetongue, and to development of improved diagnostic and vaccine technologies for BTV.
Publications
- Bonneau KR, Topol JB, Gerry AC, Mullens BA, Velten RK, MacLahclan NJ. Variation in the NS3/3A gene of blueotngue viruses contained in Culicoides sonorensis collected from a single site in southern California. Virus Research 84: 59-65, 2002
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Progress 01/01/01 to 12/31/01
Outputs
The goal of this project is to define the pathogenesis of bluetongue virus (BTV) infection of cattle, and to characterize the evolution of BTV. In collaboration with Dr. Brad Mullens at UC Riverside we have investigated the interaction of BTV with its insect vector (Culicoides sonorensis) in the Chino Basin area. Molecular genetic analyses of individual BTV gene segments indicate that different virus strains co-circulate on specific farms, thus we compared these strains to those associated with outbreaks of bluetongue disease in ruminants elsewhere in California.
Impacts
Bluetongue remains the only OIE List A disease that is endemic in the US. Accurate determination of the epidemiology of BTV infection in endemic areas such as California is prerequisite to rationalization of current international non-tariff trade barriers pertaining to bluetongue, and to development of improved diagnostic and vaccine technologies for BTV.
Publications
- Gerry AC, Mullens BA, MacLachlan NJ, Mecham JO. Seasonal transmission of bluetongue virus by Culicoides sonorensis (Diptera: Ceratopogonidae) at a Southern California dairy and evaluation of vector capacity as a predictor of bluetongue virus transmission. Journal of Medical Entomology, 38: 197-209, 2001
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Progress 01/01/00 to 12/31/00
Outputs
The goal of this project is to define the pathogenesis of bluetongue virus (BTV) infection of cattle, and to characterize the evolution of BTV. In collaboration with Dr. Brad Mullens at UC Riverside we have investigated the interaction of BTV with its insect vector (Culicoides sonorensis) in the Chino Basin area. Molecular genetic analyses of individual BTV gene segments indicate that different virus strains co-circulate on specific farms, and we now are comparing these strains to those associated with outbreaks of bluetongue disease in ruminants elsewhere in California. We also have shown that the strains of BTV that circulate in California are distinct from those in Asia.
Impacts
Bluetongue remains the only OIE List A disease that is endemic in the US. Accurate determination of the epidemiology of BTV infection in endemic areas such as California is prerequisite to rationalization of current international non-tariff trade barriers pertaining to bluetongue, and to development of improved diagnostic and vaccine technologies for BTV.
Publications
- Gerry AC, Mullens BA, MacLachlan NJ, Mecham JO. Seasonal transmission of bluetongue virus by Culicoides sonorensis (Diptera: Ceratopogonidae) at a Southern California dairy and evaluation of vector capacity as a predictor of bluetongue virus transmission. J Med Entomol, in press, 2001
- Bonneau KR, Zhang NZ, Wilson WC, Zhu JB, Zhang FQ, Li ZH, Zhang KL, Xiau L, Xiang WB, MacLachlan NJ. Phylogenetic analysis of the S7 gene does not segregate Chinese strains of bluetongue virus into a single topotype. Archiv Virol 145: 1163-1171, 2000
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Progress 01/01/99 to 12/31/99
Outputs
The goal of this study is to define the pathogenesis of bluetongue virus (BTV) infection of cattle, and to characterize the genetic evolution of BTV. Molecular genetic analyses of field strains of BTV from the western United States indicate that the virus is subject to natural gene reassortment and drift, and that distinct populations of virus co-circulate. This finding has considerable relevance to BTV-induced disease, to attempts to develop efficacious vaccines, and to trade negotiations.
Impacts
Our data indicates that evolution of BTV in the western US differs from that in other areas of the world, specifically southern China, thus strains of BTV appear to evolve in their own unique ecosystems. This finding has considerable relevance to efforts to rationalize the international trade of ruminants and germplasm, and the current deleterious impact of BTV infection thereon.
Publications
- 1. ZHANG N, MACLACHLAN NJ, BONNEAU K, ZHU J, LI Z, ZHANG K, ZHANG F, XIA L, WENBING X. 1999. Identification of seven serotypes of bluetongue virus from China. Vet. Rec.,145: 427-429.
- 2. BONNEAU KR, ZHANG N, ZHU J, ZHANG F, LI Z, ZHANG K, XIAO L, XIANG W, MACLACHLAN NJ. 1999. Sequence comparison of the L2 and S10 gene segments of bluetongue viruses from the United States and the People's Republic of China. Virus. Res., 61: 153-160.
- 3. BONNEAU KR, ZHANG NZ, WILSON WC, ZHU JB, ZHANG FQ, LI ZH, ZHANG KL, XIAU L, XIANG WB, MACLACHLAN NJ. 1999. Phylogenetic analysis of the S7 gene does not segregate Chinese strains of bluetongue virus into a single topotype. Archiv. Virol., in press.
- 4. GERRY AC, MULLENS BA, MACLACHLAN NJ, MECHAM JO. 1999. Seasonal transmission of bluetongue virus by Culicoides sonorensis (Diptera: Ceratopogonidae) at a Southern California dairy and evaluation of vector capacity as a predictor of bluetongue virus transmission. J. Med. Entomol., submitted.
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Progress 01/01/98 to 12/31/98
Outputs
The goal of this study is to define the pathogenesis of bluetongue virus (BTV) infection of cattle, and to characterize the genetic evolution of BTV. Molecular genetic analyses of field strains of BTV from the western United States indicates that the virus is subject to natural gene reassortment and drift, and that distinct populations of virus co-circulate. This finding has considerable relevance to BTV-induced disease, to attempts to develop efficacious vaccines, and to trade negotiations. Our data indicates that evolution of BTV in the western US differs from that in other areas of the world, specifically southern China, thus strains of BTV appear to evolve in their own unique ecosystems. This finding has considerable relevance to efforts to rationalize the international trade of ruminants and germplasm, and the current deleterious impact of BTV infection thereon.
Impacts
(N/A)
Publications
- 1. PIERCE CM, BALASURIYA UBR, MACLACHLAN NJ. Phylogenetic analysis of the S10 gene of field and laboratory strains of bluetongue virus from the United States. Virus Res, 55: 15- 27, 1998
- 2. ZHANG N, MACLACHLAN NJ, BONNEAU K, ZHU J, LI Z, ZHANG K, ZHANG F, XIA L, WENBING X: Identification of seven serotypes of bluetongue virus from China. Vet. Rec., in press
- 3. BONNEAU KR, ZHANG N, ZHU J, ZHANG F, LI Z, ZHANG K, XIAO L, XIANG W, MACLACHLAN NJ: Sequence comparison of the L2 and S10 gene segments of bluetongue viruses from the United States and the People's Republic of China. Virus. Res., submitted for publication
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Progress 01/01/97 to 12/01/97
Outputs
The goal of this study is to define the pathogenesis of bluetongue virus (BTV) infection of cattle, and to characterize the genetic evolution of BTV. Molecular genetic analyses of field strains of BTV from the western United States indicates that the virus is subject to natural gene reassortment and drift, and that distinct populations of virus co-circulate. This finding has considerable relevance to BTV-induced disease, and to attempts to develop efficacious vaccines, and to trade neogitiations. In paraticular, our data indicates that evolution of BTV in the western US differres from that in other areas of the world, thus strains of BTV appear to evolve in their own unique ecosystems.
Impacts
(N/A)
Publications
- 1. PIERCE CM, BALASURIYA UBR, MACLACHLAN NJ. Phylogenetic analysis of the S10 gene of field and laboratory strains of bluetongue virus from the United States. Virus Res, in press
- 2. MACLACHLAN NJ, PIERCE CM, de MATTOS CA, de MATTOS CC, OSBURN BI. Evolution of bluetongue virus in the western United States. Proc US Animal Hlth Assoc, in press
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Progress 01/01/96 to 12/30/96
Outputs
The goal of this study is to define the pathogenesis of bluetongue virus (BTV) infection of cattle, and to characterize the genetic evolution of BTV. Molecular genetic analyses of field strains of BTV from the western United States indicates that the virus is subject to natural gene reassortment and drift, and that distinct populations of virus co-circulate. This finding has considerable relevance to BTV-induced disease, and to attempts to develop efficacious vaccines.
Impacts
(N/A)
Publications
- DE MATTOS CC, de MATTOS CA, MACLACHLAN NJ, GIAVEDONI L, YILMA T, OSBURN BI. Phylogenetic comparison of the S3 gene of United States prototype strains of bluetongue virus and field isolates from California. J. Virol., 70: 5735-5739, 1996.
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Progress 01/01/95 to 12/30/95
Outputs
The goal of this study is to define the pathogenesis of bluetongue virus (BTV) infection of cattle, and to characterize the genotypic and phenotypic determinants of neutralization of BTV. We have infected calves with BTV and then determined the interval thereafter when virus could be transmitted to susceptible sheep by the bites of vector insects. This interval subsequently was compared to the interval after infection when virus could be detected by virus isolation and PCR analysis. The data indicate that insect feeding was the least sensitive method of detecting BTV in cattle blood. We also characterized the neutralizing determinants of BTV serotype 17 by sequencing of the L2 gene from variants of the virus that are resistant to neutralization by neutralizing monoclonal antibodies. Finally, we have initiated molecular genetic analyses to determine the evaluation of BTV in the western United States.
Impacts
(N/A)
Publications
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Progress 01/01/94 to 12/30/94
Outputs
The initial goal is to define the pathogenesis of bluetongue virus (BT//) infection of cattle. We have shown that prolonged viremia in BTV-infected cattle is not a consequence of either antigenic drift of the virus, or from deficits in the host's antiviral response. We have shown that virus associates with blood cells, especially erythrocytes, is responsible for prolonged viremia. In vitro studies have illustrated the mechanism which likely is responsible for this novel interaction between BTV and bovine blood cells. Our second objective is to characterize the phenotypic and genotypic variation of BTV in California. We have shown that BTV strains circulating in CA are extremely heterogenetic. This variation arises by both reassortment of individual viral gene segments and genetic drift. Our studies further suggest that evolution of the virus is complex, with individual strains evolving via different evolutionary pathways. In total, the results suggest that BTV behaves
as a quasispecies in nature.
Impacts
(N/A)
Publications
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Progress 01/01/93 to 12/30/93
Outputs
Our first objective was to define the pathogenesis of bluetongue virus (BTV) infection of cattle. We have shown that prolonged viremia in BTV-infected cattle is not a consequence of either antigenic drift of the virus during infection, or from deficits in the host's antiviral response. We have shown that virus associates with blood cells and association with erythrocytes in particular is responsible for prolonged viremia. In vitro studies have illustrated the mechanism which likely is responsible for this novel interaction between BTV and bovine blood cells. Our second objective was to characterize the phenotypic and genotypic variation of BTV in California. We have shown that BTV strains circulating in CA are extremely heterogenetic. This variation arises by both reassortment of individual viral gene segments as well as genetic drift. Our studies further suggest that evolution of the virus is complex, with individual strains evolving via different evolutionary
pathways. In total, the results suggest that BTV behaves as a quasispecies in nature.
Impacts
(N/A)
Publications
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Progress 01/01/92 to 12/30/92
Outputs
In these studies we have identified the bovine blood mononuclear cells which support replication of BTV in-vitro by double-label fluorescence - activated cell sorter analysis. We have shown that BTV replicates in bovine CD4 positive T cells and monocytes, but not significantly in B cells and gamma/delta or CD8 positive T cells. We also have characterized the ultrastructural interaction of BTV with bovine blood cells, including erythrocytes and mononuclear cells. Our findings have allowed us to develop a cogent theory as to the mechanism of the prolonged viremia which occurs in BTV-infected cattle. Infection of calves indicates that local lymph nodes are the initial site of replication of BTV, and that subsequent association of BTV with blood cells is non-selective. Thus BTV associates with platelets, erythrocytes, neutrophils and mononuclear cells but, late in the course of viremia, it most consistently is associated with erythrocytes. We also have undertaken epitope
mapping studies of the neutralization sites of field and prototype strains of BTV. Our results indicate that epitopes recognized by individual neutralizing monoclonal antibodies (MAbs) can serve as major or minor determinants of neutralization amongst field strains of some serotypes of BTV. Further, that BTV serotypes 10 and 17 share a common neutralizing epitope.
Impacts
(N/A)
Publications
- BREWER, A.W. and MACLACHLAN, N.J. 1992. Ultrastructural characterization of the association of bluetongue virus with bovine erythrocytes in-vitro. Vet Pathol 29: 356-359.
- MACLACHLAN, N.J., ROSSITTO, P.V., HEIDNER, H.W., IEZZI, L.G., YILMA, T., DEMAULA, C.D. and OSBURN, B.I. 1992. Variation amongst the neutralizing epitopes of bluetongue viruses isolated in the United States. Vet Microbiol 31: 303-316.
- ROSSITTO, P.V., and MACLACHLAN, N.J. 1992. Neutralizing epitopes of bluetongue viruses present in the United States. J Gen Virol 73: 1947-1952.
- BARRATT-BOYES, S.M., ROSSITTO, P.V., STOTT, J.L., and MACLACHLAN, N.J. 1992. Flow cytometric analysis of in-vitro bluetongue virus infection of bovine blood mononuclear cells. J Gen Virol 73: 1953-1960.
- NUNAMAKER, R.A., ELLIS, J.A., WIGINGTON, J.G. and MACLACHLAN, N.J. 1992. The detection of intracellular bluetongue virus particles within ovine erythrocytes. Comp Biochem Physiol 101A:471-476.
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Progress 01/01/91 to 12/30/91
Outputs
The broad objective of this project is to better characterize the epizootiology of bluetongue virus (BTV) infection as it occurs in California, by defining the pathogenesis of BTV infection of cattle and the molecular biology of the virus itself. Accomplishments to date includes: 1. We are further characterizing the pathogenesis of BTV infection of cattle. In-vitro studies indicate that BTV-replicates in bovine monocytes and CD4+T cells. We now wish to determine whether similar cells are infected in-vivo, and have undertaken pathogenesis studies in calves with lymphatic cannulation to address this aspect. 2. We are attempting to define the evolution of BTV as it is occurring in California, with the objective of improving vaccines and diagnostic methodologies. We have phenotypically and genetically compared a variety of field isolates of BTV obtained in the state. These studies are continuing at considerable rate.
Impacts
(N/A)
Publications
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Progress 01/01/90 to 12/30/90
Outputs
The broad objective of this project is to better characterize the epizootiology of bluetongue virus (BTV) infection as it occurs in California, by defining the pathogenesis of BTV infection of cattle and the molecular biology of the virus itself. Acomplishments to date includes: Refinement of techniques for immunofluorescent and immunohistochemical localization of BTV antigens in tissues. Specifically, we have used a panel of BTV-specific monoclonal antibodies (MAbs) to localize a variety of BTV structural and non-structural proteins in infected cells. Identification of tissues in which BTV replicates after experimental infection of calves. Eleven colostrum-deprived, isolation reared calves were intravenously inoculated with BTV, and 2 similar calves received a placebo. Viral tropism then was determined by viral isolation on a variety of tissues, and immunohistochemical staining of these tissues for the presence of viral antigens. The virus rapidly replicates to high
titers in lymphoid tissues such as lymph nodes, spleen and thymus, whereas the bone marrow is largely spared. This suggests that the highly cell-associated viremia which characteristically occurs in BTV-infected cattle does not reflect infection of hemopoietic stem cells in bone marrow.
Impacts
(N/A)
Publications
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Progress 01/01/89 to 12/30/89
Outputs
The broad objectives of this grant are to better characterize the epizootiology of BTV infection as it occurs in California. Specific accomplishments include: 1) Identification of tissues in which BTV replicates after experimental infection of calves; specifically, the virus apparently replicates in lymphoid tissues such as lymph nodes, speen and thymus, whereas the bone marrow is largely spared. This suggests infection of blood cells does not reflect infection of hemopoietic stem cells in bone marrow. 2) Developed directly FITC-conjugated BTV-specific monoclonal antibodies and used these for immunofluorescent staining of BTV-infected of purified bovine blood mononuclear cells. Using this technique, as well as double immunohistochemical labelling, we will characterize the pathogenesis of infection of bovine blood cells during natural BTV infection of cattle. 3) This grant has supported part of the salary of Mr. L. Iezzi, who has used the technique of 2-dimensional
oligonucleotide fingerprinting to compare individual BTV genome segments. The viruses with which he works were isolated in the western United States. This technique facilitates genetic comparison of field viruses and has vividly demonstrated the extreme heterogeneity of BTV; such observations will have extremely important ramifications for future vaccine development.
Impacts
(N/A)
Publications
- NO PUBLICATIONS REPORTED THIS PERIOD.
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