Progress 07/10/03 to 12/31/07
Outputs
OUTPUTS: The invasion of West Nile virus [WNV] into areas of California previously supporting consistent, inconsistent and no St. Louis encephalitis virus [SLEV] transmission provided a unique natural experiment to test the hypothesis that similarities in natural history among closely related flaviviruses within the Japanese encephalitis serocomplex precludes concurrent sympatric amplification. Results of research to test our overall hypothesis was summarized in the following specific aims: 1. WNV invaded California in 2003 through the SE deserts and then dispersed to every county during 2004. Transmission dynamics and epidemiology differed among cool maritime, hot desert and inland agricultural ecosystems having different avian host populations, especially clustered popualtions of American crows. 2. A degree-day temperature model for WNV replication within Culex tarsalis was generated through alboratory studies and allowed us to compare the rate of viral replication [duration of the
extrinsic incubation period] and the duration of the transmission season in different environments. 3. WNV invasion and persistence was affected by a variety of factors including vector and host competence, cross protective immunity to SLEV, and mechanisms of interseasonal persistence including vertical transmission in mosquitoes and chronic infections in birds. Results were disseminated through research publications, an annual symposium presented at the Conference of the Mosquito and Vector Control Association of California, and presentations at other professional societies include Society for Vector Ecology, American Society of Tropical Medicine and Hygiene, Entomological Society of America, and American Mosquito Control Association.
PARTICIPANTS: W Reisen PI, A Brault co-PI, H Lothrop, Specialist Entomologist, M Kennsington, Lab Assist, B Carroll, Lab Assist, V Martinez, Lab Assist [retd], S Hallam, Lab Assist, Y Fang, Staff Research Assoc, Lab Manager, S Garcia, SRA, J Jones, Student worker, S Wheeler, V Armijos and J Wilson were Staff Research Associates that have transitioned into PhD programs that are on-going. Partner Organizations: Coachella Valley MVCD, Greater LA Co. VCD, Kern MVCD, Sacramento-Yolo MVCD, California Department of Public Health
TARGET AUDIENCES: Mosquito and Vector Control agencies in California California, Department of Public Health
PROJECT MODIFICATIONS: none
Impacts
Our research delineated maintenance, amplification and outbreak transmission cycles in California and determined which mosquito vectors and avian hosts were important. These data were critical in developing surveillance programs and focusing control efforts through enhance decision support.
Publications
- Armijos V, Wheeler SS, Fang Y, Garcia S, Wright SA, Kelley K, Reisen WK. 2007. Are Ardeid colonies nesting over dry land a source of West Nile virus amplification? Proc Mosq Vector Control Assoc Calif 75:7-8.
- Carroll BD, Takahashi RM, Reisen WK. 2007. West Nile Virus Activity in Kern County During 2006. Proc Mosq Vector Control Assoc Calif 75:17-22.
- OConnor P, Wilson JL, Spoehel J, Kluh S, Morales H, Madon MB. 2007. West Nile virus Foci in Greater Los Angeles County Vector Control District, 2003 - 2006. Proc Mosq Vector Control Assoc Calif 75:14.
- Reisen WK, Brault AC, Martinez VM, Fang Y, Simmons K, Garcia S, Omi-Olsen E, Lane RS. 2007. Ability of transstadially infected Ixodes pacificus (Acari: Ixodidae) to transmit West Nile virus to song sparrows or western fence lizards. J Med Entomol 44:320-327.
- Reisen WK, Brault AC. 2007. West Nile virus in North America: perspectives on epidemiology and intervention. Pest Management Sci 63:641-646.
- Reisen WK, Hahn DC. 2007. Comparison of immune responses of brown-headed cowbird and related blackbirds to west nile and other mosquito-borne encephalitis viruses. J Wildl Dis 43:439-449.
- Reisen WK, Brault AC, Martinez VM, Fang Y, Simmons K, Garcia S, Omi-Olsen E, Lane RS. 2007. Ixodes pacificus is not a competent vector of West Nile virus. Proc Mosq Vector Control Assoc Calif 75:34-35.
- Reisen WK, Lothrop HD, Wheeler SS, Kensington M, Gutierrez A, Fang Y, Garcia S, Lothrop B. 2008. Persistent West Nile virus transmission and the displacement St Louis encephalitis virus in southeastern California, 2003-2006. J Med Entomol [in press].
- Reisen WK, Fang Y, Brault AC. 2008. Limited temporal variation in mosquito (Diptera: Culicidae) and avian host competence for western equine encephalomyelitis virus (Togaviridae: Alphavirus). Am J Trop Med Hyg in press
- Wheeler SS, Armijos MV, Garcia S, Fang Y, Reisen WK. 2007. Migratory birds and the spread of encephalitis viruses in California: 10 years of data from the Coachella Valley. Proc Mosq Vector Control Assoc Calif 75:4-6.
- Reisen WK, Fang Y. 2007. Does feeding on infected mosquitoes (Diptera: Culicidae) enhance the role of song sparrows in the transmission of arboviruses in California? J Med Entomol 44:316-319.
- Reisen WK, Fang Y, Martinez V. 2007. Is nonviremic transmission of West Nile virus by Culex mosquitoes (Diptera: Culicidae) nonviremic? J Med Entomol 44:299-302.
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Progress 01/01/06 to 12/31/06
Outputs
Principal Research Accomplishments, 1 Oct 05 - 30 Sep 06 The invasion of West Nile virus [WNV] into areas of California previously supporting consistent, inconsistent and no St. Louis encephalitis virus [SLEV] transmission provided a unique natural experiment to test the hypothesis that similarities in natural history among closely related flaviviruses within the Japanese encephalitis serocomplex preclude concurrent sympatric amplification. Accomplishments during 2005-2006 are summarized below: 1. Epidemiology and ecology of WNV invasion into 4 biomes of California. a. SLEV was not detected in California for the 3rd sequential transmission season. A partial explanation may have been elucidated by our cross immunity studies in House finches that showed that previous infection with WNV provides sterilizing immunity against SLEV. In contrast, previous infection with SLEV protected against mortality and lowered the viremia response, but not to a level precluding mosquito
infection. b. WNV enzootic and epidemic activity varied among our four sampling areas. Activity was low in Coachella Valley and Los Angeles, elevated again in Kern County and in Yolo County. Analyses to elucidate these varied patterns of persistence are on-going. c. Ardeid birds communally nesting in Eucaplyptus trees near Davis in Yolo County were a focus of elevated WNV activity, contrasting our earlier observations in Imperial County where nesting colonies exploited trees over water. These observations support our notion that Cx. tarsalis do not frequently hunt blood meals over water and that landscape rather than host preference may dictate blood feeding and transmission patterns. 2. Temperature models. Nationally, WNV activity tracked above normal temperatures throughout the west [California, Idaho, Dakotas, Nebraska], supporting our published results that indicated that WNV, like SLEV, requires warm weather for amplification. 3. Factors affecting invasion a. Previous
experimental infection studies indicated that transient N-S migrants [Orange-crowned warbler, Yellow warbler, Common yellowthroat] were competent hosts for WNV, however, testing of over 500 samples during the spring of 2006 failed to detect current or previous infection; results similar to previous years. b. Previous vector competence studies showed that Cx. stigmatosoma was the most susceptible species to oral infection, followed by Cx. tarsalis, Cx. quinquefasciatus and Cx. pipiens, but that virus dose-infection curves failed to show a trend over time. During 2006 Cx. quinquefasciatus infection and transmission rates increased noticeably, perhaps increasing the receptivity of these sites for WNV resurgence. c. Alternative WNV transmission cycles involving mammals and Aedes and Culiseta mosquitoes have not been detected, even though dead tree squirrels frequently are found. Ixodes ticks were found to be incompetent hosts for WNV.
Impacts
Our ecological studies have monitored 3 phases of the invasion process of WNV into California [introduction, amplification and subsidence] and identified parallel rural and urban transmission cycles of WNV. Epidemic transmission is initiated within rural and peri-urban landscapes in a Culex tarsalis perimdomestic passerine bird cycle but seems to require infectious American crows to effectively drive WNV into Cx. quinquefasciatus and humans. Search for alternative cycles among mammalian hosts and Aedes mosquito or Ixodid tick vectors have produced negative results, indicating that Culex function as both maintenance and bridge vectors. Epidemic transmission in Los Angeles subsided abruptly after passerine seroprevalence rates exceeded 30%. The force of transmission was maintained by avian virulence because vectors remained largely incompetent and required high viremias for efficient infection. In southern California over wintering seemed to be accomplished by a
combination of continued transmission, vertical passage of virus via infected eggs and chronic infections in birds. Degree-day temperature models developed for the growth of virus within the mosquito host clearly indicated that climate variation drives transmission, with most epidemics occurring during the warmest time of the year and during years with above normal temperature.
Publications
- Fang Y, Reisen WK. 2006. Previous infection with West Nile or St. Louis encephalitis viruses provides cross protection during reinfection in house finches. Am J Trop Med Hyg 75:480-485. Hull J, Hull A, Reisen WK, Fang Y, Ernst H. 2005. Variation in West Nile Virus Antibody Prevalence in Free-ranging California Raptors. The Condor 108: 435-439.
- Lothrop HD, Kensington M, Gutierrez A, Lothrop B, Reisen WK. 2006. West Nile Virus Surveillance in the Imperial and Coachella Valleys, 2005. Proc Mosq Vector Control Assoc Calif 74:[in press].
- Padgett K, Reisen WK, Kahl-Purcell N, Fang Y, Cahoon-Young B, Carney R, Anderson NL, Zucca L, Woods L, Husted S, Kramer VL. 2006. West Nile virus infection in tree squirrels (Rodentia: Scuridae) in California, 2004-2005. Am J Trop Med Hyg [in press].
- Reisen WK, Lothrop HD, Wilson J, Martinez VM, Fang Y. 2006. Field evidence for vertical transmission of West Nile virus. Proc Mosq Vector Control Assoc Calif 74:24-26.
- Reisen WK, Martinzez VM, Fang Y. 2006. Does feeding on infected mosquitoes [Diptera: Culicidae] enhance the role of Song sparrows [Melospiza melodia] in the transmission of arboviruses in California? J Med Entomol [in press].
- Reisen WK, Hahn CS. 2006. Comparison of the immune responses of Brown-headed cowbirds and related blackbirds to West Nile and other mosquitoborne encephalitis viruses. J Wildl Dis [in revision].
- Reisen WK, Martinez VM, Fang Y, Garcia S, Ashtari S, Wheeler SS, Carroll BD. 2006. Role of California (Callipepla californica) and Gambel's (Callipepla gambelii) Quail in the Ecology of Mosquito-Borne Encephalitis Viruses in California, USA. Vector Borne Zoonotic Dis 6:248-260.
- Reisen WK, Brault AC. 2006. West Nile virus in North America: perspectives on epidemiology and intervention. Pesticide Managment Sci [in press].
- Reisen WK, Barker CM, Carney R, Lothrop HD, Wheeler SS, Wilson JL, Madon MB, Takahashi R, Carroll B, Garcia S, Fang Y, Shafii M, Kahl N, Ashtari S, Kramer V, Glaser C, Jean C. 2006. Role of corvids in epidemiology of West Nile virus in southern California. J Med Entomol 43:356-367.
- Reisen WK, Fang Y, Lothrop HD, Martinez VM, Wilson J, OConnor P, Carney R, Cahoon-Young B, Shafii M, Brault AC. 2006. Overwintering of West Nile virus in Southern California. J Med Entomol 43:344-355.
- Reisen WK, Brault AC, Martinez VM, Fang Y, Simmons K, Garcia S, Omi-Olsen E, Lane RS. 2006. Ability of transstadially infected Ixodes pacificus (Acari: Ixodidae) to transmit West Nile virus to Song sparrows or Western fence lizards. J Med Entomol [in press].
- Trevejo RT, Reisen WK. 2006. Comparative attractiveness of two chicken breeds to mosquitoes in southern California. J Am Mosq Control Assoc 22:37-41.
- Wheeler SS, Reisen WK, Yamamoto S, Fang Y, Garcia S, Wright SA, Armijos V. 2006. Role of Ardeid Birds in the Spread of WNV. Proc Mosq Vector Control Assoc Calif 74:[in press].
- Wilson JL, Reisen WK, Madon MB. 2006. Three Years of West Nile virus in Greater Los Angeles County. Proc Mosq Vector Control Assoc Calif 74:9-11.
- Armijos V, Brault AC, Wheeler SS, Fang Y, Langevin S, Wanichaya N, Wright SA, Reisen WK. 2006. Preliminary findings of a Fort-Morgan-like alphavirus from Cliff Swallow bugs [Oeciacus vicarius (Hemiptera:Cimididae)] in Sacramento County. Proc Mosq Vector Control Assoc Calif 74:82-83.
- Barker CM, Reisen WK. 2006. Invasion of California by West Nile virus: role of Corvids. Proc Calif Mosq Vector Control Assoc 74:27-28. Fang Y, Martinez VM, Reisen WK. 2006. WNV Interactions with SLEV: Partial Cross Protective Immunity in House Finches. Proc Mosq Vector Control Assoc Calif 74:23.
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Progress 01/01/05 to 12/31/05
Outputs
Studies on the ecology of WNV at 4 differing biomes described a repeated three phase pattern of WNV introduction, amplification to epidemic levels, and then subsidence. In the SE Californian deserts, enzootic transmission remained localized at marsh habitat along the Salton Sea during 2003 - 2004, but amplified in residential communities near Palm Springs during 2005. In Los Angeles, elevated avian `herd immunity' was associated with the interruption of epidemic transmission in 2004 and inhibited amplification during 2005. In Kern County, enzootic and epidemic transmission persisted at similar levels during 2004 and 2005. The epicenter shifted from southern California to Sacramento during 2005. The invasion of different southern California landscapes enabled us to study the impact of differing Corvid populations on the force of transmission. Infection rates in Cx. tarsalis and sentinel chickens were statistically similar among sites, whereas infection rates in Cx.
quinquefasciatus were statistically higher in areas with elevated Corvid populations. Spatial analyses of dead Corvids showed that the incidence of human and Cx. quinquefasciatus infection was significantly greater within Corvid clusters than without, indicating their importance as a risk factor for human infection. The median time from Cx. tarsalis imbibing an infectious blood meal until transmission (EIP) decreased as a function of temperature, requiring 109 DD with a zero development point of 14.3C. Enzootic WNV activity commenced only the duration of the EIP decreased and virus potentially was transmitted within ≤2 gonotrophic cycles. Infection of two birds species with a dilution series of WNV indicated that there was no threshold for infection, so that the wide-range of virus expectorated by blood feeding mosquitoes would have little impact on resulting infection. Transient N-S migrants were competent hosts and could provide effective short term dispersal for WNV. Winter
residents were competent hosts and readily infected Cx. tarsalis that fed upon them. Song sparrows were a competent host when infected by inoculation, but could not be infected orally after feeding on 1 - 20 infected mosquitoes. House finches infected initially with either WNV or SLEV were protected against homologous or heterologous challenge; prior infection with WNV provided sterilizing immunity, whereas prior infection with SLEV prevented viremia from SLEV, but only reduced WNV viremias. In our 4 study areas, Cx. stigmatosoma was most susceptible to oral infection with WNV, followed by Cx. tarsalis and then Cx. pipiens. There did not seem to be a marked change in susceptibility to infection to either WNV or SLEV over time following the introduction of WNV. WNV may have persisted in southern California during the winter by continued transmission to corvids, vertical transmission in Cx. quinquefasciatus and Cx. tarsalis or chronic infection in a variety of avian species.
Impacts
Our ecological studies have monitored 3 phases of the invasion process of WNV into California [introduction, amplification and subsidence] and identified parallel rural and urban transmission cycles of WNV in southern California. Epidemic transmission in urban landscapes seems to require infectious American crows to introduce virus into neighborhoods and susceptible passerines to maintain and amplify these introductions. Infection rates in Cx. quinquefasciatus and humans were highest within statistically defined clusters of dead American crows; however, epidemic transmission subsided abruptly after passerine seroprevalence rates exceeded 30%. The force of transmission was maintained by avian virulence because vectors remained largely incompetent and required high viremias for efficient infection. In southern California over wintering seemed to be accomplished by a combination of continued transmission, vertical passage of virus via infected eggs and chronic infections
in birds. Degree-day temperature models developed for the growth of virus within the mosquito host clearly indicated that climate variation drives transmission, with most epidemics occurring during the warmest time of the year and during years with above normal temperature.
Publications
- Reisen WK, Fang Y, Martinez VM. 2004. Avian and mosquito host competence for West Nile virus. Proc Mosq Vector Control Assoc Calif 72:18-20. Reisen WK, Fang Y, Martinez VM. 2005. Avian host and mosquito (Diptera: Culicidae) vector competence determine the efficiency of West Nile and St. Louis encephalitis virus transmission. J Med Entomol 42:367-375.
- Reisen WK, Fang Y, Martinez VM. 2005. Vector and host competence: importance of virulence in birds for WNV transmission. Proc Mosq Vector Control Assoc Calif 73:28-31.
- Reisen WK, Wheeler SS, Yamamoto S, Fang Y, Garcia S. 2005. Nesting ardeid colonies are not a focus of elevated West Nile virus activity in southern California. Vector Borne Zoonotic Dis 5:258-266.
- Reisen WK, Fang Y, Martinez VM. 2006. Effects of temperature on the transmission of West Nile virus by Culex tarsalis (Diptera: Culicidae). J Med Entomol [in press].
- Reisen WK, Fang Y, Lothrop HD, Martinez VM, Wilson J, O'Connor P, Carney R, Cahoon-Young B, Shafii M, Brault AC. 2006. Overwintering of West Nile virus in California. J Med Entomol [in press].
- Reisen WK, Barker CM, Carney R, Lothrop HD, Wheeler SS, Wilson JM, Madon MB, Takahashi R, Carroll B, Garcia S, Fang Y, Shafii M, Kahl N, Ashtari S, Kramer VL, Glaser C, Jean C. 2006. Role of Corvids in the epidemiology of West Nile virus in Southern California. J Med Entomol [in press].
- Armijos V, Wright SA, Reisen WK, Kelly K, Yamamoto S, Brown DA. 2005. West Nile Virus in Sacramento and Yolo Counties, 2004. Proc Calif Mosq Control Assoc 73:24-27.
- Goddard LB, Roth A, Reisen WK, Scott TW. 2003. Extrinsic incubation period of West Nile virus in four California Culex (Diptera: Culicidae) species. Proc Mosq Vector Control Assoc Calif 71:70-75.
- Goddard LB, Roth AE, Reisen WK, Scott TW. 2003. Vertical transmission of West Nile Virus by three California Culex (Diptera: Culicidae) species. J Med Entomol 40:743-746.
- Lothrop HD, Kensington M, Gutierrez A, Lothrop B, Reisen WK. 2005. West Nile Virus Surveillance in the Imperial and Coachella Valleys, 2005. Proc Mosq Vector Control Assoc Calif 73:9-11.
- Takahashi RM, Reisen WK, Barker CM. 2005. Invasion of Kern County by West Nile virus. Proc Mosq Vector Control Assoc Calif 73:20-23. Wheeler SS, Reisen WK, Chiles RE. 2004. West Nile infections in free ranging wild birds in the Coachella Valley, Riverside Co., California. Proc Mosq Vector Control Assoc Calif 72:12-14.
- Wheeler SS, Carney R, Carroll B, Wright SA, Armijos V, Wilson J, Garcia S, Fang Y, Reisen WK. 2005. West Nile Virus and Wild Birds: Who Lives and Who Dies? Proc Mosq Vector Control Assoc Calif 73:32-37.
- Wilson J, Madon MB, Reisen WK. 2005. The overwitnering and amplification of West Nile in the southern portion of Greater Los Angeles Vector Control Districxt. Proc Mosq Vector Control Assoc Calif 73:12-13.
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Progress 01/01/04 to 12/31/04
Outputs
Epidemiology and ecology of WNV invasion. After introduction during 2003, West Nile virus [WNV] successfully over wintered in the Coachella Valley. Enzootic amplification was confined to wetlands along the Salton Sea and spread to upland residential communities was limited. St Louis encephalitis virus [SLEV] was not detected in mosquitoes or sentinel chickens, perhaps indicating that extensive transmission of WNV prevented the amplification of this closely related flavivirus. WNV invaded the Los Angeles basin during fall 2003, over wintered as detected by continued American crow death during winter, and then amplified to epidemic levels during the following spring and summer. Transmission subsided during late summer, perhaps in association with acquired immunity and/or depopulation of bird host populations. The principal vector in Los Angeles was Cx. p. quinquefasciatus, but infections also were found repeatedly in Cx. tarsalis and Cx. stigmatosoma. WNV dispersed to
the Central Valley during midsummer 2004 and amplified in Kern County. Amplification was associated with death and immunity in Western scrub jays and to a lesser extent American crows. Cx. tarsalis was involved in rural transmission, whereas Cx. p. quinquefasciatus was involved in both rural and urban transmission. WNV rapidly dispersed north to our study areas in the Sacramento area where it became established at low levels during late summer. Factors affecting invasion. Host competence studies showed that Western scrub jays were most the most competent host [highest viremia] of those species infected, followed in descending order by House finches and House sparrows. Mourning doves, Common ground doves, California quail and domestic chickens appeared to be relatively incompetent hosts. Vector competence studies showed that Cx. stigmatosoma was the most susceptible species to oral infection, followed by Cx. tarsalis, Cx. p. quinquefasciatus and Cx. pipiens. Most mosquitoes were
relatively refractory to infection as compared to endemic SLEV, indicating that high virulence to avian hosts is important in vector infection. Requirement of a high oral dose for infection agrees well the focality of amplification in relation to corvid populations that are susceptible and produce very elevated viremias. Invading WNV may differ markedly from endemic SLEV in that critical vertebrate hosts must produce elevated viremias that frequently results in death. Previous infection with SLEV provided protective but not sterilizing immunity following challenge with WNV. Viremia titers were lower than positive controls. In contrast, previous infection with WNV provided protective and sterilizing immunity following challenge with SLEV and may be a contributing factor in the disappearance of SLEV in southern California during 2004. Experimental studies have documented vertical, transstadial and venereal transmission of WNV by Cx. tarsalis, albeit at low rates. These modes of
transmission may be sufficient to allow overwintering of virus within mosquito populations.
Impacts
Our research has successfully tracked the invasion of California by West Nile virus from initial entry into the southeastern deserts through Los Angeles and then into the Central Valley. Parallel rural and urban transmission cycles were described and surveillance methods evaluated to track enzootic virus activity within these very different environments and host systems. Avian host and mosquito vector competence experiments have described the importance of virulence and resulting high viremias in passerine birds in transmission dynamics, virus distribution and epidemic amplification.
Publications
- Reisen WK, Lothrop HD, Chiles RE, Madon MB, Cossen C, Woods L, Husted S, Kramer VL, Edman JD. 2004. Invasion of California by West Nile Virus. Emerg Infect Dis 10:1369-1378.
- Reisen WK, Y Fang and VM Martinez. 2005. Avian host and vector competence determine the efficiency of West Nile virus transmission dynamics. J. Med. Entomol. [in press]
- Reisen WK, Fang Y, Martinez VM. 2004. Avian and mosquito host competence for West Nile virus. Proc Mosq Vector Control Assoc Calif 72:18-20.
- Reisen WK, Wheeler SS, Yamamoto S, Fang Y, Garcia S. 2005. Role of communally nesting ardeid birds in the ecology of West Nile virus in Southern California. Vector Borne Zoonotic Dis submitted.
- Wheeler SS, Reisen WK, Chiles RE. 2004. West Nile infections in free ranging wild birds in the Coachella Valley, Riverside Co., California. Proc Mosq Vector Control Assoc Calif 72:12-14.
- Wilson J, Hazelrigg JE, Reisen WK, Madon MB. 2004. Invasion of Greater Los Angeles by West Nile virus - 2003. Proc Mosq Vector Control Assoc Calif 72:6-11.
- Chiles RE, Green EN, Fang Y, Goddard L, Roth A, Reisen WK, Scott TW. 2004. Comparison of in situ enzyme immunoassay, RT-PCR and the VecTest wicking assay to detect West Nile and St. Louis encephalitis viruses in a blinded laboratory evaluation. J Med Entomol 41:539-544.
- Chiles RE, Green EN, Fang Y, Reisen WK, Edman JD, Brault AC. 2004. Surveillance for arboviruses in California mosquito pools: Current and future protocols. Proc Mosq Vector Control Assoc Calif 72:15-17.
- Hom A, Houchin A, McCaughey K, Kramer VL, Chiles RE, Reisen WK, Tu E, Glaser C, Cossen C, Baylis E, Eldridge BF, Sun B, Padgett K, Woods L, Marcus L, Hui LT, Castro M, Husted S. 2004. Surveillance for msoquito-borne encephalitis activity and human disease, including West Nile virus in California, 2003. Proc Mosq Vector Control Assoc Calif 72:48-54.
- Lothrop HD, Kensington M, Reisen WK. 2004. Invasion of California by West Nile virus, 2003: Imperial and Coachella Valleys. Proc Mosq Vector Control Assoc Calif 72:3-6.
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Progress 01/01/03 to 12/31/03
Outputs
The overall objective of our research is to monitor the invasion of California by West Nile virus [WNV] and to investigate factors associated with its efficient persistence, dispersal and amplification at study areas established in irrigated desert [Imperial and Coachella Valleys], urban [Los Angeles County] and Central Valley [Kern and Sacramento Counties] habitats. WNV was detected initially along the southern shore of the Salton Sea and then moved north into wetlands in the Coachella Valley where it was effectively tracked by isolation from Cx. tarsalis and seroconversions in sentinel chickens. Virus then skipped to Riverside and then into the Whittier Area of Los Angeles where dead birds were clustered near a large crow roost and isolations were made from pools of Cx. pipiens quinquefasciatus. WNV then moved down the I-15 corridor into San Diego. Vector competence studies indicated that California populations of Cx. tarsalis, Cx. stigmatosoma and Cx. pipiens
quinquefasciatus were more susceptible to infection that eastern populations of Cx. pipiens but required higher virus doses for infection than with St. Louis encephalitis virus. Avian host competence studies showed that California house finches and mourning doves were susceptible to infection at very low infectious doses. House finches and Western scrub jays succumbed to infection, whereas brown headed cowbirds, Brewer's blackbirds, common ground doves, mourning doves and valley quail survived. Cross-immunity studies in house finches indicated that previous infection with SLEV provided partial protection from infection with WNV. Birds surviving infection frequently showed chronic infection at necropsy detected by RT-PCR and virus isolation after blind passage in mosquito cell lines.
Impacts
Our studies documented which surveillance methods worked best in different habitats to track the invasion of WNV into California and provided insight into mosquito and bird host competence for this virus
Publications
- Barker CM, Reisen WK, Kramer VL. 2003. California State Mosquito-borne Virus Surveillance and Response Plan: retrospective evaluation using conditional simulations. Am J Trop Med Hyg 68:508-518.
- Barker CM, Reisen WK, Kramer VL. 2003. Enhanced arbovirus surveillance: retrospective evaluation of the California State Mosquito-borne Virus Surveillance and Response Plan. Proc Mosq Vector Control Assoc Calif 71:44-48.
- Goddard L, Roth A, Reisen WK, Scott TW. 2003. Vertical transmission of West Nile virus by Culex species. J Med Entomol 40:743-746.
- Goddard L, Roth A, Reisen WK, Scott TW. 2003. Extrinsic incubation period of West Nile virus in four California Culex (Diptera: Culicidae) species. Proc Mosq Vector Control Assoc Calif 71:70-75.
- McCaughey K, Miles SQ, Woods L, Chiles RE, Hom A, Kramer VL, Jay-Russel M, Sun B, Reisen WK, Scott TW, Hui LT, Steinlein DB, Castro M, Houchin A, Husted S. 2003. The California West Nile virus dead bird surveillance program. Proc Mosq Vector Control Assoc Calif 71:38-43.
- Reisen WK, Chiles RE, Green EN, Fang Y, Mahmood F. 2003. Previous infection protects finches from re-infection with St. Louis encephalitis virus. J Med Entomol 40:300-305.
- Reisen WK, Chiles RE, Green EN, Fang Y, Mahmood F, Martinez VM, Laver T. 2003. Effects of immunosuppression on encephalitis virus infection in the house finch, Carpodacus mexicanus. J Med Entomol 40:206-214.
- Reisen WK, Lothrop HD, Lothrop B. 2003. Factors affecting the outcome of mark-release-recapture studies with Culex tarsalis (Diptera: Culicidae). J Med Entomol 40:820-829.
- Reisen WK, Chiles RE, Fang Y, Green EN, Martinez VM, Carroll B. 2003. Host competence of avian species for encephalitis viruses in California. Proc Mosq Vector Control Assoc Calif 71.
- Reisen WK, Chiles RE, Martinez VM, Fang Y, Green EN. 2003. Experimental infection of California birds with western equine encephalomyelitis and St. Louis encephalitis viruses. J Med Entomol 40:968-982.
- Reisen WK, Chiles RE, Martinez VM. 2003. Encephalitis virus persistence in California birds: effects of viral dose on house finch (Carpodacus mexicanus) infection. J Med Entomol [submitted].
- Reisen WK, Chiles RE, Martinez VM, Green EN, Fang Y. 2003. Encephalitis virus persistence in California birds: failure to detect chronic infections in mourning doves (Zenaidura macroura ). J Med Entomol [in press].
- Reisen WK. 2003. Use of meterological data to predict mosquito-borne encephalitis risk in California: preliminary observations in Kern County. Proc Internat Congr Ecosystem Hlth.
- Steinlein DB, Husted S, Reisen WK, Kramer VL, Chiles RE, Glaser C, Cossen C, Tu E, Gilliam S, Hui LT, Eldridge BF, Boyce K, Yamamoto S, Webb JP, Lothrop HD, Fujioka K, Brisco A, Russell MJ, Houchin A, Castro M, Hom A, Miles SQ, Rogers C, Cornelius A, McCaughy K, Kohlmeier K, Scott TW. 2003. Summary of mosquito-borne encephaltiis virus surveillance in California: 1998-2002. Proc Mosq Vector Control Assoc Calif 71:17-27.
- Wheeler S, Reisen WK, Chiles RE. 2003. Wild bird arboviral surveillance in the Coachella Valley, California. Proc Mosq Vector Control Assoc Calif 71:49-50.
- Husted S, Kramer VL, Houchin A, Chiles RE, Glaser C, Russell MJ, Reisen WK, Eldridge BF, Cossen C, Tu E, Scott TW, McCaughy K, Reeves WC, Castro M, Hom A, Hui LT. 2003. Surveillance for mosquito-borne encephalitis virus activity and human disease in California, 2002. Proc Mosq Vector Control Assoc Calif 71:28-37.
- Lothrop HD, Lothrop B, Reisen WK. 2003. Evaluations of barrier spray using formulations of pyrethrin and pyrethroid insecticides. Proc Mosq Vector Control Assoc Calif 71:13-16.
- Mahmood F, Chiles RE, Fang Y, Barker CM, Reisen WK. 2003. Host competence of nestling birds for western equine encephalomyelitis and St. Louis encephalitis viruses. J Med Entomol [submitted].
- Mahmood F, Fang Y, Green EN, Clark S, Reisen WK. 2004. Evaluation of methods for studying the vector competence of Culex tarsalis for western equine encephalomyelitis virus. J Am Mosq Control Assoc [in press].
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