Progress 06/15/04 to 06/14/07
Outputs
In cooperation with several mosquito abatement districts in Cook Co., IL, approximately 11,000 mosquito pools (nearly 40,000 mosquitoes) were tested for West Nile virus (WNV) in the past year. Nearly 1,800 pools, primarily Culex restuans and Cx. pipiens, were positive. Approximately 400 birds were tested for WNV-antibodies using ELISA, and more than 17% were positive. Infection rates in Culex species collected in Cook County were relatively high over extended periods in 3 of the past 5 years. Prevalence ranged from 4-14% WNV positive for 2-4 weeks of the season. Temperature appeared to be the major regulator of transmission intensity and the increase in infected mosquito pools paralleled the increase in Cx. pipiens abundance. Studies comparing temporal change in vector abundance, infection rate, and human cases by onset date, showed that density of infected mosquitoes was the best indicator of risk to humans, and changes in density tended to precede and parallel
changes in human cases by 2-3 weeks. Spring bird counts and breeding bird surveys throughout Illinois showed declines in populations of corvids and some cavity nesters in areas with high WNV transmission in mosquitoes and humans. Birds contaminated feeders with low levels of WNV. In Cook Co., abundance of Cx. pipiens was greater than in Central Illinois and numbers tended to build up faster in Cook Co., which may reflect higher temperatures in suburban "heat islands" and more underground winter refuges. Recent tests of samples suggest an increase in the discontinuity between VecTests and TaqMan, possibly reflecting local variation in WNV antigenic properties and nucleic acid sequences. Bloodmeal analysis and seroprevalence studies implicated the same avian species as major hosts; American robins, northern cardinals, mourning doves, and house sparrows. The rank in seroprevalence, however, did not necessarily agree with the rank in blood meals. American robins, for example, outnumbered
the other species in the blood meal analysis, but not in seroprevalence. The proportion of mammal vs. bird bloods varied spatially based on abundance of available hosts in the area. Mosquito traps near or in horse stables, cow barns, or pig stables had almost 20% feeding on mammals, whereas blooded mosquitoes caught in residential/campus areas had less than 7% mammal blood. One crow blood and one human blood were found in 50 blood meals identified to species, indicating these species were low preference. In Central Illinois, both molecular analysis and morphology of male reproductive structures showed that hybrids of Cx. pipiens with Cx. quinquefasciatus occur in Champaign-Urbana in August and September. This area is usually considered outside the northern boundary of the hybrid zone. The start of mosquito breeding was early, March and April 2007 in Central Illinois, and early season Cx. restuans were RT-PCR positive. This suggests overwintering Cx. restuans may be the initial source
of enzootic transmission. WNV was not detected in overwintering Cx. pipiens (0 positives out of approx. 3,500 mosquitoes collected from stormwater tunnels).
Impacts
These data challenge several previous conclusions: 1) No late season increase in mammal feeding was found as reported for the East Coast. 2) The blood-feeding pattern must be expressed in terms of both temporal change and spatial availability of hosts; proportion of mammal feedings varies. 3) Decline in WNV transmission tends to begin in early Aug., corresponding to the end of breeding season for common urban mosquito species. 4) Crows are not essential for WNV amplification. 5) Extended collection of egg rafts in Central Illinois when photoperiod is reduced to > 14 hours of light is probably due to the presence of Cx. pipiens complex hybrids that lack an ovarian diapause. A similar late season oviposition pattern was noted for Cook Co, but is unlikely due to Cx. quinquefasciatus hybrids because the location is beyond the hybrid zone. 6) These studies suggest that density of infected mosquitoes is a better indicator of risk than the number of infected biting mosquitoes
x mammal feeding preference x vector competency. 7) These studies provide first evidence that Cx. restuans overwinters the virus in Illinois. 8) Preliminary data suggest the vast underground stormwater/sewage system is responsible for the timing and abundance of Cx. pipiens in Cook Co. These studies established basics of the urban transmission cycle in central and northern IL, and testable hypotheses can now be developed to elucidate critical determinants of transmission and when intervention might be most efficaceous.
Publications
- Lampman, R.L., Slameck, M., Krasavin, N., Kunkel, K. and Novak, R. 2006. Culex population dynamics and West Nile virus transmission in east-central Illinois. Journal American Mosquito Control Assoc. 22(3): 390-400.
- Edillo, F.E. , Kiszewski, A., Hutchinson, M., Bugbee, L., Arias, J., Johnson, J., Gaines, D., Halpaus, J., Cuffee, F., Lampman, R. and Novak, R.J., et al. 2006. ABSTRACT: Population structure of the Culex pipiens vectors of West Nile virus in eastern North America. American Journal of Tropical Medicine and Hygiene 75 (5): 173-173 599 Suppl. S, Nov. 2006.
- Gu, W.D. and Novak, R.J. 2006. Statistical estimation of degree days of mosquito development under fluctuating temperatures in the field. Journal of Vector Ecology. 31(1):107-112.
- Ward, M.P., Raim, A., Yaremych-Hamer, S., Lampman, R. and Novak, R.J. 2006. Does the roosting behavior of birds affect transmission dynamics of West Nile virus? American Journal of Tropical Medicine and Hygiene. 75(2):350-355.
- Bunde, J.M., Heske, E.J., Mateus-Pinilla, N.E., Hofmann, J.E. and Novak, R.J. 2006. A survey for West Nile virus in bats from Illinois. Journal of Wildlife Diseases. 42(2):455-458.
- Sanogo, Y.O., Dobson, S.L., Bordenstein, S.R. and Novak, R.J. 2007. Disruption of the Wolbachia surface protein gene wspB by a transposable element in mosquitoes of the Culex pipiens complex (Diptera, Culicidae). Insect Molecular Biology. 16(2):143-154.
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Progress 01/01/06 to 12/31/06
Outputs
We examined spatial and temporal distributions of mosquito infection rates and bird seropositive rates in the vicinity of Champaign-Urbana, Illinois. The main West Nile virus (WNV) vectors were Culex pipiens and Culex restuans, outnumbering detections of all other species by 30 to 100 fold. Culex salinarius and Cx. tarsalis (implicated as major vectors in northeast U.S. and west of the Mississippi River, respectively) were present in low abundance and were only rarely positive for WNV. Numbers of Culex pipiens peaked in August and Cx. restuans peaked in July. Degree-day and maximum temperature models (threshold 27C) predicted Cx. pipiens crossover in 2005 to within a day of observed crossover. The largest number of WNV-antibody positive birds were House Sparrows, Northern Cardinals, American Robins, Mourning Doves, and Gray Catbirds. Analysis of Culex specimens was consistent with the avian seropositive rates, verifying the role of Culex and passerine birds as primary
vectors and hosts. Captures of seronegative bird species suggested either low exposure rate or high mortality rate. The temporal patterns of infection rates in mosquitoes and seropositive rates in birds did not parallel each other, except with juvenile birds, reflecting the confounding nature of seasonal bird dispersal patterns and year-to-year survivorship of antibody positive birds. We are sequencing West Nile Virus strains collected from different location in Illinois. We also designed DNA probes to discriminate between Culex pipiens, Cx quinquefasciatus, Cx restuans and Cx salinarius, the main WNV vectors in Illinois. We have also developed a real-time PCR technique to detect and quantify West Nile Virus vectors, which will help determine the role of each mosquito species in WNV transmission and help target our approach to surveillance and control. In addition to the PCR technique, a new marker derived from Wolbachia bacterium specific to Culex pipiens and Cx. quinquefasciatus was
developed and is being used to study the distribution of the two species in Illinois.
Impacts
These studies help determine which species of mosquitoes are likely vectors of WNV, which helps to target specific control measures. The information on bird infections will aid in assessing morbidity and mortality of Illinois wildlife to WNV, and also to predict which species can serve as bridge vectors of the virus. We showed that the distribution of one vector -- Culex quinquefasciatus -- is expanding north. Moreover, we detected intermediate forms (hybrids) of the two species during the winter. This can have very important health implications because Culex quinquefasciatus -- which bites preferentially mammals including man -- cannot overwinter, whereas Culex pipiens - which feeds mainly on birds -- can overwinter. Their hybrid forms could serve as a bridge vector for the transmission of West Nile virus to humans. Using the DNA probes to discriminate between Culex pipiens, Cx quinquefasciatus, Cx restuans and Cx salinarius will help us understand the dynamics of
the main WNV vectors in Illinois. The study is yielding results that will be of value in mosquito management programs, ensuring that infections of humans can be minimized through science-based management recommendations.
Publications
- Davis, C.T., Ebel, G.D., Lanciotti, R.S., Brault, A.C., Guzman, H., Siirin, M., Parsons, R.E., Beasley, D.W.C., Novak, R.J., Elizondo-Quiroga, D., Green, E.N., Young, D.S., Stark, L.M., Artsob, H., Tesh, R.B., Kramer, L.D. and Barrett, A.D.T. 2005. Phylogenetic analysis of North American West Nile Virus isolates 2001-2004: Evidence for the emergence of a dominant genotype. Virology 342: 252-265.
- Reno, H. and Novak, R.J. 2005. Characterization of a pyrase-like activity in Aedes triseriatus, Aedes hendersoni and Aedes aegypti. American Journal of Tropical Medicine and Hygiene 73: 541-545.
- Jacob, B., Nelson, P.G., Lampman, R., Morris, J., Raim, A., Funes, J., LaPointe, C. and Novak, R. 2005. Comparing GPS technology for identifying spatial ecological variation for urban mosquito management. Wing Beats 16: 30-33.
- Rapaport, A.S., Lampman, R.L. and Novak, R.J. 2006. Evaluation of selected modifications to carbon dioxide and infusion-baited mosquito traps in Urbana, Illinois. Journal American Mosquito Control Association 21: 395-399.
- Kunkel, K.E., Novak, R.J., Lampman, R. and Gu, W.. 2006. Modeling the impact of variable climatic factors on the crossover of Culex restuans and Culex pipiens (Diptera: Culicidae) vectors of West Nile Virus in Illinois. American Journal of Tropical Medicine and Hygiene 74: 168-173.
- Lampman, R.L., Krasavin, N.M., Szyska, M. and Novak, R.J. 2006. A comparison of two West Nile Virus detection assays (TaqMan reverse transcriptase-polymerase chain reaction and VecTest antigen assay) during three consecutive outbreaks in northern Illinois. Journal of American Mosquito Control Association 22: 76-86.
- Beveroth, T.A., Ward, M.P., Lampman, R., Ringia, A. and Novak, R.J. 2006. The changes in seroprevalence of West Nile Virus across Illinois in free-ranging birds from 2001-2004. American Journal of Tropical Medicine and Hygiene 74: 174-179.
- Novak, R.J. and Gerberg, E.J. 2006. Natural-based repellent products: Efficacy for military and general public uses. Journal American Mosquito Control Association, Supplement, Current Trends In Repellent Technology 21: 7-12.
- Gu, W., Lampman, R., Krasavin, N., Berry, R. and Novak, R. 2006. Spatio-temporal analysis of West Nile Virus transmission in Northern Illinois, 2004. Vector-Borne Zoonotic Diseases 6:91-98.
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Progress 01/01/05 to 12/31/05
Outputs
We are comparing seasonal changes in populations of key mosquito species by collecting mosquitoes at selected sites using 5 methods. Multiple sampling methods are used because the efficacy of each method varies by mosquito species, habitat, and physiological state. At each site, mosquitoes are collected for 1-3 days before and during the bird collections in the same area. Collection data are analyzed, in conjunction with meteorological and ecological variables, to determine seasonal trends in regional abundance, indices of mosquito species association, and correlation of key events and temporal events to environmental variables. We are determining abundances of key bird species from northern to southern Illinois from May to September, using surveys in conjunction with bird and mosquito trapping. We are analyzing temporal overlap in host and mosquito abundance and development. Results from the mosquito and host sampling and serology will be added to a statewide
database to help predict disease outbreaks based on samples of hosts and mosquitoes. Sampling and models developed will help estimate the magnitude of the disease, which will be critical for mitigating the incidence of vectors positive for WNV, using appropriate IPM methods in both urban and rural areas, thus helping avert impacts of infection in humans and animals. Sampling of mosquitoes was conducted in 2005 and will continue for the duration of the project. Focused processing of samples by RT-PCR allowed 24-hour turnaround of data and recommendations to mosquito abatement district personnel. Use of RT-PCR as a back-up to the Vec-Test was needed because the Vec-Test kits are adequate for detecting infected mosquitoes, but that approach underestimates recently infected mosquitoes having a low titer of virus. A collaborative study with the Illinois State Water Survey has resulted in a model to predict the rise in Culex pipiens, the main enzootic and suspect epizootic vector of WNV in
Illinois. The prediction for WNV vectors can be found at http://sisyphus.sws.uiuc.edu/research/westnile/index_anim.htm. This model predicts an increasingly early cross-over (50% Cx. pipiens and 50% Cx. restuans abundance in oviposition trap surveys) during warm weather. Cx. pipiens abundance is related to transmission of WNV, which peaks within approximately 2 weeks after cross-over. The long-term project goals are to develop descriptive and quantitative models to predict spatial and temporal interactions of key vector and host populations that influence virus transmission in the state and Midwest.
Impacts
Sampling determines prevalence of West Nile Virus antibodies in different mosquito species as well as in birds, which act as reservoirs for the virus. Our sampling, coupled with the simulation model that we developed, will help managers of mosquito populations understand the incidence of virus infections, allowing them to intervene against mosquitoes in specific areas. Understanding when the cross-over of mosquito species from Cx. restuans to Cx. pipiens occurs allows more-specific management methods to be targeted toward those sites showing the increases in Cx. pipiens.
Publications
- Gu, W. and Novak, R.J. 2005. Habitat-based modeling of impacts of mosquito larval interventions on entomological inoculation rates, incidence and prevalence of malaria. American Journal of Tropical Medicine and Hygiene 73: 546-552.
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Progress 01/01/04 to 12/31/04
Outputs
Sampling of mosquitoes was conducted in 2004 and will continue for the duration of the project. We are using the data to develop a simulation model to quantify seasonal and regional variation in vector abundance and predict transmission cycles. In addition, we are developing a database on the presence of and exposure to West Nile Virus in mosquitoes, birds and mammals. The long-term project goals are to develop descriptive and quantitative models to predict spatial and temporal interactions of key vector and host populations that influence virus transmission in the state and Midwest.
Impacts
Sampling will determine prevalence of West Nile Virus antibodies in different mosquito species as well as in birds, which act as reservoirs for the virus. Our sampling, coupled with simulation models, will help managers of mosquito populations understand the incidence of virus infections, allowing them to intervene against mosquitoes in specific areas, thus reducing the possibility of diseases of humans and animals.
Publications
- Gu, W. and Novak, R. 2004. Detection probability of arbovirus infection in mosquito populations. Am. J. Trop. Med. Hyg. 71: 636-638.
- Gu, W., Lampman, R. and Novak, R. 2004. Assessment of arbovirus vector infection rates using variable size pooling. Medical and Veterinary Entomology 18:200-204.
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