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Am. J. Trop. Med. Hyg., 78(4), 2008, pp. 681-686
Copyright © 2008 by The American Society of Tropical Medicine and Hygiene

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Limited Interdecadal Variation in Mosquito (Diptera: Culicidae) and Avian Host Competence for Western Equine Encephalomyelitis Virus (Togaviridae: Alphavirus)

William K. Reisen*, Ying Fang, AND Aaron C. Brault
Arbovirus Research Unit, Center for Vectorborne Diseases, Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, California

Historically, western equine encephalomyelitis virus (WEEV) caused large equine and human epidemics in the Americas from Canada into Argentina. Despite recent enhanced surveillance for West Nile virus, there have been few reports of equine or human cases and little documented enzootic activity of WEEV. During the past three years, WEEV has been active again in California, but without human or equine cases. In the current study, we compared host and vector competence of representative WEEV isolates made during each decade over the past 60 years using white-crowned sparrows, house sparrows, and Culex tarsalis Coquillett as representative hosts. Results indicated limited time-related change in virulence among WEEV strains in birds and little difference in vector competence in Cx. tarsalis. Although temporal and spatial genetic changes have been documented, these seem to present limited phenotypic change in host competence and cannot explain the absence of equine and human cases.

Received November 10, 2007. Accepted for publication January 26, 2008.

Acknowledgments: We thank Sandra Garcia (Arbovirus Research Laboratory), and Vincent Martinez, Brian Carroll, and Scott Hallam (Arbovirus Field Station, Center for Vectorborne Diseases) for excellent technical assistance in the laboratory and field, respectively.

Financial support: This study was supported, in part, by research grants RO1-39483, RO1-AI47855, and RO1-AI55607 from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, the Coachella Valley and Kern Mosquito and Vector Control Districts, and by special funds for the Mosquito Research Program allocated annually through the Division of Agriculture and Natural Resources, University of California.

* Address correspondence to: William K. Reisen, Center for Vector-borne Diseases, University of California, Old Davis Road, Davis, CA 95616. E-mail: arbo123{at}pacbell.net

Authors’ address: William K. Reisen, Ying Fang, and Aaron C. Brault, Center for Vectorborne Diseases, University of California, Old Davis Road, Davis, CA 95616, Telephone: 530-752-0124, E-mail: arbo123{at}pacbell.net.






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Copyright © 2008 by the American Society of Tropical Medicine and Hygiene.