West Nile Virus Information

West Nile virus is a mosquito-borne flavivirus (of the Flaviviridae family of viruses) from Africa, the Middle East, Europe, and Asia that emerged as a pathogen in New York City in the summer of 1999. By winter 2004, human and other animal infections had occurred in Canada, all of the contiguous United States, parts of Mexico and some Caribbean islands. The virus is transmitted to humans and animals by many species of mosquitoes. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days.

West Nile is believed to have infected more than 1 million people in the United States in just the seven years since it first struck the nation, Most people didn't know it because only about one in 5 people develop symptoms, and fewer get the life-threatening disease. Still, West Nile has killed almost 800 people in the U.S. in that time period, and caused severe neurologic illness, meningitis or encephalitis, in more than 8,000. Others are left with polio-like paralysis.

While some federal agencies are researching possible vaccines, keeping records, developing more accurate WNV tests, and producing educational plans and tools, wildlife managers can be found looking at new surveillance techniques for early detection of the disease in local populations of birds.

For example, a new surveillance method to provide an early warning predictor of human WNV activity has been investigated using cliff swallows in the western United States. WNV can be detected in swallows before it is transmitted to local human populations. Because of this, sampling local bird populations could provide an early warning system for humans. Public health officials can use spatial data of virus occurrence to help guide their control efforts. Swallows are a good model for early detection of WNV because they breed in habitats that have high mosquito populations, thus exposing them to high numbers of vectors early in the season. They are abundant and widely distributed, and their nesting colonies occur at almost every overpass and culvert throughout the western United States.

Scientists are also looking at the distribution and susceptibility of small mammals to WNV about which little is known. Raccoons, opossum, white-tailed deer, and squirrels have been tested for WNV, and all showed evidence of high exposure of local populations to the virus. Experimental infection studies can conducted to determine if any of these mammal species are competent reservoirs and/or useful for surveillance. The data will be used in the development of epidemiologic models.
Additionally, wildlife biologists are also studying the effect of WNV in greater sage-grouse, a species likely to be listed by the U.S. Fish and Wildlife Service as a threatened species. The sage grouse has been found to be extremely susceptible to WNV, suffering high mortality rates. This could hamper long-term conservation efforts. However, during recent studies with captive sage grouse, wildlife biologists were able to successfully maintain populations of the birds for extended periods of time and were also able to get some of the birds to reproduce in captivity. This was an unexpected added benefit of WNV studies and could prove useful in the conservation of the species.

Summary above from:

MCLEAN, R. G., L. CLARK, M. R. DUNBAR, K. C. VERCAUTEREN, AND T. A. CAMPBELL. 2005. Wildlife disease research at the APHIS National Wildlife Research Center. Pages 123-135 in Proceedings of the One Hundred and Eighth Annual Meeting of the United States Animal Health Association.
ROOT, J. J., J. S. HALL, R. G. MCLEAN, N. L. MARLENEE, B. J. BEATY, J. GANOWSKI, AND L. CLARK. 2005. Serologic evidence of exposure of wild mammals to flaviviruses in the central and eastern United States. American Journal of Tropical Medicine and Hygiene 72:622-630.
SANTAELLA, J., R. MCLEAN, J. S. HALL, J. S. GILL, R. A. BOWEN, H. H. HADOW, AND L. CLARK. 2005. West Nile virus serosurveillance in Iowa white-tailed deer (1999-2003). American Journal of Tropical Medicine and Hygiene 73:1038-1042.