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.