West Nile Virus and Public Health

Wildlife disease scientists at the National Wildlife Health Center (NWHC), the CDC, and other federal and state public health and wildlife agencies in the national WNV surveillance program are monitoring birds for the presence of the virus. In addition, the NWHC is working with federal and state wildlife officials in investigating local and regional wildlife die-offs potentially due to WNV. These and experimental studies in the Center’s biosafety level-3 (BSL-3) laboratories have allowed scientists to explore, and subsequently understand, not only the public health importance of the virus’ arrival in the Western Hemisphere, but also its potential effect in wild bird populations.

USGS geographers are contributing to the national WNV surveillance effort by mapping WNV cases as they are reported to the CDC. This has allowed the CDC and the general public to monitor the virus’ geographic movement as well as trends and clusters during each season across the continental U.S. In addition, USGS and the CDC are investigating the ecology of potential WNV vectors and reservoirs in Louisiana . Using remote sensing and geographic information systems to map habitats and environmental factors USGS and CDC are seeking to develop better models for understanding the associations between reservoir hosts, mosquitoes, environmental and climate conditions, and the virus. When West Nile virus was first detected in New York, local governments began increasing insecticide use. USGS quickly recognized the need to develop highly sensitive tests and analyses to monitor these insecticides. This information is vital to land managers and vector-control agencies to ensure that insecticides are safe and effective. On Long Island , USGS is testing area waters for several insecticides, including resmithrin, sumithrin, malathion, and methoprene. USGS also monitors for a byproduct of methoprene and for the chemical piperonyl butoxide, which is used to enhance the effectiveness of some of the insecticides. These data help officials manage insecticide application and helps answer broader questions needed for environmental risk assessment of how these insecticides move through our environment.

USGS is also studying the role migrating birds play in disseminating West Nile virus. Investigators have captured and sampled more than 12,000 birds over the past 3 years at 8 different study locations along the east coast and 5 study locations along the Mississippi River . Based on the detection of WNV specific antibodies in these birds, scientists are seeing an increasing number of birds that have been exposed to and survived infection with WNV. Scientists have also detected WNV viremias in 19 birds, primarily along the east coast in fall of 2003. While this represents very few of the birds sampled, all these birds were sampled at a critical time of migration when birds were moving southward almost daily. If these birds remained healthy and if they migrated southward shortly after sampling, they could have transported WNV along the migration corridor but more analysis is needed to understand the implications of these findings.