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
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.
History of WNV in the United States
WNV was first reported in the United States in New York State in the summer of 1999.
From 1999 to 2001 in the United States, 149 cases of illness and 18 deaths caused by WNV were reported in humans.
In 2002, State health departments reported more than 4100 cases and more than 280 deaths in humans to the electronic
surveillance system of the Centers for Disease Control and Prevention (CDC)*. In 2003 more than 9800 cases and 264
deaths in humans were reported.
CDC and NOISH