To: Natural Resource/Conservation Managers
From: Director, USGS National Wildlife Health Center (Robert McLean)
Title: Wild Birds Implicated in Rapid Spread of West Nile Virus

West Nile virus (WNV) infections are rapidly increasing in intensity and distribution in the United States as transmission to birds reaches its seasonal peak. The onset of the southward migration of millions of birds raises the concern that birds passing through affected states will likely move the WNV to southern states along the Gulf coast and possibly to countries to the south. Wild bird mortality due to WNV continues unabated with increased numbers and species of birds dying in 9 new States in 2001 (FL, GA, OH, AL, IN, LA, MI, WI, IL). An alarming but expected change was the detection of WNV for the first time in southern Georgia and northern Florida in June. This focus of infection was probably established during the 2000 fall bird migration and is now expanding in all directions, threatening people, horses, and birds. Four human cases have occurred in Florida and 1 human death has been reported in Georgia. This is in addition to 4 human cases in the New York City area and one case in New Jersey. In 2000 there were 21 human cases, with 2 deaths, and in 1999 there were 62 human cases with 7 deaths. Kentucky has only reported WNV in horses.

Wild bird mortality continues to be the most sensitive method for detecting WNV activity and state and local health departments depend upon the testing of dead birds for surveillance. The American crow, fish crow, and blue jay have been the most susceptible species so far and are experiencing high mortality. Other Corvidae (crows, ravens, jays, and magpies) may be equally susceptible and other bird species will likely be confirmed as the distribution of WNV expands. There is also a concern that the virus may pose a threat to bird species of concern such as the whooping crane, scrub jay, and wood stork in Florida. Since 1999 the virus has been detected in over 80 species of birds, including 60 free-ranging species from 20 states, the District of Columbia, and Ontario, Canada. As the virus spreads to more locations in Gulf coast states, and eventually the Caribbean and Central American countries, the threat of the virus spreading to additional Midwestern and Western states during subsequent spring migrations becomes greater.

The USGS National Wildlife Health Center is continuing to provide diagnostic support to local, state, and federal public health and wildlife agencies that are collecting and testing dead wild birds to detect WNV activity in their area. Active surveillance to detect the geographic expansion of the virus is ongoing in collaboration with US Department of Agriculture, US Fish and Wildlife Service, and state wildlife agencies that are sampling free-ranging wild birds in the eastern United States. This year USGS mapping and wildlife disease scientists began a field research effort in collaboration with Centers for Disease Control to investigate the role of migratory birds in disseminating the virus and in determining the pathways by which the virus is maintained and spread. Migratory birds were sampled at multiple sites in US Fish and Wildlife Service refuges, national parks, and military facilities from Florida to Massachusetts to test for WNV infection. This sampling will continue during the spring and fall for 3 years. Experimental research conducted by National Wildlife Health Center` demonstrated direct transmission of WNV between infected and uninfected crows under confined laboratory conditions and oral transmission from WNV-infected infant mice to crows. The efficacy of a commercial killed-virus WNV vaccine is currently being evaluated in crows.

This year the USGS Center for Integration of Natural Disaster Information (CINDI) is working with the Centers for Disease Control to map the geographic and temporal spread of WNV across United States. These maps are updated weekly and accessible at http://cindi.usgs.gov/hazard/event/west_nile/west_nile.html .

For further information and to report sick or dead crows or other unusual bird mortality contact Kathryn Converse at 608-270-1445, kathy_converse@usgs.gov , Kimberli Miller at 608-270-2448, kim_miller@usgs.gov, or Bob Dusek, at 608-270-2403, rdusek@usgs.gov

USGS WILDLIFE HEALTH ALERTS are distributed to natural resource/conservation agencies to provide and promote information exchange about significant wildlife health threats in their geographic region.