Saturday, August 24, 2002

West Nile Virus Alert

The National Wildlife Health Center issued this Wildlife Health Alert on August 22:

Wildlife Health Alert # 02- 01

To: Natural Resource/Conservation Managers
From: Acting Director, USGS National Wildlife Health Center
Title: West Nile Disease Continues to Move West - August 22, 2002

The West Nile virus (WNV) spread westward much faster than anticipated in 2002. It is believed that the fall and spring migration of millions of birds through affected states in 1999, 2000 and 2001, was the likely source of WNV for southern and western states. In 2002, West Nile virus is present to date in 39 states. Wild bird mortality is documented in 38 states and the District of Columbia and Wyoming has reported WNV in a horse (see map and website links). In addition, there are WNV positive birds reported in the four Canadian provinces of Saskatchewan, Manitoba, Ontario and Quebec.

The number of documented cases in humans and horses in 2002 has surpassed all previous years Human cases of WNV have been reported in 18 states and the District of Columbia with 14 deaths. The distribution of confirmed or probable human cases is LA (147, 8 deaths), MS (55, 2 deaths), TX (25), IL (9, 1 death), MO (5, 1 death), AL (3), OH (2), MI (2), WI (2), TN (1, 1 death), NY (1), AR (1), FL (1), MA (1), MD (1), KY (1, 1 death), IN (1), WA (1 contracted on travel to LA) and Washington DC (1). For comparison in 2001 there were 66 human cases with 10 deaths, in 2000 there were 21 human cases with 2 deaths, and in 1999 there were 62 human cases with 7 deaths. There are reports of 530 WNV confirmed or probable positive horses in 21 states. Western states have expressed concern that as WNV moves west it may infect wild horse populations.

With the rapid expansion of WNV into 11 new states this summer, including the western states of Colorado and Wyoming, WNV is expected to spread to the remaining 9 continental United States because of the high numbers of infected migratory birds and increased reports of infected mosquito species. Now that the virus is present in all of the Gulf coast states, there is concern that WNV will spread to the Caribbean and Central American countries.

Wild bird mortality continues to be the most sensitive method for early detection of WNV activity. Federal and state wildlife agencies and state and local health departments depend upon the testing of dead birds for their WNV surveillance. The American crow, fish crow, and blue jay appear to be the most susceptible species. As the virus has spread into the gulf and mid-western states, blue jays appear to be replacing crows as the most frequently reported species with the virus. Since 1999, scientists have detected the virus in 111 species of captive and free-ranging birds. The total mortality and impact on specific avian populations is unknown. Wildlife disease scientists are monitoring the possible increase of West Nile Virus infections in new species of birds, particularly other Corvidae species, as it moves west.

USGS is continuing to provide West Nile Virus surveillance support to state public health, wildlife, and federal agencies, including the military, which are collecting and testing wild birds to detect West Nile Virus activity in their areas. USGS mapping and wildlife disease scientists are continuing field research effort in collaboration with Centers for Disease Control and Prevention to investigate the role of migratory birds in disseminating the virus and in determining the pathways by which the virus is maintained and spread. Serum is being collected from migratory birds at multiple sites on US Fish and Wildlife Service Refuges, National Parks, and military facilities in the eastern half of the United States to test for WNV infection. This sampling will continue during the spring and fall migrations until the fall of 2003. The USGS is working with the Centers for Disease Control and Prevention again this year to map the geographic and temporal spread of WNV across United States. These maps are updated weekly.

To obtain further information and to report sickness or unusual bird mortality, contact Emi Saiko at or Kathy Converse at or call 608-270-2400 to reach the West Nile Coordinator at the National Wildlife Health Center.

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.


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