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State health officials have learned that six pelicans nesting at a waterfowl refuge in northeastern Montana have tested positive for West Nile virus. The discovery represents the first signs of the virus documented in the state this year.
Employees of the Medicine Lake National Wildlife Refuge reportedly discovered the dying birds July 19, 2004 on the refuge. They sent the bodies to the USGS National Wildlife Health Center in Madison, Wis., for diagnostic testing.
Scientists at the center completed tests early this week and shared results with officials at the Montana Department of Public Health and Human Services (DPHHS).
All six birds were nestlings, born this summer, according to Kathryn Converse, a wildlife disease specialist with the USGS facility. She said 2,000 pelicans at the refuge succumbed to the West Nile virus last year.
The identification of the virus in these birds means the West Nile season is officially open in Montana, said Jim Murphy, a disease surveillance specialist with DPHHS.
West Nile virus is carried primarily by birds but can be transmitted to humans by mosquitoes. It was first isolated in Africa in 1937. The first documented case in the United States occurred in New York in 1999, and the disease has since spread westward into nearly every state.
The first two documented human cases of the virus in Montana occurred in 2002, in Yellowstone and Rosebud counties. In 2003, the total number of cases in humans rose to 228, with four deaths reported. All were east of the Continental Divide. State health officials have expected the disease to hit western Montana this summer.
Although the virus can cause serious illness in humans, about 80 percent of people who are infected notice no symptoms and develop immunity. About 20 percent experience mild flu-like symptoms. About 1 in 150 people infected with West Nile develop severe illness, and about one in 1,000 cases is fatal. People over the age of 50 are at greatest risk of serious illness. Montana victims of the virus have ranged in age from 3 to 91. Fatalities have involved individuals aged 65 to 84.
In Montana, most cases of West Nile virus have occurred in August and September, when mosquitoes are active. Last year, 95 percent of reported cases occurred in those two months, according to Murphy.
Source: Montana Department of Public Health and Human Services