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NMSU Scientists Eye Bird Source for West Nile Virus

LAS CRUCES - New Mexico State University researchers are jump-starting research to better understand birds' role in the rapid spread of West Nile virus across the state.

Don Caccamise, head of New Mexico State University's fisheries and wildlife sciences department, and graduate student Holly Vuong set up a mist net used to trap birds as part of new research project to find New Mexico's source of West Nile virus. The disease is passed to humans by mosquitoes that have fed on infected birds. (08/29/2003) (NMSU Agricultural Communications Photo by J. Victor Espinoza)

Scientists are trapping mosquitoes and birds in Dona Ana County, and they believe they're on track to manage West Nile virus and its potentially life-threatening complications as it develops a permanent foothold here in New Mexico.

The virus, passed to humans by mosquitoes that have fed on infected birds, can cause flu-like symptoms in humans and potentially fatal swelling of the brain. The disease is named after Uganda's West Nile region, where the virus was first discovered in 1937.

"Our goal is to find the source of the virus in New Mexico," said Don Caccamise, an avian ecologist and head of NMSU's fisheries and wildlife sciences department. There are three possibilities: The disease is recycled annually through overwintering adult mosquitoes, resident birds retain the virus over the winter months or migratory birds bring West Nile to the state in the spring.

"We just don't know, but we've got some good ideas," Caccamise said. "Last winter West Nile was found deep in southern Mexico for the first time. Mexico had no West Nile, so it's likely that virus was brought in by our birds when they migrated south for the winter."

With funding from the New Mexico Department of Health, NMSU researchers are genetically testing birds and mosquitoes and looking for the virus or antibodies against it in the birds' blood. "A number of habitats are being studied, from agricultural fields to urban areas," Caccamise said. "The project will initially center on southern New Mexico, but as the project develops we'll expand to other areas."

The scientists are searching for so-called bird reservoirs for West Nile, Caccamise said. Each bird community is a bit different, as is the timing of their arrival in the region. The fact is that a lot of the birds that get the virus are not capable of infecting mosquitoes, he said.

"They are dead-end hosts," Caccamise said. "These birds get sick and may die, but they don't develop enough of the virus to become transmission sources. We need to know which ones are involved in the transmission cycle."

Moreover, not all types of mosquitoes carry the virus, said Carol Sutherland, an entomologist with NMSU's Cooperative Extension Service. Among those that do, some make better carriers than others, she said.

Researchers will be closely examining which mosquitoes are implicated in New Mexico's spread of West Nile. "No matter where you go, the mosquito community and its relationship with the virus are likely to be different," said Ron Byford, one of the project leaders and head of NMSU's Extension Plant Science Department. "What we need to do in New Mexico is find which mosquito species are involved in transmitting the virus, where they live and what the seasonality of their disease cycle is," he said.

With specific bird and mosquito information in hand, state officials can begin developing a targeted, cost-efficient plan for controlling infected mosquitoes, Byford said.

According to the federal Centers for Disease Control and Prevention, less than 1 percent of people infected become severely ill. Victims may develop flu-like symptoms, including headaches, fever or muscle aches for a few days, but generally get better.

Older Americans appear to be at greatest risk of developing West Nile fever or its most severe complication, a potentially deadly swelling of the brain called encephalitis. New Mexico now has a total of 43 confirmed cases of human West Nile infections. Three people have died as a result of the mosquito-borne virus, an 88-year-old Rio Rancho woman, a 78-year-old Roswell man and a 76-year-old San Miguel County woman.

In addition, there have been more than 224 cases reported in horses in 28 New Mexico counties, said Paul Ettestad, a veterinarian with the New Mexico Department of Health's Office of Epidemiology.

West Nile virus was never seen in the Western Hemisphere and was virtually unknown to American health officials before a 1999 outbreak in New York. Now, 1,602 cases are confirmed nationwide, nearly half occurring in Colorado. So far, federal officials report 28 U.S. deaths.