Sally Paulson, an associate professor of entomology, said the find from samples taken last year and recently analyzed was surprising because no human cases of the disease had been reported in the counties before.

"It surprised me to get so many positives from so few samples from a place I wouldn't have expected any," Paulson said.

The counties in which the positive samples were collected for the first time were Montgomery, Giles, Pulaski, and Floyd. The disease had previously been found in the counties of Wise, Dickenson, Buchanan, and Tazewell. About 15 human cases of La Crosse encephalitis have been reported in Virginians in the past 10 years.

The positive results were returned from approximately 135 "pools," samples containing a number of mosquitoes captured at individual locations. Because the laboratory report only reports a positive result from a pool, Paulson said it is impossible to say exactly how many individual mosquitoes were infected.

"We had seven positives reported, and our collecting methods did not target the species that carry La Crosse virus," she said. Paulson and her graduate students collected the samples as part of a project to check for West Nile virus. Different mosquito species are implicated in the two diseases.

The mosquitoes that spread La Crosse virus are members of the Aedes and Ochlerotatus genera. The Eastern Tree Hole Mosquito is the primary vector for the disease, though the Asian Tiger Mosquito has also been implicated in its spread. Both live in woodland habitats but can be abundant in urban and suburban areas.

According to a fact sheet on the disease from the Centers for Disease Control, about 70 people are infected with La Crosse encephalitis nationwide each year, though the agency considers the num
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Contact: Stewart MacInnis
macinnis@vt.edu
540-231-5863
Virginia Tech
30-May-2003