CORVALLIS, Ore. - Veterinary diagnosticians at Oregon State University have confirmed that a dead crow found in the eastern Oregon town of Vale near the Idaho border has tested positive for West Nile Virus.

The virus is transmitted by mosquitoes, and birds are prone to infection. Humans and horses can become infected as well, according to Dr. Jerry Heidel, director of the Veterinary Diagnostic Lab in OSU's College of Veterinary Medicine, which tested the crow.

Birds - especially crows and jays - often provide the first visible signs that West Nile Virus has arrived in a region, Heidel said. The Centers for Disease Control and Prevention lists more than 100 species of birds that have been found to be infected by the virus.

"There is no doubt about the diagnosis," Heidel said. "We used the extremely sensitive and specific polymerase chain reaction, or PCR, test on this bird and it is definitely West Nile Virus. Oregon has been one of the last states without West Nile Virus until now."

The crow was discovered through the statewide surveillance program initiated by Dr. Emilio DeBess, Oregon Public Health Veterinarian.

"As part of the program, counties submit suspect birds for diagnostic testing," Heidel said. "If you find a dead crow, you have to have it in the back of your mind that this could be a case of West Nile Virus, especially during mosquito season.

"However, other things can kill birds and we really don't know if it is West Nile until we perform the PCR assays," he added.

The PCR assay amplifies the genetic material of the West Nile Virus, allowing the veterinary diagnostic specialists to more easily identify the virus in tissue samples taken from the brain of the suspect animal.

Heidel said horses also are very susceptible to infection from the disease and recommends that horse owners consult with their veterinarian regarding vaccination of their animals against this disease.