BOSTON (AP) – An 81-year-old Missouri man has been diagnosed as the first human case of West Nile virus in Massachusetts this year.

Department of Public Health officials say he was probably not exposed in Massachusetts. He traveled to Martha’s Vineyard Aug. 5 and became ill Aug. 11.

Missouri has reported five human cases of West Nile virus this year. Massachusetts Department of Public Health spokeswoman Donna Rheaume said mosquito pools in Martha’s Vineyard have not tested positive for the virus.

“Martha’s Vineyard, the Cape and the Islands are not a traditional place where we’ve confirmed cases of West Nile,” Rheaume said. “We think it’s unlikely this person got the virus in Massachusetts, but cannot rule it out because of the timing of the trip.”

The man is recovering at a Boston hospital, Rheaume said. The state may increase testing of mosquito pools in Martha’s Vineyard, she said.

West Nile virus has an incubation period of three to 15 days, making it difficult to tell when he may have contracted it, Rheaume said.

A bird in Marlborough tested positive for the disease last month. Three human cases were reported last year in Massachusetts but none were fatal.

Symptoms of the insect-borne virus range from mild flu-like illness to inflammation of the brain, coma and even death.

AP-ES-08-23-07 1814EDT