A first crow that tested positive for the virus was found at Greenbrier State Park last week, MacRae said.
Elsewhere in Washington County, a Boonsboro horse was being treated for suspected West Nile virus. A check Monday afternoon revealed the horse stabled at Homeward Bound Horse Rescue on San Mar Road was responding well to treatment.
In nearby Frederick County, Md., the health department has confirmed five cases of the disease in crows.
There have been no reports of positive testing in Berkeley, Jefferson or Morgan counties in West Virginia, according to a state Department of Health and Human Resources Web site.
The affected bird found in Franklin County, Pa., was the first this year, Richard McGarvey, of the Pennsylvania Department of Health, said from his office in Harrisburg, Pa.
It marks the third consecutive year a bird has tested positive for the virus in Franklin County, McGarvey said.
Officials didn't know where in the Greencastle area the crow was found or by whom.
Dave Stoner, a conservation technician with the Franklin County Conservation District, believed a resident might have left it at the dead bird drop-off center at the local health department office at 518 Cleveland Ave., in Chambersburg, Pa.
Residents who find dead birds are encouraged to contact the state health department, McGarvey said. Birds that have been dead for 24 hours or more are not suitable for testing, he said.
Symptoms of West Nile virus are usually mild in humans, but the most severe cases can be fatal, according to the U.S. Centers for Disease Control and Prevention's Division of Vector-Borne Infectious Diseases.
West Nile virus was first detected in the U.S. in 1999 and is primarily a concern for the elderly or for people with weakened immune systems.
Common symptoms are neck stiffness, headache, fever, seizures and disorientation.
There is no West Nile vaccine available for humans. There is one for horses.
Bird species most susceptible to the virus include crows, blue jays, hawks and owls. "It's especially fatal to crows, although no one seems to know why," McGarvey said. "Chickens get it, too, but it never bothers them."
Smaller species, including starlings, have been affected by the virus, he said.
Stoner said conservation district employees have been monitoring Franklin County looking for mosquitoes that carry the West Nile virus.
Live adult mosquitoes are captured at night in special lighted traps and sent to a state Department of Environmental Protection laboratory for testing, he said. District workers also trap mosquito larvae in stagnant ponds for testing.
So far, none of the mosquitoes trapped in Franklin County has tested positive, he said.
McGarvey said many more birds, mostly crows, have been found with the virus in the Philadelphia area than anywhere else in Pennsylvania.
"There's a higher awareness of the disease there," he said. "More people are collecting more birds."
Last year, 153 birds in Bucks County, near Philadelphia, tested positive," he said. "There have been 50 so far this year."
The Centers for Disease Control and Prevention reported Saturday there have been at least 251 human cases of the disease this year. Eleven people nationwide have died from the disease.
States most affected are Louisiana, Mississippi and Texas.
Maryland residents who have found dead birds have been calling a statewide number, 1-866-866-CROW (2769), and the health department in that county goes out and picks up the birds for testing, MacRae said.
The number for the health department in Chambersburg is 717-263-4143.