State officials also pledged to redouble a statewide effort to monitor for the virus. But they cautioned against overreaction, saying the discovery was expected and pointing out there have been no reported cases of the virus in humans in Massachusetts, or even in mosquitoes. The disease is fatal in only a small minority of people who contract it. The West Nile virus can cause encephalitis, a dangerous swelling of the brain which can be deadly. Most who contract it experience flu-like symptoms and never realize they have been exposed to the virus.
More severe infections can cause tremors, convulsions and sometimes death.
About 7 percent of those sick enough to be hospitalized for the virus die from it, according to the state public health department. In this area, we are used to protecting ourselves from mosquito bites because of Lyme disease. It wasn't clear whether the crow had picked up the disease outside of Massachusetts, or locally, said Dr. Ralph Timperi, assistant commissioner of the state's bureau of labs. Crows can fly up to 200 miles, and he confirmed this is the farthest the virus has been found in the U.S. from its epicenter in Queens, New York. Massachusetts health officials said they had already brought in 40 dead birds from around the state this year to test for the virus before one tested positive.