One person has died in New Hampshire after contracting the mosquito-borne virus Eastern equine encephalitis, and two others in the Northeast have been infected this summer with the rare disease.

Health officials in the Northeast said that there was an elevated risk for the virus and urged residents to take precautions between dusk and dawn, when mosquitoes are most active.

What is E.E.E.?

The disease, like West Nile virus, is transmitted by mosquitoes, but E.E.E. has a higher death rate and is more rare. It is not contagious from person to person.

There is no treatment for the disease, and about 30 percent of people who get it die, according to the Centers for Disease Control and Prevention. Many people who survive the illness have continuing neurological problems.

How common is it?

There are only a few cases of the disease each year in the United States, according to the C.D.C., and most of the cases are in eastern or Gulf Coast states.

The states that have reported cases this year said it was the first time that they had found the virus in residents in years.