A batch of mosquitoes collected in Salem is the first in New Hampshire to test positive for West Nile virus this year.
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The Department of Health and Human Services says it is working with town officials to notify residents.
Dr. Benjamin Chan, state epidemiologist, said the risk of infection is present throughout the state, and that it's important to take steps to prevent mosquito bites until there is a killing frost.
West Nile virus was first identified in New Hampshire in August of 2000.
Symptoms include flu-like illness including fever, muscle aches, headaches and fatigue.