A batch of mosquitoes collected in Manchester on Aug. 30 has tested positive for West Nile Virus, the city health department reported.

It’s the first batch to test positive in the city this year.

“This is the time of the season that we can expect West Nile Virus to be identified in New Hampshire,” Manchester Public Health Director Anna Thomas said in a news release on Thursday.

“It is important for residents and visitors to take steps to prevent mosquito bites, as WNV and other arboviruses can be transmitted to humans from the bite of an infected mosquito.”

She said until there is a mosquito-killing frost, the risk of infection by mosquito-borne viruses may increase and people should use mosquito repellant and avoid being outdoors at dawn and dusk.

First identified in New Hampshire in 2000, West Nile virus is one of three “arboviruses” transmitted by mosquitos here. The others are Eastern Equine Encephalitis (EEE) and Jamestown Canyon virus (JCV).

Symptoms of West Nile infection usually appear within a week after a bite, causing flu-like illness including fever, muscle aches, headaches and fatigue.

Many people develop no symptoms or very mild symptoms, but a very small percentage of those infected can go on to develop more serious central nervous system disease, including meningitis or encephalitis, according to the state Department of Health and Human Services.