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Tuesday, September 20, 2016

West Nile Virus found in Nashua mosquitoes

By DON HIMSEL

Staff Writer

A state test has revealed West Nile Virus in a batch of mosquitoes that were collected in Nashua.

It is the only incident of the disease so far in the state this year. ...

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A state test has revealed West Nile Virus in a batch of mosquitoes that were collected in Nashua.

It is the only incident of the disease so far in the state this year.

West Nile and Eastern equine encephalitis are arboviruses that are transmitted from the bite of an infected mosquito.

The state Department of Health and Human Services said this is the first positive West Nile test result in the state this year, and there have been no positive tests for EEE so far.

Beth Daly, the chief of the bureau of infectious diseases for the New Hampshire DHHS, said the mosquitoes that tested positive were collected in Nashua on Sept. 13.

“We test from July 1 through Oct. 15,” Daly said. “That’s the time we are most likely to get a positive result.”

Daly said the virus needs time to develop in nature before it becomes problematic for humans.

Mosquitoes are collected in traps, placed into vials based on their species and transported to the state laboratory for testing. Daly said the state only tests certain species. They are ground up as a batch before testing.

“The mosquitoes out and about in May and June don’t typically carry these viruses,” she said. “It takes time to amplify in the reservoir population, which is birds, before mosquitoes pick it up and transmit it.

“Once there is a hard frost, all the mosquitoes die. They don’t overwinter, and there’s no longer any risk.”

Daly said the state tested about 1,500 mosquito batches in New Hampshire this year, mostly from the southeastern portion of the state.

“That’s historically where we’ve had activity,” she said, adding that this part of the state is more supportive of testing because it’s where there have been human cases of the diseases.

There have been no reported cases so far this year of a human or animal infection, according to the DHHS.

There is no state-run mosquito control program in New Hampshire. Each town or municipality dedicates funds to collect specimens and control mosquito populations. State testing is done at no charge.

Daly said the highest risk for infection is from late August to the fall frost, as the virus has gone through its “amplification process.”

State epidemiologist Dr. Benjamin Chan encouraged New Hampshire residents to “take precautions to prevent being bitten by mosquitoes as we head into the fall, the most risky time of year for mosquito-borne illnesses such as WNV and EEE.”

Don Himsel can be reached at 594-6590, dhimsel@nashuatelegraph.com or @Telegraph_DonH.