A horse from Derry is the first animal infected with Eastern equine encephalitis in New Hampshire this year.
The announcement was made yesterday by the state Department of Health and Human Services.
As a result of those findings, Derry’s risk level was raised to high and surrounding towns’ risk levels were raised to moderate.
That announcement followed news Wednesday that a mosquito batch collected in Sandown had tested positive for EEE and a batch collected in Hampstead tested positive for West Nile virus.
There has been a single human case of WNV in the state this year, an adult from Chesterfield who recovered from the illness.
As of yesterday, 13 mosquito batches have tested positive for EEE, 10 batches positive for WNV, according to Whitney Howe, the vector-borne disease surveillance coordinator for DHHS.
She and other public health officials warned residents not to let their guard down.
“It is a busy time of year for arboviruses,” Howe said. “August and September tend to be the busiest months.”
It will take a hard, killing frost to end the risk, something that could well be weeks away.
Last year was a very active year for WNV nationwide, she said, and New Hampshire was no exception. The state saw 41 mosquito batches test positive for the disease and had one human case.
For EEE, 2012 yielded nine mosquito batches testing positive and four animals.
“It’s the time of year that we do tend to find a lot of positives,” Howe said yesterday. “We’re waiting for a good hard killing frost. We want to make sure people are aware the risk of transmission for these illnesses is there until frost effectively ends mosquito season.”
Predicting the incidence of either illness is difficult, at best, she said.
“It’s very cyclical and difficult to predict,” Howe said. “In terms of hard numbers, it is about even, but there are still several more weeks of potential mosquito weather, so to speak.”
Towns are fighting back. Sandown officials have said they will spray again, as soon as weather allows.
Londonderry will spray town and school fields Saturday evening for the second time this year.
In Derry, town officials are consulting with Dragon Mosquito Control and will likely make a decision today, according to Garrett Simonsen, coordinator of the Greater Derry Public Health Network. Derry last sprayed on Aug. 30.
“These results highlight the fact that these illnesses affect not just mosquitoes, but animals and of course people too,” said Dr. José Montero, public health director at DHHS. “It is also an indication that mosquitoes do not respect borders, and as a result can infect animals and people in any corner of our state. This follows closely our identification of a person with West Nile virus in Chesterfield, so I want to reiterate the importance of protecting against mosquito bites, no matter where you live, until there is a killing frost statewide.”
The state will continue testing mosquito specimens through September, possibly into October, Howe said, depending on the weather.
Residents can call the state’s EEE/WNV information line at 1-866-273-6453 and find test results at www.dhhs.nh.gov.