State scientists this week began trapping and testing mosquitoes for viruses than can cause illnesses in people, including eastern equine encephalitis, or EEE, which all but bypassed Connecticut a year ago.

In 2020, mosquitoes infected with the potentially deadly disease were detected on single occasions in only two locations in the state: in Stonington and in the Windham County town of Hampton. No infections in people or horses were reported.

The previous year saw the worst EEE outbreak in state history, with four human cases occurring in southeastern Connecticut, three of which were fatal.

“I think we’re going to get off to a strong start in terms of mosquito collections,” Dr. Philip Armstrong, a medical entomologist with the Connecticut Agricultural Experiment Station, said Thursday. “There has been abundant rain followed by a heat wave. That sets up a perfect storm for the emergence of mosquitoes over the next couple of weeks. After that, it gets hard to predict, which is why we have to do the hard work of collecting them.”

The CAES coordinates the state Mosquito Management Program, which monitors mosquitoes for the presence of such viruses as EEE and West Nile virus, which can cause life-threatening neuroinvasive diseases, including encephalitis and meningitis.

Mosquitoes will be trapped at 108 sites in 87 municipalities across the state from now until October. The first test results will be available next week.

While mosquitoes carrying West Nile virus typically show up in late July and EEE-infected mosquitoes tend to be detected later in the summer, data gleaned from early collections helps scientists assess the season's risk of mosquito-borne diseases, Armstrong said. A lot depends on the weather going forward.

“If there’s a lot of rain, that will favor the mosquitoes that carry EEE, which is the disease of greatest concern in eastern Connecticut,” he said.

Last year’s drought was the biggest factor in limiting the disease.

“EEE never really became an issue last year, largely because the conditions were not conducive to it,” Armstrong said. “Things dried up in those swampy habitats where mosquitoes thrive. In Massachusetts, there were a number of human cases, but elsewhere, it was very quiet.”

West Nile virus was detected last year in 143 mosquito pools in 21 towns in Fairfield, Hartford and New Haven counties. Eight confirmed human cases were reported in Fairfield and New Haven counties.

Unlike West Nile virus, which appears every summer, EEE’s presence is difficult to predict from year to year.

“We can go several years where we see little or no activity in our state and then one year, it blows up as it did in 2019,” Armstrong said. “EEE often arrives in migratory birds from the South (which are then bitten by mosquitoes). If it’s introduced into the region at a time of high vectors (mosquitoes), the disease can explode.”

“Bv July, we’ll certainly know what to expect,” he said.

People are urged to protect themselves from mosquito bites by limiting outdoor activity around dusk and dawn, wearing long sleeves and pants and using insect repellent. Standing water, such as collects in clogged gutters and drains and garden pots, should be eliminated.

b.hallenbeck@theday.com