Mosquitoes infected with the West Nile virus have been found in 17 towns in the state this season, the Connecticut Agricultural Experiment Station, or CAES, reported Thursday.

The list, which a month ago included only Darien, Fairfield, New Haven and Stamford, now also includes Ledyard in southeastern Connecticut as well as Branford, Bridgeport, Greenwich, Hartford, Milford, New Canaan, Norwalk, Stratford, Wallingford, West Haven, Westport, and Woodstock.

CAES experts expect the disease to continue spreading geographically among mosquitoes as the summer continues, increasingly imperiling residents, who can catch the disease if bitten by an infected mosquito. No human cases of West Nile virus have been detected this year in Connecticut. Since 2000, the state has had 173 human cases, four of which were fatal.

Two human cases of the disease have been reported in New York City, where the number of infected mosquitoes has soared to record levels, it was announced this week.

“We are seeing a sharp rise in the numbers of mosquitoes carrying West Nile virus, especially in coastal Fairfield and New Haven counties and in the metropolitan Hartford area,” said Dr. Philip Armstrong, a medical entomologist who directs the CAES mosquito-monitoring program. “We anticipate further geographic spread and build-up of West Nile virus in mosquitoes, with increased risk of human infection, from now through September.”

Armstrong, reached in his office, had some good news about another mosquito-borne disease the CAES monitors every year. He said eastern equine encephalitis, or EEE, has not been detected among mosquitoes collected at any of the agency’s 108 trapping stations in 88 municipalities.

The CAES increased its testing in eastern Connecticut in the wake of a deadly EEE outbreak in 2019. Four human cases resulting in three fatalities occurred in southeastern Connecticut that year.

“We’re testing for the EEE virus but we’re not finding it,” Armstrong said.

EEE outbreaks tend to be preceded by sustained increases in the population of a particular species of mosquito (Culiseta melanura) that “amplifies” the virus in bird populations, according to Armstrong. Mosquitoes transmit the disease from birds to horses and people.

“Our trap collections for Culiseta melanura mosquitoes are well below our long-term average,” Armstrong said. “It has been very dry this summer and this species depends on abundant rainfall to ensure adequate water levels in its primary habitat ― forested swamps ― for larval development.”

He said the CAES will continue to monitor the mosquito population until the first hard frost of the year, which usually occurs in October.

Though less lethal than EEE, the West Nile virus still poses a serious threat to people. About 20% of those infected with the disease develop fever and a rash that usually resolves over several days or a week; one in 100 people who contract the disease develop encephalitis or meningitis and require hospitalization, according to Armstrong. The disease can be fatal.

EEE, which is more rare than West Nile, has a 30% mortality rate among people, and those who survive it can experience serious long-term effects.

In a statement, Dr. Jason White, the CAES director, urged residents to take steps to prevent mosquito bites. He said they should:

• Minimize time spent outdoors between dusk and dawn when mosquitoes are most active.

• Consider the use of mosquito repellents containing an EPA-registered active ingredient, including DEET, Picaridin, IR3535, oil of lemon eucalyptus, para-methane-diol, (PMD), or 2-Undecanone, when it is necessary to be outdoors.

• Wear shoes, socks, long pants, and a long-sleeve shirt when outdoors for long periods of time, or when mosquitoes are more active. Clothing should be light-colored and loose-fitting and made of tightly woven materials that keep mosquitoes away from the skin.

• Be sure door and window screens are tight-fitting and in good repair.

• Use mosquito netting when sleeping outdoors or in an unscreened structure and to protect infants when outdoors.

b.hallenbeck@theday.com