Mosquitoes in Waterford and Franklin are among the latest to test positive for West Nile virus during a summer that officials say has been a busy one for the pathogen.

West Nile virus has been found in mosquitoes in Connecticut every year since 1999. But this year mosquitoes are testing positive at higher rates and in more places than previous years.

"We're seeing a major expansion just this week," said Philip Armstrong, a medical entomologist at the Connecticut Agricultural Experiment Station, where mosquitoes from seven additional towns since last week have tested positive for West Nile.

One batch of mosquitoes collected on July 12 from a trap in the Franklin Wildlife Management Area and one collected July 18 on the Waterford/New London town line tested positive for the virus last week. Mosquitoes trapped in five Connecticut towns tested positive before last week, an indication for scientists that this summer could bring more West Nile virus to Connecticut than usual.

Staff at the Connecticut Agricultural Experiment Station collect mosquitoes from 91 traps in 72 municipalities — baited with carbon dioxide to replicate the air that humans and animals exhale or with water to attract breeding mosquitos — every 10 days, then send any traps with mosquitoes to the CAES lab in New Haven.

[naviga:h3]Mosquito testing - FY 2018[/naviga:h3]

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"Normally we don't have nearly this number ... at this point in the summer," Armstrong said. And, he said, the virus is showing up in parts of the state where it hasn't previously been seen, including places like Waterford.

"It's really expanded into a lot of new towns," he said. "That's an unusual spot — we don't normally see much activity there."

The infected mosquitoes, usually found in rural parts of the state, are appearing this summer in more urban areas. One of the species that transmits West Nile may be picking up the virus feeding on birds in rural areas and then making its way to other parts of the state, Armstrong said.

The human immune system usually can fight off the virus, and the chance of infection after a bite from an infected mosquito is less than 1 in 100. People who are infected usually have no symptoms or recover after a mild illness. In some people, particularly those older than 50, the virus can cause inflammation of the brain or meningitis, with symptoms ranging from a slight fever, headache, rash, swollen lymph nodes and nausea to the rapid onset of a severe headache, high fever, stiff neck, disorientation, muscle weakness and coma.

State health officials said 134 people have been diagnosed with West Nile in Connecticut since 2000, and three people have died in that time.

No humans or horses have been diagnosed with West Nile so far this year, Armstrong said. But people should prevent bites by wearing clothing that covers their skin and consider using insect repellent, especially around dusk and dawn, when mosquitoes are most active.

"The fact that we're seeing substantive buildup of the virus ... is a good indicator that now's the time to take protective action," Armstrong said.

The Ledge Light and Uncas health districts, which serve as the health departments for the municipalities in New London County, both issued notices of the positive West Nile tests and urged people to minimize the amount of time they spend outdoors at dusk and dawn, check their door and window screens and use mosquito netting if sleeping outdoors.

People should dispose of containers like pots or tires that can hold water where mosquitoes breed, clean clogged roof gutters, turn over things like small pools that might trap water when not in use and change the water in bird baths on a weekly basis.

Ledge Light Health District officials offered larvicidal briquettes that people can use to treat standing water on private property, preventing mosquitoes from developing into adults and reducing the potential for West Nile virus transmission.

People in the towns Ledge Light serves, East Lyme, Groton, Ledyard, New London, Waterford, Old Lyme, Lyme, Stonington and North Stonington, also can request treatment of standing water on their property by calling (860) 448-4882, ext. 1346.

m.shanahan@theday.com