The state Mosquito Management Program said Thursday mosquitoes in six towns — including Waterford — have tested positive for West Nile virus in the latest round of testing.

The Connecticut Agricultural Experiment Station trapped the positive mosquitoes in Darien, Guilford, New Haven, Stamford, West Haven and Waterford from July 20-29, according to a news release.

The state Department of Public Health announced on July 31 that mosquitoes trapped in Waterford on July 20 tested positive for the virus.

It was the first occurrence of mosquitoes testing positive for West Nile virus in the state so far this year.

“The number of infected mosquitoes and the number of affected towns is increasing,” Dr. Philip Armstrong, medical entomologist at the agricultural station, said in a prepared statement. He expects to see more buildup of the virus in mosquitoes with increased risk of human infection during the rest of the summer and into early fall.

August and September are historically the months when risk of West Nile virus infection is the greatest, said Dr. Theodore Andreadis, of the Center for Vector Biology and Zoonotic Diseases at the agricultural station.

“We encourage everyone to take steps to prevent mosquito bites, such as using insect repellent and covering bare skin, especially during dusk and dawn when biting mosquitoes are most active,” he said in a statement.

So far this season, there have been no reports of people or horses with illnesses associated with West Nile virus, the news release said. Last year, six people developed West Nile virus-associated illnesses, none of which was fatal, the release said.

Since 2000, the state has confirmed 120 cases of people with West Nile virus-associated illnesses, including three deaths, the release said.

d.straszheim@theday.com

Twitter: @DStraszheim