West Nile found in human-biting mosquitoes

NEW HAVEN » The risk of people contracting West Nile virus may be rising, as a mosquito species that is more likely to bite humans has been found to carry the disease, according to Philip Armstrong, medical entomologist at the Connecticut Agricultural Experiment Station.

As of last week, mosquitoes carrying the virus had been found in 20 towns, more than at this point in 2016, including six in Greater New Haven and seven in Fairfield County. But the West Nilecarrying mosquitoes have been found farther afield, in Hartford and New London counties, Armstrong said Thursday.

The most common species to carry West Nile is the northern house mosquito, Culex pipiens, which feeds mainly on birds, Armstrong said. However, what’s “really most alarming,” he said, is that “we’re also detecting the virus in human-biting mosquitoes.” That species is Culex salinarius, a common mosquito, “but what’s unusual is that it’s picking up the virus,” Armstrong said.

“This is the peak period of risk right now,” Armstrong said, although no human cases have been reported this year.

“The virus will amplify or will peak in the mosquito population usually before we have human cases,” he said. “There often are delays in diagnosis and reporting of these cases ... oftentimes weeks after the date of onset.”

There was just one human case of West Nile reported in 2016, compared with 21 in 2012, according to the state Department of Public Health. There have been 131 human cases of West Nile, including three fatalities, since 2000, according to Agricultural Experiment Station.

Armstrong said hot weather increases the mosquito population, “so with West Nile virus, typically when you have these prolonged heat waves ... the population will increase and biting will increase,”

Armstrong said.

“The bottom line is we are seeing a substantial increase in the risk just in the last week or two and hopefully this is the peak,” he said. However, “the risk for acquiring West Nile virus will still extend until the first hard frost.”

Dr. Richard Martinello, medical director for infection prevention at Yale New Haven Hospital, said, “Most people who get exposed to West Nile virus don’t have any symptoms at all. It may be 10 to 20 percent who get infected [who] may experience signs and symptoms.”

Those include headache, body ache, joint pain, fatigue, vomiting and diarrhea. “There’s a whole multitude of different infections that may present the same way,” including enterovirus, said Martinello, who is also associate professor of internal medicine and infectious diseases at the Yale School of Medicine. “Less than one percent ... can have a serious infection due to West Nile,” such as meningitis and encephalitis.

As of Tuesday, the Agricultural Experiment Station had tested 148,154 mosquitoes from 91 trapping sites throughout the state and had found 55 mosquitoes carrying West Nile virus. The towns where West Nile-carrying mosquitoes have been found are Branford, Bridgeport, Darien, Farmington, Glastonbury, Greenwich, Guilford, Middlefield, New Canaan, New Haven, North Branford, North Stonington, Orange, Plainfield, South Windsor, Stamford, Stratford, West Hartford, West Haven and Westport.

The mosquito-trapping program had also identified 21 mosquitoes with Jamestown Canyon virus in the towns of Canaan, East Haven, Meriden, Milford, New Britain, North Haven, North Stonington, Plainfield, Ridgefield, Shelton, Wethersfield and Willington.

“We pick it up every year,” Armstrong said of Jamestown Canyon virus. It’s not really a significant public health concern. There’s been one documented human case of James Canyon virus in the state of Connecticut “since the mosquito program began,” he said. The symptoms are mild.

There have been no reports of the more serious Eastern equine encephalitis virus found in mosquitoes this year, according to the Agricultural Experiment Station.

Man dies of babesiosis

A tick-borne disease caused by a parasite, babesiosis, was responsible for the death of Michael Yoder, 55, of New Milford on Aug. 8, according to The Associated Press.

Babesiosis symptoms are similar to the flu, although severe cases can cause anemia that leads to organ failure. There was one death each from the disease in 2015 and 2016, the AP reported.