Environment Public health vet offers mosquito outlook

BOSTON - The state's public health veterinarian delivered a mixed outlook last week for mosquito-borne illnesses this summer in Massachusetts.

Dr. Catherine Brown, who also serves as the Department of Public Health's deputy epidemiologist, told the Public Health Council that recent weather conditions will likely have divergent effects on the different mosquito populations that carry West Nile virus and eastern equine encephalitis (EEE).

Projecting that warmer days and episodic rainstorms will lead to "a really good year" for the mosquitoes that can carry West Nile virus, Brown said she anticipated a "relatively small population" of mosquitoes that can carry EEE.

Mosquitoes that spread EEE lay their eggs in the types of swamps most common in southeastern Massachusetts, and last year's drought left little water in those areas, Brown said.

"That's good news," she said. "It means we're starting with a very low population of the mosquito that kind of starts that whole amplification cycle. Because we had so much rain this spring, as long as we continue to see rain throughout the season, we should consider this year probably to be a rebuilding year-if you'll forgive the sports analogy-for EEE, and then we'll start to see the population tick back up after those drought years, and it may emerge as a more significant issue next year."

Brown said West Nile is more prevalent in urban areas, where stagnant water collects in small pools in items like gutters, birdfeeders and children's toys left outside.

The state public health laboratory on June 29 confirmed the presence of West Nile in a mosquito sample collected from the town of Richmond in Berkshire County, marking the first time this year the virus was detected. Brown said West Nile has now been found in three samples, each from different areas.

"It's an average time for us to have those findings, so it's not unexpectedly early, but it is interesting that they've occurred from three different parts of the state, indicating at least at this point we probably have some level of risk for West Nile virus, a low-level risk, widespread," she said.

Brown said the best way to avoid mosquito-borne illnesses is by avoiding mosquito bites by applying insect repellent to clothes and exposed skin and wearing long pants and sleeves, particularly around dawn and dusk when mosquitoes are most active.

Surveillance efforts have identified 53 species of mosquito in Massachusetts, according to Brown, who highlighted a non-native, tropical species first identified here in 2009. She said the species, aedes albopictus, has been in the southern United States for decades and is moving north as it gains the genetic ability to survive colder temperatures.

Aedes albopictus is most commonly associated with diseases that do not occur here, like dengue, Brown said, and is not the "primary vector" of those diseases. She said it does not seem to contribute to West Nile or EEE activity.

Brown said public health officials consider the presence of the mosquito "noteworthy" and in need of monitoring.

"What we need to all hope for is a really, really cold winter with no snow, and that will really help us with this mosquito," Brown said.