After a historically tough year in 2012, public health and mosquito control experts are uncertain about what to expect this summer.
What is certain is that after a rainy June and recent hot weather, the mosquitoes are out there in big numbers.
“We have a large population of summer flood water mosquitoes, and the marsh mosquitoes that come out every year in June and July,” said David Henley, superintendent for the East Middlesex and Suffolk County mosquito control projects, which serve 28 communities, including Boston. He said field technicians started collecting samples of mosquitoes from traps in the latter part of June.
“We’re seeing mosquito collections that are really large.”
In Massachusetts, the concern is about two mosquito-borne viruses that can potentially be fatal to humans: West Nile virus and Eastern equine encephalitis.
The trapping and testing is part of a system of surveillance done by mosquito control agencies around the state. Along with various forms of spraying or other treatments, the surveillance is a tool used to determine where the viruses are and whether infected mosquitoes are being found in increasing numbers. Along with treating catch basins or spraying, surveillance is a primary tool in managing the mosquito population, and therefore the illness risk.
The first — and so far only — West Nile virus finding of the season was found in a mosquito sample taken in Whitman on June 26. As they do every year, state and local public health officials are urging that people use precautions, particularly during the peak hours of mosquito activity, during dawn and dusk.
There were a record 33 human cases of West Nile virus in Massachusetts in 2012 and seven human cases of Eastern equine encephalitis, including two in Essex County that resulted in the deaths of people in Georgetown and Amesbury.
“It was the worst year for West Nile virus we’ve ever had, and the worst year for EEE since the 1950s, in terms of human cases,” said Dr. Catherine Brown, state public health veterinarian for the Department of Public Health. That department doesn’t officially track human deaths, she said, but at least three of the seven EEE cases resulted in deaths, as well as one West Nile Virus death.
There was also a dramatic spike in West Nile cases nationally, with 5,387 human West Nile cases reported in 2012. In 2011, the number of human cases was 712.
Part of his job is to prepare for the worst, acknowledged Jack Card Jr., director of the Northeast Massachusetts Mosquito Control and Wetlands Management District, which services 32 communities, primarily in Essex County.
“With what’s been happening, if it’s worse than last year it’s really going to be bad,” he said.
Experts have said that last year’s high number of cases had a lot to do with the hot temperatures, but predicting what will happen in this or any mosquito season can be difficult.
“For everything we know about West Nile and EEE, there is still a lot that we don’t know,” Brown said. “It makes it virtually impossible to predict accurately what a season is going to be like. That’s one of the reasons we rely so heavily on our mosquito surveillance data. By doing trapping and testing of mosquitoes, it helps us measure the season as it’s progressing and that’s what gives us our ability to assess risk.”
Brown advises people to stay aware of the surveillance data by checking in weekly with the Department of Public Health at www.mass.gov/dph/mosquito, which provides information, a risk map, and advice on how to protect yourself and your family.
State and local health departments recommend that people apply insect repellent with DEET while outdoors, be aware of mosquito activity particularly during peak hours of dawn and dusk, and wear light, long-sleeved shirts and pants, and white socks when outdoors. People are also advised to drain water from bird baths, gutters, and other potential breeding spots for mosquitoes, and to install or repair screens.
Brown noted that there are alternatives to using DEET.
“There are now multiple EPA-approved active ingredients that are found in different repellents, and so what I urge people to do is to pick one that works for you, because if you’re not willing to wear it, it’s not going to help you,” Brown said.
Amesbury and Salisbury Regional Health Department director Jack Morris, chairman of the Northeast Massachusetts Mosquito Control and Wetlands Management District, said the choices people make to protect themselves from mosquito-borne viruses should become part of the summer lifestyle, like applying sunscreen.
“We can assure people that West Nile virus and EEE are in the environment, and that people should use personal protection,” he said. “It’s like going out in the rain with an umbrella.”