Fears of West Nile virus rise with mosquito spike
Intermittent rains cited in early onset
A record number of potentially disease-carrying mosquitoes are expected across Massachusetts this year, and officials fear the spike in population could lead to more cases of West Nile virus.
"We're seeing about double [the mosquitoes] we saw last year," said Mary J.R. Gilchrist, director of the state's Bureau of Laboratory Sciences.
The Northern house mosquito has thrived in puddles of water left by the summer's intermittent rainstorms. Evidence of West Nile virus has emerged unusually early in the biting season, Gilchrist said.
The virus was first found this year in a pool of mosquitoes in Worcester on July 2, about a month earlier than last year. The virus has been found in four other tests since then. "It means more opportunity for the virus to build up," said Alfred DeMaria, state epidemiologist. "The early season amplifies the virus."
The most recent pool of diseased mosquitoes came from Needham, officials said yesterday during a news conference at Hinton State Laboratory in Jamaica Plain. The disease has been found twice in Brookline and once in Millbury this year.
The season's first infected birds, blue jays from Framingham and Newton, were found last week. The risk is not limited to where the disease has been found, DeMaria said.
Officials in Brookline have coordinated efforts to distribute information about the virus to households within a mile of the positive test locations, said Alan Balsam, the town's director of public health and human services. A nontoxic larvicide has been added to catch basins, he said, and residents can call a hot line if they find standing water.
No human cases of the virus have been reported in Massachusetts this year. Between 2000 and 2007, 59 people were identified as being infected, and six died. Officials said a second deadly virus carried by mosquitoes, Eastern equine encephalitis, has not been detected this year and may be declining.
The West Nile virus usually spreads to humans through a mosquito's bite. Illness ranges from a mild fever to more serious diseases like encephalitis or meningitis. Less than 1 percent of those infected develop serious symptoms.
Summer rainstorms are fueling the increased number of mosquitoes that are likely to carry the disease, officials said. Downpours fill flowerpots, bird baths, and clogged gutters, where mosquitoes lay their eggs. If the standing water is left undisturbed, a new batch of pests can emerge in as few as four days and live as long as six weeks.
"Potentially, there could be less of these mosquitoes with constant rain because it would clean out these areas," DeMaria said. But Bill Simpson, a spokesman for the National Weather Service, said the summer weather pattern is expected to continue.
Officials urged residents to take precautions. Outdoor events should not be scheduled between dusk and dawn. Repellents with DEET, permethrin, picaridin, or oil of lemon eucalyptus should be used if the weather is too hot to wear long pants or long-sleeved shirts. And homeowners should patch holes in window screens, clean gutters, and regularly clear standing water.
Christopher Baxter can be reached at cbaxter@globe.com.
