Heavy Rain Breeds Mosquitoes, Increased Risk of Disease

June 27, 2013

We all know there's no better place to be in the summer than New England. From the coast to your backyard, there's plenty to do and places to see.

But this month, we've also had to deal with three times more rain than usual. And all this rain is a breeding ground for mosquitoes, and perhaps dangerous diseases.

"There’s a lot of mosquitos out here right now," said Dave Lawson, who directs the Norfolk County Mosquito Control District. "You can see all these in the grass here." 

Mosquito larvae live in stagnant water.
Caption
Photo Credit: Ibby Caputo / WGBH

We’re at University Road in Canton, at the edge of the Neponset River Flood Plain.

"You can clearly see here that the water is very high," Lawson said. "This is not normal. We’re only probably 20 feet from the road, and the water is right there."

That means a lot of mosquitoes.

Before a mosquito bites you, it undergoes a metamorphosis.

Just as a butterfly starts off as a caterpillar, a mosquito starts off as a larva.

"There’s a mosquito larvae right there, see that moving?" Lawson said, pointing to what looks like a tiny worm, wiggling around. "See, it’s sticking at the surface of the water. People sometimes refer to them as wigglers because you see them sort of wiggling through the water."

Lawson says by the weekend, these wigglers will have turned into mosquitoes, leading to lots of phone calls. The Norfolk County Mosquito Control District is already getting a lot of phone calls.

Residents from Norfolk, Canton, Quincy and other towns that pay for this state service can request a truck to spray their neighborhood in an attempt to kill off the mosquitoes. Spraying not only helps keep mosquitoes from ruining your summer barbecue party, but it also limits the spread of disease.

Last year was a record-breaker for mosquito-borne illness in Massachusetts. There were 33 cases of West Nile Virus, which causes flu-like symptoms, and seven cases of Eastern Equine Encephalitis, or Triple E, which causes neurological damage and death.

"As we start to get into August and September that’s when the risk becomes higher," said Steven Rich, a professor of microbiology at the University of Massachusetts, and an expert in ticks and mosquitoes. "So there are hundreds of different mosquito species, and not all of them feed on all of the different species of mammals and birds that are associated with the virus transmission."

Some mosquitoes prefer birds, others prefer mammals.

"The ones that are a concern are the ones that like to feed on birds and mammals, because those are the ones that are called bridge vectors that carry the viruses from a bird into a mammal population," Rich said.

West Nile and Triple E are bird viruses. A mosquito that feeds on an infected bird becomes a carrier of the virus. That mosquito can then feed on other birds, passing the virus onto them, which in turn infects more mosquitoes. The more birds and mosquitoes that have the virus, the more likely a bridge vector mosquito will pass the disease onto a human.

It’s Lawson’s mission to help stop the spread of disease.

"Whoops, I got one on my head," he said, smacking his head and laughing.

His arsenal includes a helicopter that spreads an insecticide called BTI.

"We put this in the water," he said. "This is mostly actually ground up corncob, which is the base, and then the bacillus bacteria is actually sort of glued on the surface."

Lawson picks up a handful of the BTI. They look like Grape Nuts. He lets them run through his fingers. BTI is toxic to mosquito and black fly larvae. He throws some in the water.

But even the widespread use of BTI cannot kill all the larvae. That’s why the Massachusetts Department of Public Health monitors mosquito populations and tests them for disease.

Along a footpath near the water, an adult mosquito trap is tucked in among trees. There’s what looks like a small car battery on the ground, wired to a light on a net, and a tank.

"So this is a tank – carbon dioxide, compressed carbon dioxide, and we have it coming out through this little nozzle right here, and so the mosquitoes are attracted to the CO2, they’re attracted to the light, they come up here and then the fan sucks them down into here, and so you can sort of see them on the side of the netting there," Lawson said.

Lawson lifts up the trap so I can see where the mosquitoes enter. There’s a lot. It looks like hundreds.

"Looking for blood," Lawson said.


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