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Rising mosquito numbers in Massachusetts bring West Nile virus concerns

Mosquito numbers are rising in some parts of Massachusetts, and with it comes the increasing concern about West Nile virus.

David Lawson of the Norfolk County Mosquito Control District said a wet spring and a dry start to the summer has played a large role in the insect's presence.

"If the rains stop, then the mosquito numbers will drop," Lawson said. "If the rains keep coming and it stays very wet, then we can expect the mosquito numbers to go up."

Entomologist Kaitlyn O'Donnell said the base for the mosquitoes is already there, and all they need is more rain.

"Their eggs are in the soil already, the ground," O'Donnell said. "As soon as that soil area is flooded with water, that's the key for them to hatch.

O'Donnell works with the Norfolk County Mosquito Control District, and has been monitoring the number of mosquitoes seen in the area with traps.

"It will catch mosquitoes that are looking for something to bite," O'Donnell said. "The one down the road, we'll usually get 3,000 in one night."

Overall mosquito numbers in Norfolk County are up over last year, and wet weather in the forecast threatens to drive those numbers higher.

The big concern that comes with the rain is when water collects in containers, tires and other places, where mosquitoes carrying the West Nile virus like to breed.

Many mosquito species carry the virus, but the main vector is the Culex mosquito, which saw a sharp spike in central Massachusetts last week.

West Nile-infected mosquitoes have also been found in Acton, Ayer and Northboro.

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Although the virus hit early in Norfolk County, it hasn't hit often. However, Lawson said that fact doesn't necessarily mean anything in July.

"We're a little early in the season," Lawson said. "West Nile is not at its height until we get into August and September, actually."