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Cool nights suppress mosquitoes that can carry West Nile

While conditions started out ripe for

While conditions started out ripe for "a perfect storm" when it came to Suffolk County's mosquito population and West Nile presence, some cool overnight temperatures in August -- and the lack of hot, dry days -- means that storm hasn't developed. (Sept. 2, 2013) Credit: Science Source Images

While conditions started out ripe for "a perfect storm" when it came to Suffolk County's mosquito population and West Nile presence, some cool overnight temperatures in August -- and the lack of hot, dry days -- means that storm hasn't developed.

"It's not our worst and it's not our best" year, but it is "somewhere in between," said Scott Campbell, chief of the county health department's arthropod-borne disease laboratory. That's not to say that the virus is no longer a threat. "The risk still exists," he said, as humans have contracted the virus in September.

Still, as of Friday, the county was reporting 126 positive West Nile mosquito samples, with the virus widespread throughout the county, he said. Last year at that time, there were 201 positive samples; in 2011, 73; and 2010, 256, he said.

As for Nassau, there are 21 confirmed mosquito samples so far this year, with 75 reported last year as of Aug. 30, according to Mary Ellen Laurain, spokeswoman for the county health department. So far this year, the county has sprayed once with an eye to controlling adult mosquitoes, compared to 17 times last year, she said.

"A wet spring and hot, dry summer" mean large numbers of mosquitoes and "a lot of viral activity," Campbell said.

This year's rainy spring translated into "tremendous" numbers of mosquitoes in June and into July in Suffolk's traps -- thousands instead of the regular hundreds -- he said, leading to the likely West Nile carriers being culled out for testing and the rest frozen for future processing.

As numbers receded to normal, a seven-day heat wave struck in July, with 90-degree temperatures, and humidity making it feel like 100. Shortly after, the virus started appearing in mosquito samples, but a lucky break kicked in -- night temperatures in the 60s and 80-degree days helped slow down mosquito activity, he said. The "nighttime coolness," coupled with the possibility that people are wearing more covering clothing at night "is working to our advantage."

Still, that could change should warmer weather develop, he said. It's not until nighttime temperatures drop routinely into the 50s and leaves begin falling that mosquitoes start hibernating and dying off.

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