Throughout the warmer months, Jeffrey Carroll and a team of field technicians set traps to collect pregnant mosquitoes around the Lehigh Valley.
The captured mosquitoes are sent to Harrisburg, where they’re liquefied and then tested for West Nile Virus, an infection that first came to Pennsylvania in 2000 and typically comes with flu-like symptoms, but in rare cases can result in death.
It’s an especially important job this year because the Department of Environmental Protection is reporting the highest levels of West Nile in the mosquito population since the virus first appeared in the state.
Carroll, Penn State Extension’s mosquito borne disease control coordinator for Lehigh and Northampton counties, has captured numerous mosquitoes this summer that tested positive across the Lehigh Valley.
State experts count West Nile-carrying mosquitoes in “pools,” in which mosquitoes collected at any site are tested in groups of 100 or fewer. Researchers have tallied a record 2,143 pools of West Nile-positive mosquitoes statewide. The previous high was in 2012, when they counted 1,363 virus-positive pools. Philadelphia, Lancaster County, York County and Chester County are driving the trend, said Matt Helwig, the West Nile Program specialist at the DEP.
“With record levels of West Nile virus activity in mosquitoes already found, we are at increased risk of disease from a bite of a mosquito. It is imperative that Pennsylvania residents take common-sense precautions to protect themselves from mosquitoes,” said DEP Secretary Patrick McDonnell in a news release. “There has been one human case already this year. Our goal is for that to be the only one. By eliminating places for mosquitoes to lay eggs, using insect repellent and other protective measures, and targeted use of pesticides, we can all make sure Pennsylvanians are protected.”
Lehigh County, where there have been 50 positive pools, and Northampton County, with 26 pools, are the 13th- and 23rd-highest counties respectively, Helwig said. The virus was found in mosquitoes in in 51 of 67 Pennsylvania counties.
Carroll said West Nile is elevated in the Lehigh Valley this year, but no records have been broken.
Carroll and Helwig recommend people eliminate any artificial containers with standing water on their property, like buckets, wheelbarrows or toys. The pool of water that collects in a single upturned bottle cap can incubate hundreds of eggs.
Use of commonly sold insect repellants, like those using DEET, Picaridin, or other EPA-registered repellants, can also cut down on mosquito bites, and possible exposure to the virus. Long pants and sleeves are also an important way to cut down on possible exposure to mosquitoes.
Helwig and Carroll said the wet, hot weather is driving the increase in West Nile. The rain and flooding eventually leave standing pools of water, creating perfect mosquito breeding grounds.
Mosquito breeding and biting also increases with hot weather, Helwig said.
He explained mosquitoes spread the disease among the bird population. Those known to bite both birds and humans act as a vector to spread the virus between the species.
Female mosquitoes eat one “blood meal” and then lay 300 eggs, a process that they can go through up to four times.
“The ones that pass [West Nile] on are the ones who have fed on a blood meal before, laid eggs, are now infected with the disease, and would take a second blood meal to start that process again,” Helwig said.
West Nile causes mild flu-like symptoms, but it can lead to a more serious condition that includes swelling of the brain, muscle convulsions, coma, paralysis and death, according to the DEP. There have been 33 fatal cases of West Nile in Pennsylvania since the DEP first started monitoring the virus in 2000.
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