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The first human case of West Nile virus for 2015 in York County — and the ninth in Pennsylvania — was reported on Tuesday.

Since Aug. 20, the Pennsylvania Department of Environmental Protection Vector Management has reported 67 new York County mosquito samples testing positive for West Nile virus for a total of 232 positives this year.

In the most recent sampling, the largest collection of mosquitoes testing positive for the virus — 18 of the 67 — came from York City, followed by Springettsbury Township with 11 positive samples, Manchester Township with nine and West Manchester Township with six.

It's not surprising that cities are producing higher numbers though, said Thomas Smith, West Nile virus program administrator for the York County Penn State Cooperative Extension.

In the city: Because the traps being laid out for sampling are aimed to prevent the transmission of the virus, they are more focused in areas that are more populated.

"The point of our program is try to keep ahead of the transmissions as best as possible," Smith said.

"Of course, there are going to be mosquitoes out in farms and areas like that.

"I mean we can set up traps in the middle of a cornfield somewhere, but that's not protecting anything but the corn really."

Smith said the sheer amount of "stuff" in city areas also draws in the mosquitoes.

Buildings, cars and other amenities that give off heat that are more prevalent in urban areas create a "heat island," Smith said.

A heat island refers to the fact that urban air and surface temperatures are higher than nearby rural areas.

It is the combination of slightly higher temperatures and any standing water there that draws the mosquitoes to city areas.

"The more people there are, the more stuff there is, the more places there could be standing water," Smith said.

Cutting down: While there has been spraying across the county and state to cut down on the populations, it's all for nothing if the mosquitoes can still find places to lay their eggs.

"Spraying only kills the adult mosquitoes," Smith said. "So if people don't clean up their properties within a week or so of spraying, the spraying won't do much."

It only takes a week for a mosquito egg to become an adult, Smith said. In two weeks, 10 mosquitoes could easily turn into a quarter of a million.

To help cut back on the population, "make sure anything at all that can collect water is turned upside down," Smith said.

Symptoms and prevention: The virus is transmitted through a cycle. An infected bird is bitten by a mosquito that then goes on to bite people.

If a person is bitten by an infected bug, the virus will manifest itself just as the flu, and like the flu, has no cure.

Those who are concerned about contracting the infection should look out for aching, fever and stomach pains among other flu-like symptoms, although people with stronger immune systems may not experience any symptoms at all, even if they are infected, Smith said.

On the other hand, those 50 and older or those who are sick are at risk for more severe symptoms.

Smith encouraged everyone to use bug repellent when outside, especially during the early evening hours.

"Electric fans are also good; mosquitoes don't like the wind," he said.

The threat of West Nile virus is most prevalent through September, though any type of tropical storm could extend that threat through October, Smith said.

— Reach Jessica Schladebeck at jschladebeck@yorkdispatch.com.

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