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Traps are returning high numbers of mosquitoes in York County — many of which are testing positive for West Nile virus.

Compared with this time last year, the York County West Nile Virus Program — under Penn State Extension — has already collected 6,000 more mosquitoes, said program administrator Thomas Smith.

"Any time it's a higher population, it's a higher risk of disease," he said.

The program works at the county level to test mosquito populations, with assistance from the Pennsylvania Department of Environmental Protection Vector Management.

Some traps are collecting as many as 1,500 overnight, Smith said.

One hundred mosquitoes can be tested per batch, he said, and 36 batches from 28 traps have returned positive results so far. 

On July 3, positive batches included one in Manchester Township, three in Penn Township, one in Springettsbury Township, three in West Manheim Township and one in York City, Smith said.

As of Tuesday, July 10, Smith reported additional positive batches found in Lewisberry, York City, Springettsbury Township, Penn Township and Hanover — and five batches in Manchester Township.

Thirty to 40 more traps are in the queue for testing, Smith said Tuesday, expecting more positives.

By Thursday, the count was at 38, with positive batches reported from Conewago, Manchester, Newberry, Penn, Spring Garden, Springettsbury, Windsor and York townships, as well as Hallam, Hanover, Lewisberry and York City.

"With the trend that we're seeing, the West Nile situation is going to continue at least through September," he said.

Any hurricanes or tropical storms that crop up through October could also ensure that trend continues, he added. 

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Perfect conditions: Smith said mosquito populations have risen in the county since 2008, after the big housing market crash.

Abandoned houses and stagnant water in unused swimming pools caused a spike in the numbers of mosquitoes.

They flock to standing water in containers as small as a bottle cap or as large as a swimming pool and artificial hiding places such as tires, buckets and tarps because their natural predators are not present, according to a news release.

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Just one of these containers can produce hundreds of thousands of mosquitoes in a year, the release states.

This summer, weather conditions also have contributed to the high reproduction rate.

When program staff began West Nile testing at the beginning of May, only one batch tested positive, Smith said.

But increasing heat causes the mosquitoes to mature faster — only taking five to seven days to move through their life cycles — and on top of that, the virus is more active under warmer conditions, he said.

The county has had a lot of rain recently as well, which is another factor.

In these conditions, 10 female mosquitoes can create a population of more than a quarter of a million in just two weeks, he said.

Last year, rain and heat made York County the third in the state for positive mosquito samples.

More: York County a breeding ground for West Nile virus

No human cases of West Nile virus have been reported yet this year, but from now until the end of September, with more affected populations and more people outdoors, communities are more susceptible.

Spraying for mosquitoes: The program was initiated in 2000 — a year after West Nile was first detected in North America — and since then, staff have worked to control the population, monitoring hot spots and determining which areas have the greatest risk of human infection.

Some areas will be sprayed with insecticide — last week, Lower Windsor Township, and this week West Manheim and Penn townships, Smith said.

To control the adult population, the insecticide will be applied at 0.62 ounce per acre, concentrations that are "significantly below" an in-home commercial insect control product, a news release states.

Program staff will spray Wednesday evening, July 11, in Penn and West Manheim townships. If weather or unexpected events cause a cancellation, the rain date will be Thursday, July 12.

Signs will be posted to remind residents on spray day.

In Penn Township, the targeted area will be the residential sections in the vicinity of Westminster Avenue and Baugher Drive, including Homewood and Plum Creek, according to the release.

West Manheim's spraying will cover the residential areas in the vicinity of Oak Hills, Fairview and Sunset drives, including SpriTrust Lutheran, The Village of Utz Terrace, the release states.

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Prevention: Smith emphasized the importance of cleaning up around houses and removing any vessel that could hold stagnant water to prevent the spread of mosquitoes.

Contacting local municipalities can also be helpful in organizing a communitywide cleanup, a news release states.

To avoid the bite of mosquitoes while outside, Smith recommends using repellents and electric fans, which keep them at bay because they cannot fly in the wind. Residents can also get insecticide to spray on their yards, the release states.

For those who may be infected with West Nile virus, Smith warns that the symptoms are common, starting with headaches and fever, similar to the flu.

The best advice is to go to the doctor to get checked as soon as possible, since it can be treated when caught early, he said.

If the virus progresses untreated, in some cases, it can lead to encephalitis — an infection that results in inflammation of the brain. This can be serious, Smith said, because there is no treatment other than the body's natural defenses. So weakened immune systems of older adults and children can be at greater risk of fatality.

County residents can report concerns with mosquitoes through the state's West Nile website at westnile.state.pa.us, call the West Nile Virus Program at 717-840-2375, or email the program at TLS35@psu.edu.

The state Department of Health, at 1-877-PA-Health, has more information on West Nile and Zika virus symptoms in humans. 

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