York County a breeding ground for West Nile virus

Jason Addy
York Dispatch

York County is a hotbed for the West Nile virus this year, ranking third in the state for positive mosquito samples.

Of the 718 mosquito samples that have been found to contain the virus in 2017, 60 of them were taken in York County, according to statistics from the Pennsylvania West Nile Virus Control Program.

Officials from the state Department of Environmental Protection and Penn State Cooperative Extension collected two dozen positive samples from 11 municipalities during a “mosquito surveillance” sweep of the county from July 24 to July 28.

West Nile virus is transmitted through a cycle. An infected bird is bitten by a mosquito that then goes on to bite people.

From July 28 to Aug. 4, officials found 22 additional positive samples from mosquitoes in seven municipalities.

The 46 positive samples over that week-and-a-half span include 13 in Springettsbury Township, 11 in Manchester Township and four in York City, according to the statistics.

Pennsylvania Physician General Rachel Levine announced this year's first human case of West Nile virus in Pennsylvania on Tuesday, Aug. 8, after the virus was detected in a Montgomery County resident.

"Detecting the first human case of West Nile virus this year serves as a great reminder for Pennsylvanians to take the proper precautions when they are outside or near areas where mosquitoes are prevalent," Levine said.

Spraying: After the latest round of tests, York County trails only Philadelphia and Delaware counties for the number of mosquito samples containing West Nile virus, according to Thomas Smith, West Nile virus program administrator at the Penn State York County Extension, which conducts mosquito testing and monitoring.

Penn State Extension West Nile Virus Program administrator Thomas Smith demonstrates the trap used to collect mosquitoes for research. A mix of straw, sour milk and tap water are fermented for a week before being used to lure mosquitoes to the trap, where they are sucked in by a fan, frozen and studied. Dawn J. Sagert photo.

Smith said southcentral Pennsylvania is particularly susceptible to infected mosquitoes, in part because of the amount of rain and heat the area has seen this summer.

As a result of the elevated number of positive samples at the end of July, crews sprayed pesticides in Manchester Township the night of Aug. 2, Smith said.

Crews spray the pesticides at night to avoid causing harm to bees and other pollen-collecting insects, Smith said.

There are 31 types of mosquitoes in York County, but the types that transmit West Nile virus are active primarily at night, Smith said.

Community cleanup: The top three types of mosquitoes testing positive for the virus are known to lay their eggs in “human-made containers,” so the best way for people to fight the virus is to put away anything around their homes and yards that can collect water, Smith said.

“The more we clean up, the less opportunity the mosquitoes have to lay eggs,” Smith said. “If people aren’t cleaning up, then there’s no hope of actually reducing the mosquito population.”

West Nile virus is often found in open containers left in backyards.

Pesticides only kill adult mosquitoes that are flying while crews are spraying, Smith said, reiterating the need to stop mosquitoes from breeding.

In just two weeks, 10 female mosquitoes can multiply into more than 250,000 mosquitoes, given the right weather conditions, Smith said. 

“That’s going on in everyone’s backyard. That’s why we have all these issues,” Smith said, calling the spike in positive samples "very much a human-created condition."

Contracting the virus: West Nile virus is primarily found in birds, but many species have developed immunities to the virus over the last hundred-plus years, Smith said.

The types of mosquitoes that transmit the virus prefer to feed on birds, Smith said, but once the mosquito populations begin to exponentially increase, they look for other sources, such as humans, for their “blood feed.”

Most people who contract West Nile virus will experience symptoms similar to the flu or a cold, but several groups of people are at a higher risk, Smith said.

People under 12 and over 50 and those who have a compromised immune system from another health issue might be more likely to suffer severe reactions.

These groups should try to avoid contact with mosquitoes that might have West Nile virus by wearing long sleeves while outside and limiting outdoor activities at night, Smith said.

Mosquito-repellent candles and electric fans will help keep mosquitoes at bay, Smith said.

Smith said the mosquito season usually drops off in September, though it could run into October if the warm weather continues or a tropical storm hits the area.

— Reach Jason Addy at jaddy@yorkdispatch.com or on Twitter at @JasonAddyYD.