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Chester County Press

The West Nile Virus: A cause for local concern?

08/06/2014 02:10PM ● By Lev

The West Nile virus was first detected in the United States in 1999, and in Pennsylvania a year later.

By Richard L. Gaw

Staff Writer

The Pennsylvania West Nile Virus Control Program has conducted 346 mosquito samples in Chester County this year, and of them, 116 have been tested for presence of the virus. Of those, four have tested positive, and on July 10, the Chester County Health Department sent out a written statement saying that the presence of the West Nile Virus had been detected in West Goshen Township.

On July 16, a mosquito sample tested positive for West Nile Virus in Downingtown Borough. The virus has also been detected in mosquito samples collected in Easttown, Treddyffrint and Uwchlan Counties this year, as well as in Berks, Montgomery, Philadelphia and Bucks Counties. This year alone, the program has verified that 64 positive samples of the virus have been detected in nearly half of Pennsylvania's 67 counties.

As the calendar begins its slide into the lazy, hazy days of August and September, and as the waft of backyard barbecues and chlorinated pools drifts into Chester County's days and nights, are individuals and families relegated to fearing that their summer will be impeded by virus-carrying mosquitoes? In other words, is there reason to worry?

Not really, authorities are saying.

"The detections throughout Chester County of the West Nile Virus (WNV) are not a cause for major concern, as these detections are fairly standard for this area and this time of year," said Jeanne E. Casner, County Health Director for the Chester County Health Department [CCHD]. "As context, there were 61 and 142 positive mosquito samples in 2012 and 2013, respectively.  There are fluctuations from year to year; however, this year is average."

The chance of contracting West Nile Virus from an infected mosquito is small and chances of becoming seriously ill are even smaller. Most people bitten by a mosquito carrying the virus aren't in danger, given that the virus can only be transported to humans when a mosquito's salivary gland reaches the person's blood. Even then, three in four people fight off the virus. Only one in 150 people who become infected with the West Nile virus develop a severe illness with reports of high fever, confusion, severe headache, and stiff neck. When symptoms do occur, they start three to 15 days after the mosquito bite.

The West Nile virus, first discovered in Uganda in 1937, has since spread to many parts of the world and was first detected in the United States in 1999, and in Pennsylvania a year later. The United States is in the midst of the largest outbreak of West Nile Virus since 1999, the Center for Disease Control announced recently. So far this year, more than 1,100 cases of human West Nile infection have been reported, about half of them in Texas, and all told, about 40 people have died from the virus. More cases are expected, since West Nile virus infections generally peak in late August and September.

Close to home, Chester County had one confirmed human case in 2012, the first since 2008. In 2012, 146 Mosquito samples tested positive for West Nile Virus in Chester County, compared to 29 positive samples in 2011.

Experts can only speculate about the reasons for this dramatic increase in cases, but it likely has some relation to the record warm temperatures this past winter and spring, followed by a very hot early summer. The breeding cycles of mosquitoes speed up in hotter weather, and the virus seems to replicate faster in warmer temperatures.

And then there are humans. "Human influence, such as leaving tire piles or unmaintained swimming pools, can create breeding grounds that also have a direct impact on the numbers we see, particularly in more suburban and urban areas," Casner said.

The CCHD recommends that individuals take personal precautions to minimize the possibility of being bitten by infected mosquitoes. This includes staying indoors at dawn or dusk when mosquitoes are most active, wearing long sleeve shirts and long pants when outside and using insect repellents when mosquitoes are active. The heightened concern will probably remain until the first frost which usually occurs in mid-October.

The CCHD is working with property owners to eliminate breeding sources, which include standing water, such as tires, pools, buckets and other artificial containers. County regulations prohibit property from being maintained in a condition conducive to the breeding of mosquitoes, and citations may be issued for failure to comply with these regulations. To help stem the flow of mosquito larvae, biological larvicide is used to treat areas of stagnant water that cannot be drained. Larvacide controls mosquitoes in the larval form and is an environmentally safe method of mosquito control.

"It is the individual home or business owner's  responsibility to maintain their property in a manner that is not conducive to mosquito breeding," Casner said. "The county steps in when someone is not maintaining their property, and when necessary enforcement action is warranted in conjunction with our county nuisance regulations."

Casner said that the department's duties relate to education, surveillance and early treatment, such as applying larvacide. CCHD engages staff with these duties as a first resort. Surveillance involves setting traps in which mosquitoes are caught, counted and samples are tested for WNV. As a last resort when all other measures are no longer effective, CCHD staff will engage in other duties such as adult spray treatments.

"While education and information sharing are critical elements to CCHD’s WNV program, the program also includes setting traps in which mosquitoes are caught, counted and samples submitted for testing," Casner said. "In addition, CCHD staff are involved in spraying to eliminate mosquitoes based upon the results of the trappings and tests."

For more information on the West Nile Virus in Chester County, visit or call 610-344-6752.

West Nile Virus Precautions

Residents are encouraged to take the following precautions to reduce mosquito breeding on their property:

 Dispose of open containers that may collect water, such as tin cans, plastic containers, ceramic pots, etc.

 Drill holes in the bottom of outdoor recycling containers so that water will not collect.

 Keep your property clear of old tires.

 Clean roof gutters, particularly if leaves from surrounding trees have a tendency to plug drains.

 Turn over plastic wading pools when not in use.

 Turn over wheelbarrows and don’t let water stagnate in birdbaths.

 Aerate ornamental pools or stock them with fish.

 Clean and chlorinate swimming pools when not in use. A swimming pool left untended by a family on vacation for a month can produce enough mosquitoes to result in neighborhood-wide complaints. Mosquitoes may even breed in the water that collects on pool covers.

 For stagnant pools of water that cannot be removed or drained, homeowners can buy BTI products such as mosquito dunks, which are available at lawn/garden, outdoor supply and home improvement stores. This naturally occurring bacterial product kills mosquito larvae but is safe for people, pets, aquatic life and plants.

Source: Chester County Health Department