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The West Nile Virus: A cause for local concern?

07/23/2014 02:36PM, Published by Lev, Categories: In Print, News



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. 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.

The West Nile 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?


The West Nile virus, first discovered in Uganda in 1937, and since then, it 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 virus is transmitted to humans through the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds, which may circulate the virus in their blood for a few days. The virus eventually gets into the mosquito's salivary glands. The virus may be injected into humans and animals by the bite of an infected mosquito, where it can multiply and possibly cause illness.

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 WNV in Chester County, compared to 29 positive samples in 2011.

The truth is, however, that most people bitten by a mosquito carrying the West Nile 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.


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


Chester County is controlling the mosquito population in ooperation with its residents. Acting on tips, agencies like the CCHD work 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.

The CCHD decides which areas should be treated for mosquitoes through the use of mosquito traps, that are placed in known breeding areas such as past positive locations, parks, sewage treatment plants and areas of concern. Traps are also placed in response to complaints from county residents regarding high numbers of mosquito activity.



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