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Pennsylvania West Nile Control Program 2000 Year End Report

About the Virus

West Nile virus, named for the region in Uganda where it first appeared in 1937, infects birds, which are bitten by mosquitoes, which in turn bite people and mammals.

It had never been seen in the Western Hemisphere until 62 people became seriously ill and seven died in New York in 1999.

Most people who contract the virus show no symptoms and do not become ill. Those who do get sick may experience headache, high fever, neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness, paralysis and sometimes death. While anyone can get the virus, older people have the highest risk of severe disease.

In 1999, the virus was only detected in New York. In 2000, it was detected in 12 states along the Eastern seaboard.

Surveillance Samples and Test Results




Dead birds



Mosquito pools



Human serology



Human culture



Chicken serum



Horse serum



(rabies negative)



Pennsylvania's Response

In order to detect and reduce the spread of West Nile virus in Pennsylvania, seven state agencies developed a comprehensive early response plan.  These agencies included Pennsylvania departments of Health, Environmental Protection, Agriculture, Aging and Conservation and Natural Resources; Pennsylvania Emergency Management Agency; and Pennsylvania Game and Fish and Boat commissions.

In 2000, West Nile virus was found in mosquitoes, birds and a horse in Pennsylvania.  Fortunately, no people were diagnosed with West Nile virus. These positive results in 19 counties were found through dead bird collection, mosquito collection, and diagnostic testing of suspected cases.

Citizens from more than 59 counties reported more than 3,100 dead birds by calling 1-877-PA-HEALTH.  Of these 1,346 dead birds were suitable for testing. Thirty-seven birds tested positive for West Nile virus. The majority of the positive birds, as well as the ones sent for testing, were crows and blue jays, or corvids.

No positive results were found in the 94 sentinel chicken sites or 17 sentinel horse sites throughout the eastern and northern parts of the states.  More than 4,000 sentinel chicken and 600 sentinel horse samples were collected and tested. A horse at a farm in Dauphin county became ill in late September, and was euthanized. Testing at the Pennsylvania Veterinary Laboratory confirmed WNV infection.

By the end of the season, over 14,000 samples containing almost 500,000 mosquitoes were identified to species. From these samples, 2274 pools of mosquitoes were created and sent for virus isolation, yielding 46 positive pools found in 13 counties. New species of mosquitoes were identified in Pennsylvania raising the total number of species to nearly 60.

PA 2000 surveillance

Tabular view of 2000 PA county surveillance status


Pennsylvania undertook a tremendous effort to develop a complete West Nile surveillance program in a matter of months from the time the virus was identified in the United States.  This effort has put in place the infrastructure to track not only West Nile virus, but other mosquito-borne diseases that may infest North America in the future.

Through direct outreach, Pennsylvania state agencies were able to reach more than 900,000 residents.  Countless more received information through the media, their doctors, their veterinarians, and their municipalities.

In 2001, Pennsylvania will expand its surveillance network.  The 13 counties that had positive mosquitoes in 2000 will begin applying agents to control mosquito larvae when the warmer weather returns.  A total of 25 counties will be in enhanced surveillance, and 26 counties will require routine surveillance.  In addition, sentinel chicken and horse sites will be established in all 67 counties.

As in New York, Pennsylvania can anticipate more positive West Nile results in more mosquitoes and dead birds in 2001.  Pennsylvania will continue to refine and enhance its surveillance program as new technology and information becomes available.

A multi-agency cooperative effort between:

PA Department of Environmental Protection PA Department of Health PA Department of Agriculture

Surveillance Results:

  2000  |  2001  |  2002  |  2003  
  2004  |  2005  |  2006  |  2007  
  2008  |  2009  |  2010  |  2011  
  2012  |  2013  |  2014  |  2015  
  2016  |