West Nile Fact Sheet
West Nile Encephalitis And You
Encephalitis, a virus-induced inflammation of the brain, is not a new occurrence in the United States
or worldwide. In fact, groups of similar viruses such as, St. Louis encephalitis and Eastern Equine
encephalitis have occurred throughout the world for decades. Originally, The West Nile Virus was described
here in the United States as St. Louis encephalitis because of its close likenesses. In the end, it was
determined to be a genetic mutation of the West Nile encephalitis, which was first described in Uganda in
1937. On September 14, 1999, the first human case of this virus had appeared in the Western hemisphere,
in New York City. Historically, this virus had only been found in humans, birds, and other vertebrates in
Africa, West Asia, Eastern Europe, and the Middle East.
Introduction of the virus into the United States most likely occurred through either an infected mosquito
or bird. To date, the list of bird and mosquito species capable of transmitting the virus continues to grow
with a current count of over sixty species of birds and eight mosquitoes. The most common bird carriers here
in the North East include the American crow, pigeon, and American robin. Other vertebrates recently discovered
as carrying the virus include; bats, horses, and raccoons. The mosquito carriers are much more limited at
this time, and the main carrier remains the Northern house mosquito, Culex pipiens, which is quite prolific
in our region.
Since its’ introduction in September of 1999, the virus has spread to twelve states along the Eastern seaboard,
including the District of Columbia and as far as Windsor, Canada. In Pennsylvania alone, seventeen counties have
been identified as having birds or mosquitoes with the virus. To date, there have been no human cases reported
in Pennsylvania. State and Federally funded surveillance programs currently in place will be further enhanced
to monitor for the virus. These programs will continue throughout the 2001 season to monitor the progression
of the virus.
Transmission of the virus from one individual to another occurs when an infected mosquito feeds on the blood
of an unsuspecting host. These viral bodies multiply within the infected mosquito, penetrate the mosquito’s
salivary glands, and are injected into the next host victim. From this point, the virus incubates within the
host for approximately 5 to 15 days, after which symptoms become evident. Symptoms include mild fever, headache,
and general body aches. Advanced progression of the virus may also include stiff neck, disorientation, muscle
weakness, coma, and rarely, death. Currently, there is no vaccine available to combat the virus. People most
at risk for developing the disease include the very young, the elderly, or those with compromised immune
systems. Some people may become infected with the virus and never show any symptoms at all.
How can you protect yourself? First, avoid times of peak mosquito activity, early morning, late evening, or
dusk. These are points in the day, which pose the most risk for individuals to be bitten by mosquitoes.
Secondly, wear light colored, long sleeved clothing and pants to limit skin exposure. Third, make sure all
windows and screens are "bug proof" as well as replacing normal exterior lighting with the yellow "Bug"
lights. Finally, use according to directions, an appropriate insect repellent with 35% or less of
DEET.
Many factors are involved in the continued transmission or movement of the virus from one area to the next
namely, the ability of the mosquito vector and its reservoir host to survive. Factors such as host health,
vector competence, and weather are the major factors to name a few. In the Northeast and the Mid-Atlantic
regions, the ability of an infected female mosquito to survive the winter holds the key to this season’s
viral success. Scientist claim that El Ninó and his sister La Ninã may very well play a major factor in
the virus’ ability to survive. As these systems influence our local weather, the survivability of the virus
and its’ host respond accordingly.
IPM or Integrated Pest Management techniques will greatly help to suppress this spread. Pennsylvania Pest
Management Association members implement the methods of integrated pest management into each pest management
solution they provide their customers. Residents can reduce mosquito numbers by implementing management
practices around the home. Some of these simple practices include eliminating any containers that can hold
standing water such as, tin cans, flower pots, pool covers, and used tires. Cleaning clogged drain gutters
and aerating stagnate ornamental ponds will also add to the reduction process.
Remember, The Pennsylvania Pest Management Association members protect your health, food, home, and help to
improve the quality of life for Pennsylvania residents. For more information on how we can assist you during
this health emergency, please contact us at 800-842-9090 or visit us on the web at
www.papma.org.
Prepared by: Win Higgins, Consulting Entomologist and IPM Chairman, The Pennsylvania Pest Management
Association.
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