Issue 7: Spring 2001 page 6

The Facts Behind West Nile Virus
By Kristen Allen, Natural Resources Specialist

West Nile Virus was first isolated in the West Nile province of Uganda in 1937. Since that time, it has been commonly documented in Africa, Eastern Europe, West Asia, and the Middle East. It had never been documented in the Western Hemisphere until the summer of 1999, when it broke out in New York City. By the spring of 2000, birds infected with the virus were found in nearly every county of New York, Connecticut, Rhode Island and Massachusetts. During the fall and winter of 2000, the virus appeared to move south as infected birds were found in nearly every county of New Jersey and in several counties of Pennsylvania, Maryland and Virginia.

Although many animals are capable of contracting the virus, birds (mainly crows) are the only animals capable of infecting mosquitoes, due to the potential for extremely high virus levels in the blood. Virus levels in birds will remain at adequate levels for transmission for only 3-4 days before the animal either dies or recovers. The virus can then be transmitted to humans only when bitten by an infected mosquito. Although the virus has been found in up to eleven species of mosquitoes, the main vector species associated with the outbreak in New York City is Culex pipiens molesta.

Symptoms and Risk
Bird infections are a very sensitive early detection device for the virus and don't necessarily indicate that there are infected mosquitoes in the area. In 2000, infected mosquitoes were found in New York, New Jersey, Connecticut, and Massachusetts. However, even in areas with infected mosquitoes, much less than 1% of mosquitoes are infected. Assuming a mosquito is infected, 1% of people who get bitten and infected will become ill. Documented human illnesses caused by the virus in 2000 totaled 17 and were found only in northern New Jersey and New York. A mild infection includes such symptoms as fever, head and body ache, skin rash and swollen lymph nodes. More severe infections may also include high fever, neck stiffness, stupor, disorientation, coma, tremors, muscle weakness, paralysis, and very rarely, death. Among those with severe illness due to West Nile Virus, fatality rates range from 3 to 15% and are highest among the elderly.

Treatment and Surveillance
Mosquitoes are a valuable part of the natural food chain in many types of ecosystems. They serve as an important food source for many kinds of wildlife such as other insects, fish, birds and bats. In this way, they add to the overall health of the ecosystem. Using pesticides to control mosquitoes may, in addition to limiting a valuable link in the food chain, damage other insect populations. For this reason, mosquitoes and other native species are not typically controlled on National Park Service lands, except in certain instances. These include extreme human health risks defined by the Center for Disease Control. In the case of West Nile Virus, the National Park Service has authorized mosquito control in two parks in the New York City area. However, it has put the majority of its resources into mosquito surveillance to monitor mosquito populations for infected insects. The National Park Service will begin monitoring mosquitoes this spring in parks from Maine to Virginia. The Virginia Department of Health is also conducting surveillance in the Tidewater region, the part of the state known to inhabit the highest levels of mosquitoes.

How to Protect Yourself
Although infected mosquitoes have not yet been found in Virginia, it is unknown what the upcoming spring and summer will hold for West Nile Virus. Richmond National Battlefield Park will remain up to date on the associated news and research findings and will react accordingly. However, there are many things you can do to protect yourself from the possibility of being infected. First, remove or empty any containers around your home which may collect water. Artificial habitats such as these form larval grounds for mosquitoes that are predator free. Second, stay indoors during dawn, dusk and early evening. These are the primary feeding times for most mosquitoes. Third, wear long sleeves and pants when outside, along with insect repellents containing 35% DEET.

For more information on West Nile Virus, visit the Center for Disease Control's website or contact your state or county Department of Health.

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Last updated: February 26, 2015

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