WEST NILE VIRUS
Source: Pennsylvania State University, College of Agricultural Sciences, Agricultural Research and Cooperative Extension
- Introduction
- Disease Transmission
- Geographic Distribution
- Symptoms of West Nile Encephalitis
- Diagnosis and Treatment
- Prevention and Control
- Protect Yourself from Bites
- How to Report Dead and Dying Birds
- Using DEET Repellents Properly
The West Nile virus, which can cause encephalitis, is commonly found in humans, birds, and other animals in Africa, Eastern Europe, West Asia, and the Middle East. The virus was first isolated in the West Nile province of Uganda in 1937. The earliest recorded epidemics of West Nile encephalitis occurred in Israel between 1951 and 1954 and again in 1957. Since then, epidemics have been reported in Europe - in the Rhone delta of France in 1962 and in Romania in 1996. The largest recorded epidemic occurred in South Africa in 1974. Most recently, a West Nile encephalitis epidemic was seen in Israel during 2000.
West Nile encephalitis had never been documented in the Western Hemisphere before the late summer of 1999, when an outbreak occurred in the New York City metropolitan area. The virus probably was introduced into the United States by an infected bird or mosquito.
West Nile virus is transmitted by infected mosquitos, mainly Culex and Aedes spp. These mosquitoes become infected after biting infected wild birds, the primary hosts of the virus. The virus circulates and multiplies for several days in a mosquito's blood before penetrating its salivary glands. After an incubation period of ten to fourteen days, an infected mosquito can transmit the virus to both humans and animals while feeding on them.
Most female mosquitoes must take a blood meal before they can lay eggs. A female's persistent search for blood can bring it into houses and yards wher eit may come into contact withe people. Fortunately, very few mosquitoes are infected, even in areas where they carry the West Nile virus, so the chance of being bitten by an infected mosquito is small.
West Nile virus was found in wild birds in four U.S. states in 1999; by the end of 2000, it had been detected in twelve East Coast states and Washington, D.C. From 1999 to 2000 , the number of human cases of symptomatic encephalitis fell from 62 to 21, and deaths declined from 7 to 2. However, the human cases in 2000 occurred in New York, New Jersey, and Connecticut; whereas in 1999, the cases were only in the New York City metropolitan area. In Pennsylvania in 2000, infected birds and mosquitoes were foound in 19 counties, and one horse death was reported.
The incubation period of a West Nile virus infection in humans is usually 5 to 15 days. Most people who are infected with the virus have either no symptoms or mild ones such as fever, headache, body aches, mild skin rash, or swollen lymph glands. A more severe infection, which may lead to encephalitis, includes headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, neurological damage, paralysis, and occasionally death.
All residents living in areas where West Nile virus has been detected potentially can become infected with the virus. However, only a small number of people who become infected will develop a serious case of encephalitis. People over 50 years of age are at greater risk of becoming severely ill because of their declining immune systems. Al who died in 1999 and 2000 were over 68 years of age. Nevertheless, anyone with compromised immune system, regardless of age, is at risk.
There is no vaccine to protect people from the West Nile encephalitis virus, nor is there a specific treatment, medication, or cure. However, the symptoms and complications of the disease can be treated. Severe cases may call for hospitalization, intravenous (IV) fluids and nutrition, airway management, ventilatory support, and prevention of secondary infections such as pneumonia.
You can reduce the number of mosquitoes around your home and neighborhood by eliminating standing water, in which mosquitoes can breed.
- Dispose of any refuse that can hold water - such as tin cans, containers, and in particular used tires. Tires have become the most important mosquito breeding sites in the country.
- Drill holes in the bottoms of recycling containers, and check uncovered junk piles.
- Clean clogged roof gutters every year, and check storm drains, leaky faucets, and window wells.
- Empty accumulated water from wheelbarrows, boats, cargo trailers, toys, and ceramic pots. If possible, turn them over when not using them.
- Do not allow water to stagnate in birdbaths, ornamental pools, water gardens, and swimming pools or their covers. Ornamental pools can be aerated or stocked with fish. Swimming pools should be cleaned and chlorinated when not in use.
- Alter the landscape of your property to eliminate standing water.Keep in mind that during the warm weather, mosquitoes can breed in any puddle of water.
Even though your property may be devoid of mosquito breeding sites, mosquitoes can travel two to three miles from their breeding site in search of a blood meal. Following these tips can reduce your risk of being bitten by a mosquito:
- Make sure window and door screens are "bug tight".
- Use the proper type of light outside: incandescent light attract mosquitoes, while fluorescent lights neither attract nor repel mosquitoes.
- Stay indoors at dawn, dusk, and in the early evening when mosquitoes are most active. If you must go outdoors, wear a long-sleeved shirt and long pants.
- Insect repellents, when applied (sparingly) to exposed skin, deter mosquitoes from biting. Spray thin clothing with repellent since mosquitoes can bite throgh it. Be sure to follow all directions on product labels.
- Mosquitoes are repelled by high winds, so electric fans may provide some relief at outdoor events.
- Vitamin B and "ultrasonic" devices have not been proven effective in preventing mosquito bites.
The Commonwealth of Pennsylvania is encouraging citizens to report dead and dying birds so they can be tested for West Nile virus. This is very important, since birds provide an early warning that the the virus is active in an area. If you see a dead or dying bird, please call the PA Department of Health's toll-free hotline at 1-877-PA-HEALTH (724-3258) for further instructions.
DEET remains one of the most widely used insect repellents. Products containig 10 to 35 percent DEET will provide adequate protectionfor most people under most conditions. The American Academy of PEdiatrics recommends that repellents used on children contain no more than 10 percent DEET. To use a repellent product safely, regardless of its active ingredient, follow these guidelines:
- Verify that the product has an Environmental Protection Agency registration number. Its prescence on the label means the product was approved for use by the EPA.
- Before using any product, read and understand the directions on its label.
- Do not spray a repellent in an enclosed area or near food, and do not inhale aerosol formulations.
- Repellents should not be applied to infants or used by pregnant women.
- Use just enough repellent to lightly cover exposed skin and clothing. Never apply repellents to cuts , wounds, or inflamed and irritated skin. Do not saturate the skin or apply beneath clothing.
- To apply a repellent to your face, first dispense or spray it onto your palms and rub your hands together. Then apply a thin layer to the surface of your skin. Do not place repellent in your eyes or mouth.
- Do not allow children to apply DEET by themselves.
- Do not apply a repellent directly to a child's skin. First apply it to the palms of your own hands and then apply it to the child. Do not apply repellent to children's hands, since they may touch their eyes and mouth, causing irritation.
- DEET can damage some plastics, synthetic fabrics, leather, and painted or varnished materials. DEET does not damage natural fibers such as cotton or wool.
- After applying a repellent, wipe or wash it from your hands.
- A single application of a repellent is sufficient under most conditions. Avoid prolonged or excessive use of DEET.
- Once indoors, wash all treated skin and clothing with soap and water. Wash treated clothing before wearing it again.
- If you suspect that you or your child is reacting negatively to an insect repellent, discontinue its use, wash treated skin, and call the Poison Center. If you must see a doctor, take the repellent with you.
A very small segment of the poulation may be sensitive to DEET and/or other insect repellents. For more information about DEET, contact the National Pesticide Telecommunications Network at 1-800-858-7378.
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