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West Nile Virus

A viral disease
What is it?
Photo of West Nile VirusPhoto credit: CDC/ Cynthia Goldsmith

West Nile virus (WNV) is an emerging infectious disease that first appeared in the United States in 1999. The microbe that causes this infection belongs to a group of disease agents known as flaviviruses, which are usually spread by mosquitoes. Other well-known flavivirus diseases include yellow fever, dengue and St. Louis and Japanese encephalitis.

How do I avoid it?

The best and easiest way to avoid WNV is to prevent mosquito bites. When outdoors, use insect repellent and wear long sleeves and pants. Try to stay indoors at dusk and dawn, and make sure your door and window screens are in good condition. Get rid of mosquito breeding sites by emptying standing water from flowerpots, buckets and barrels.

What are the symptoms?

People who contract WNV usually experience only mild symptoms like fever and headache. But if it enters the brain, the virus can cause swelling of tissue in the brain and/or spinal cord, both life-threatening conditions. Severe symptoms can include stupor, disorientation, coma, tremors and convulsions, vision loss, weakness, numbness and paralysis. Symptoms may last several weeks and the neurological effects may be permanent.

How do I get it?

Humans can get WNV from a mosquito that had previously bitten an infected animal. Most severe cases of the disease occur in elderly people and those with weaker immune systems. In a very small number of cases, WNV has also been spread through blood transfusions and organ transplants.

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