West Nile Virus What is West Nile virus? West Nile virus is a virus that can infect humans, birds, horses and mosquitoes. Infection from this virus is most commonly found in Africa, Europe and the Middle East. The virus has spread to the United States, where it has been reported in 47 states and Washington, D.C. How is West Nile virus spread? West Nile virus is most often spread by mosquitoes. Mosquitoes become infected by biting birds that carry the virus. People can get West Nile virus when an infected mosquito bites them. This happens most often in the warm-weather months of spring, summer and early fall. You cannot get West Nile virus from another person or from your pet. During the 2002 West Nile virus epidemic in the United States, a few people got the virus through blood transfusions and organ transplants. However, the risk of getting the virus in these ways is low. Doctors are not sure if West Nile virus can be passed from a pregnant or breastfeeding woman to her baby. What are the symptoms of West Nile virus infection? Most people who are infected with West Nile virus have no symptoms. Others may have only a mild illness. Symptoms usually occur 3 to 14 days after a person is bitten by an infected mosquito. They may include slight fever, headache or rash. Symptoms of severe illness include sudden, severe headache, high fever, stiff neck, confusion, weakness and coma. These symptoms may last for several weeks. Contact your doctor if you have any of these symptoms and have recently been bitten by a mosquito.  In rare cases, West Nile virus causes a disease such as a swelling of the brain called encephalitis (say: "en-seff-uh-lie-tuss"). This can lead to permanent brain damage or death. Who is at risk for infection with West Nile virus? People who live where West Nile virus has been found in humans, birds, horses or mosquitoes are at risk for infection. (See the box below for a list of states in the U.S. that have had the most reported cases of West Nile virus infection.) However, even in areas where the virus has been reported, it's very unlikely that a person will get sick from a mosquito bite. People 50 years of age and older, and people with weakened immune systems are at greatest risk of becoming severely ill from West Nile virus. Less than 1% of the people who do get infected become severely ill.  The following states have had the most cases of West Nile virus reported to the Centers for Disease Control and Prevention (CDC): California, 771 Arizona, 391 Colorado, 276 Texas, 158 Louisiana, 102 New Mexico, 88 Illinois, 57 Mississippi, 51 South Dakota, 51 Nebraska, 49 How many people with severe West Nile virus infection die? In 2004, 88 people in the U.S. died of severe illness caused by West Nile virus.   Is there a treatment for West Nile virus infection? There is no specific treatment for West Nile virus infection. People who experience mild symptoms usually get better without any medicine after a few days. People with severe illness may be hospitalized and given intravenous (IV) fluids. They may need to be on a machine called a ventilator to help them breathe. Their doctor also will try to keep them from getting other infections, such as pneumonia. Is there a vaccine for West Nile virus? There is no vaccine to prevent West Nile virus in humans yet. How can West Nile virus infection be prevented? The best way to avoid infection with West Nile virus is to reduce the number of mosquitoes around your home and neighborhood. The following are a few things you can do: Get rid of standing water in birdbaths, ponds, flowerpots, wading pools, old tires and other places where mosquitoes might breed. Garden supply stores carry products to keep mosquitoes from breeding in small ponds. Repair any tears in window screens, and porch and patio screens. Stay indoors during dawn, dusk and early evening hours. If you go outdoors at these times, wear shoes and socks, long pants and a long-sleeved shirt. Loose-fitting, light-colored clothing is best. If you go outdoors, use an insect repellent that contains DEET. Apply it according to the directions on the label. Talk to your doctor before you use insect repellent on your child. Your doctor can give you more information on what type and strength of repellent to use.  Source West Nile Virus in the United States: An Update on an Emerging Infectious Disease (American Family Physician August 15, 2003, http://www.aafp.org/afp/20030815/653.html)