Take the West Nile Virus Quiz

Other flaviviruses include those that cause yellow fever, Japanese encephalitis, St. Louis encephalitis, and dengue. The West Nile virus was first discovered in the United States in 1999, although it was originally isolated in Uganda in 1937. Besides the United States, it is found most often in Africa, West Asia, Europe, and the Middle East, according to the National Institute of Allergy and Infectious Diseases. In this country, the virus has developed into a summertime illness that continues into the fall, according to the CDC.

An infected bird is bitten by a mosquito, which picks up the virus and passes it on to another bird. Humans can become infected when a female mosquito carrying the virus bites a person. Crows, jays, and magpies seem most vulnerable to the virus, although other birds can become infected. More than 40 species of mosquito can transmit the virus, according to the NIAID. The virus cannot be spread through casual contact such as touching or kissing an infected person. Researchers have found that the virus can be passed from one person to another through blood transfusions or organ transplants, and it also can be passed from mother to child through breast milk.

Infants and people older than 50, particularly those with weakened immune systems, are at risk for becoming seriously ill from the virus. Certain occupations put a person at higher risk for getting bitten by an infected mosquito. These include farmers, foresters, landscapers, gardeners, painters, roofers, pavers, construction workers, laborers, mechanics, and other outdoor workers, according to the CDC.

Up to 20 percent of people infected with the virus will develop some of these symptoms: fever, headache, body aches, nausea, vomiting, swollen lymph nodes, and a skin rash, according to the CDC. These symptoms will develop three to 14 days after a bite by an infected mosquito. Four out of five people infected with the virus will not develop any symptoms at all.

About one person in 150 will develop severe illness after getting infected by the West Nile virus. This is called West Nile encephalitis or West Nile meningitis, depending on which parts of the central nervous system are affected. A person with either of these illnesses usually must be hospitalized; in some cases, these illnesses can be fatal. Symptoms of these severe illnesses, according to the CDC, include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis. These symptoms may last several weeks.

No drugs currently are available to treat the infection caused by the virus. No vaccines are available to prevent infection. The only way to prevent infection is to avoid getting bitten by a mosquito. Testing is available that can help diagnose the infection in people who have symptoms of viral encephalitis or meningitis.

Wearing long sleeves, long pants, and socks can help prevent mosquito bites, especially when the clothing is sprayed with an insect repellant such as permethrin. Use products that contain DEET on your skin. Avoid staying outdoors at dawn and dusk, when mosquitoes are more likely to bite. If you open your windows during the summer, make sure they have adequate screens. Drain any standing water around your home. This includes water buckets, pool covers, and flower pots.