West Nile Virus Patient Information Fact Sheet

What is West Nile virus?
West Nile virus is transmitted between birds, animals and humans by infected mosquitoes. It is usually transmitted by the Culex mosquito, which bites between dusk and dawn. In 2002, the virus was also detected in a daytime biting mosquito in Maryland County.

The virus has been detected throughout most of Africa, southern and Eastern Europe, the Middle East, parts of the Far East, and Russia. The virus was found in North America for the first time in 1999 when there was an outbreak in New York affecting about 60 people. In 2012, a total of 5,674 cases of West Nile virus including 286 deaths were reported to the CDC.

What are the symptoms of West Nile virus?
Most people with this infection will not have any symptoms at all; some will experience a mild flu-like illness (eg, headache, fever, body aches) for a few days. However, a small number of people (fewer than 1%) may develop severe illness with encephalitis or meningitis (swelling around the brain). This can cause severe headache, disorientation, convulsions and coma. Symptoms of severe disease may last several weeks and neurological effects may be permanent. Very occasionally, West Nile virus infection can result in death, but this is more likely in people >50 years old. The incubation period is usually between 3–14 days.

How is West Nile virus treated and prevented?
There is no specific treatment for West Nile virus. Current management involves treating symptoms only. Infection is thought to lead to long-lasting immunity to this virus.

The risk to travelers going to risk areas is generally low. Those at increased risk of severe disease (>50 years old) should take extra care to avoid mosquito bites. It is sensible to avoid mosquito bites during both day and night. Use an effective repellent on exposed skin. There is no vaccine to prevent West Nile virus ­infection at the moment (but trials are currently in progress).

Further information
Centers for Disease Control and Prevention: http://www.cdc.gov/ncidod/dvbid/westnile/wnv_factSheet.htm

Last Reviewed: June 2013