West Nile fever is caused by a virus, which is transmitted to humans by the bite of infected mosquitoes. Most people infected will not show any symptoms. Some will experience mild symptoms for a few days, including fever, headache and body aches, nausea and vomiting, and sometimes swollen lymph glands or a skin rash. However, a small number of people (less than 1%) may develop severe illness. The severe symptoms can include high fever, headache, neck stiffness, lethargy, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.55
Occasionally, infected people may die. Most deaths have been reported in those over 50 years old, who generally suffer more severe disease.54c
Transmission54c,55 The virus is usually transmitted to humans by infected mosquitoes. Mosquitoes become infected by feeding on infected birds. West Nile virus is not transmitted from 'person-to-person’ through close contact. However, in 2002 some people in the United States became infected with West Nile virus after receiving blood transfusions.
Geographical distribution54,54b
The virus has been detected throughout Africa, Europe, the Middle East, west and central Asia, and more recently across North America.
Risk to travellers54,54c,55 The risk to travellers going to the USA and other risk areas (eg. Europe) is generally low. Those at increased risk of severe disease (over 50 years old) should take extra care to avoid mosquito bites.
