The virus, usually transmitted by infected mosquitoes, which become infected when they feed on infected birds, is commonly reported in Africa, Europe, the Middle East, North America and West Asia. Rarely human infections have occurred following organ transplant, blood transfusions and to infants via breast milk. There is one reported case of transplacental (mother-to-child) WNV transmission.
Most infections are asymptomatic. Approximately 20 per cent of people who become infected with WNV develop symptoms, which may include fever, headache, tiredness, body aches, nausea, vomiting, skin rash and swollen lymph glands. An estimated one in 150 persons infected with WNV will develop a more severe form of disease such as encephalitis or meningitis. Serious illness can occur in people of any age, however those over the age of 50 and immunocompromised persons are at increased risk of developing severe illness.
Advice for travellers
Cases in returned UK travellers are rare. However, travellers should practise insect bite avoidance measures day and night when visiting countries where WNV is reported. There is currently no vaccine available to prevent WNV in humans.