West Nile virus infection
West Nile virus (WNV) is transmitted by mosquito bites to birds. Humans and mammals can also become infected, although about 80% of human infections have no symptoms. Most cases in humans occur between July and September when mosquitoes are active.
About 20% of WNV infections in humans may cause West Nile fever (WNF), characterised by:
- headache
- malaise
- fever
- myalgia
- vomiting
- rash
- fatigue
- eye pain
Less than one per cent may cause West Nile neuroinvasive disease (WNND) that affects the nervous system.
Risk factors include:
- advanced age
- tumours in the brain
- high blood pressure
- blood disorders
- diabetes
- kidney diseases
- alcohol abuse
- genetic factors
The mortality rate among people who develop WNND can be up to 17%.
WNV is usually spread to humans from infected mosquitoes. Mosquitoes get infected by infected birds. Mosquitoes spread the virus, and birds help the virus to grow in numbers. The virus can also spread between humans through blood transfusion and organ transplant. Other ways in which the virus can spread are from mother to child during pregnancy and breast-feeding and through laboratory exposure.
There is no specific treatment for the virus, only supportive care.
Personal protective measures include:
- the use of mosquito nets
- sleeping in screened or air-conditioned rooms
- wearing clothing that covers most of the body
- using mosquito repellent
