West Nile Virus


The West Nile Virus (WNV) belongs to the Flaviviridae family. It is transmitted to humans and animals through the bite of infected Culex mosquitoes which are active from dusk to dawn. The mosquitoes acquire the virus from feeding on infected birds. Human to human transmission does not occur.


West Nile Virus is commonly found in North America, Europe, Africa, the Middle East, and west Asia. Long-term travellers visiting endemic areas are at risk. Older persons and those with a weakened immune system or pre-existing health conditions are at increased risk of getting ill. Peak transmission occurs during summer months.


The majority of cases are asymptomatic – persons do not exhibit symptoms. Approximately 1 in 5 people have symptoms which include a fever, headaches, nausea, vomiting, muscle aches, including a rash (typically on the torso) and swollen glands. Symptoms usually last a few days to several weeks. More severe symptoms of the illness include high fever, disorientation, tremors, convulsions, paralysis, and coma that can cause neurological damage. In rare cases the illness can be fatal. Treatment includes supportive care of symptoms and prevention of secondary infections.


Travellers going to areas with outbreaks of West Nile Virus should take measures to prevent mosquito bites. There is no preventive medication or vaccine against West Nile Virus for humans.

  • Use a repellent containing 20%-30% DEET or 20% Picaridin on exposed skin. Re-apply according to manufacturer's directions.
  • Wear neutral-coloured (beige, light grey) clothing. If possible, wear long-sleeved, breathable garments.
  • If available, pre-soak or spray outer layer clothing and gear with permethrin.
  • Get rid of water containers around dwellings and ensure that door and window screens work properly.
  • Apply sunscreen first followed by the repellent (preferably 20 minutes later).
  • For more details, see IAMAT's insect bite prevention.

West Nile Virus images, life cycle, and distribution maps: Infection Landscapes

Information last updated: February 23, 2021. 

  • Campbell GL, Staples JE, Sejvar JJ, Fischer M. West Nile Virus Disease. In: Jong, E; Stevens, D, eds. Netter’s Infectious Diseases. New York: Saunders Elsevier; 2012: 554-559.
  • Wertheim, Heiman; Horby, Peter; Woodall, John, eds. Atlas of Human Infectious Diseases. Oxford: Wiley-Blackwell; 2012. 273 p.
  • Centers for Disease Control and Prevention: West Nile Virus
  • European Centre for Disease Control: West Nile Virus
  • Public Health Agency of Canada: West Nile Virus
  • World Health Organization: West Nile Virus Fact Sheet No. 354

  • Risk of West Nile Virus is present in the following countries: