West Nile fever is a viral disease caused by the West Nile virus. Both animals and humans can become infected. It is mainly transmitted by mosquitoes. In most cases, the disease is asymptomatic. However, around 20% of infected individuals experience flu-like symptoms (sudden fever, headache and back pain, chills, swollen lymph nodes, fatigue) and, in some cases, redness on the torso. Normally, the disease heals on its own after a few weeks without treatment.
In Which Countries Does the West Nile Virus Occur?
The West Nile virus is now found worldwide but is most prevalent in in southeastern Europe, Central Asia, North America, and Africa.However, there has been one case of locally transmitted infection in Switzerland (as of December 2025).
When and How Often Should Vaccinations Be Given?
There is currently no vaccine against the West Nile virus for humans. In the event of an infection, only the symptoms are treated.
How Can You Protect Yourself?
The usual precautions against mosquitoes are recommended for prevention: long-sleeved clothing, mosquito nets, mosquito repellents. You should also avoid touching sick or dead birds.
In addition, you should not donate blood for at least 28 days after traveling to an area where West Nile fever is transmitted.
What Should You Know About West Nile Fever?
The virus is transmitted by mosquitoes.
Human-to-human transmission is very rare.
Severe cases are rare: less than 1% of those infected may develop encephalitis or meningitis. Accordingly, West Nile fever is rarely fatal.
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