West Nile Virus (WNV)


The West Nile Virus (WNV) is transmitted through the bite of an infected mosquito. It may be contracted in Canada, USA and several other regions of the world. The virus has been present in Quebec since 2002, particularly in the south regions of the province.

In North America, WNV infections are seasonal. They occur over the summer and through the fall, up until the first frost.

WNV was isolated for the first time in 1937 in the West Nile region of Uganda (Africa).


In most cases, people infected with WNV do not have symptoms. Other have mild symptoms.

The incubation period before symptoms appear is 2 to 14 days after being bitten by an infected mosquito.

The most common WNV infection symptoms include:

  • Headache
  • Fever

These symptoms may be accompanied by:

  • Muscle pain
  • Appearance of pimples
  • Skin rash

When to Seek Medical Help

Consult a doctor immediately if you experience the following:

  • Severe and unusual headache
  • High fever
  • Stiff neck
  • Confusion
  • Muscle weakness


There is no treatment or vaccine for WNV. However, most people infected heal without treatment.

The capacity to fight the virus depends a lot on your health and age. The older you are, the harder it is.

A serious West Nile virus infection generally requires hospitalization. Care is geared towards stabilizing the infection and improving health. 


Less than 1% of people infected experience the following complications:

  • Serious inflammation of the brain (encephalitis) or paralysis of the lower limbs
  • Neurological problems that may become permanent

In rare cases, WNV causes death.

People aged 50 years or older and those with an immune system weakened by other illnesses are most at risk for complications. 


WNV spreads to humans via infected mosquitoes. Mosquitoes become infected when they feed on infected birds. WVN mostly infects birds, but also humans and other animal species such as horses.

WNV is not transmitted when a person is in contact with a bird, an infected animal or another person.

Although the risk is low, WNV can be transmitted during blood transfusion or organ transplant. To reduce the risk in Quebec, Héma-Québec tightly controls the quality of donated blood.

Anyone can contract WNV. People who work or spend a lot time outdoors are most at risk of getting infected. Risk of WNV is high in cities, but is also present in the countryside. 

Protection and Prevention

Avoiding mosquito bites is the best way to prevent WNV infection. Simple measures can be taken to protect yourself from mosquito bites

Special Conditions

In Quebec, it has been mandatory to report West Nile Virus infection cases. Any laboratory staff member or doctor who diagnoses the disease must notify the public health authorities.

Last update: June 8, 2016 1:37 PM


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