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 Québec 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, in Uganda (Africa).

WNV infection has been a reportable disease in Québec since 2002. Many cases of the infection have been reported in the province since.


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

However, some people do have symptoms, which appear 2 to 14 days after being bitten by a mosquito.

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:

  • Gastrointestinal symptoms
  • Muscle weakness or pain
  • Rashes
  • Neck stiffness
  • Confusion and disorientation

When to Seek Medical Help

Consult a doctor immediately if you experience the following:

  • Severe or unusual headaches
  • High fever
  • Stiff neck
  • Confusion or disorientation
  • Muscle weakness


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

The capacity to fight the virus depends on your health status and age. This capability decreases with age.

A serious West Nile virus infection generally requires hospitalization. Health care aims to stabilize the infection and improve health status.


In less than 1% of people with WNV, the infection can turn severe and lead to neurological problems, such as meningitis (an infection of the membranes covering the brain), encephalitis (inflammation of the brain) or paralysis of the lower limbs. As a result of an infection leading to neurological impairment, permanent neurological damage has sometimes been reported.

In rare cases, WNV causes death.


WNV is transmitted 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 Québec, Héma-Québec tightly controls the quality of donated blood.

Anyone can contract WNV. People who work or spend a lot of time outdoors are most at risk of getting infected. The risk of WNV infection is as high in the city as 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

People at Risk

Adults aged 50 years and older and those with underlying medical conditions or weakened immune system, are at greater risk of developing a severe form of the disease.

Special Conditions

In Québec, WNV infection is a mandatory reportable disease. Laboratory managers and doctors who identify or diagnose a case of WNV infection must notify public health authorities.