How it Spreads

West Nile Virus is primarily spread through the bite of an infected mosquito. Mosquitoes become infected when they bite infected birds. The virus eventually finds its way into the mosquito's salivary glands and during its next meal the virus can be passed to humans and animals, where it could make a person sick. View a diagram of how West Nile Virus is spread.
There are also some less common ways to become infected with West Nile Virus, although very few cases are spread in the following ways:

Organ Transplant: West Nile Virus can be passed through transplanted organs.

Blood Donor: All blood donations are tested by Canadian Blood Services for West Nile Virus, which has significantly decreased the risk of West Nile Virus being passed through blood transfusion.  If you are having surgery when mosquitoes are active in BC, and you might need a blood transfusion, discuss the benefits and risks of using blood with your doctor. Visit Canadian Blood Services for more information.

Breast Feeding: West Nile Virus has been found in breast milk of infected mothers, but does not seem to cause any significant illness in breastfed infants. If you are breast feeding, protect yourself from mosquito bites.

Mother to unborn baby: This has occurred in a few cases and at risk mothers should seek the advice of their doctor.  If you are pregnant protect yourself from mosquito bites.

West Nile Virus and Birds

Infections in birds: Most species of birds can carry West Nile Virus. They become infected from the bite of a mosquito that has previously bitten an infected bird. Many species of birds carry the virus for a few days and recover. Birds of the corvid family (crows, ravens, jays) are particularly likely to get sick and will probably die from a West Nile Virus infection within a few days.

Report dead birds: A collection and testing program is in place for dead corvids (crows, ravens, jays, and magpies) and we rely on public reporting of dead bird sightings. Not all dead corvids will be collected, but ALL sightings should be reported so a proper follow-up can be done. To report the sighting of a dead corvid, please call the West Nile Virus Toll Free Hotline at 1-888-WEST NILE VIRUS-LINE (1-888-968-5463).

Although many bird species can be infected with West Nile Virus, members of the crow family (crows, ravens, magpies, jays) have a high death rate when infected. For this reason testing samples of dead crows for West Nile Virus is an effective way of determining when the virus moves into a new area.