FAQ: West Nile Virus (WNV)
» What is West Nile
West Nile virus is spread by the bite of an infected mosquito,
that have feasted on the blood of infected birds, and can infect
people, horses and some other animals. Symptoms usually appear
10 to 14 days after someone has been bitten by a mosquito that
has the virus. Most people who become infected with West Nile
virus will have either no symptoms or only mild ones. However,
West Nile virus infection can sometimes result in severe and fatal
illnesses. Although most people fight off the virus, about one
in 150 suffer serious illness, primarily meningitis (swelling
of the lining of the brain) or encephalitis (swelling of the brain).
» If I live in an area
where birds or mosquitoes with West Nile virus have been reported
and a mosquito bites me, am I likely to get sick?
No. Even in areas where the virus is circulating,
very few mosquitoes are infected with the virus. Even if the
mosquito is infected, less than one per cent of people who get
bitten and become infected will get severely ill. The chances
you will become severely ill from any one-mosquito bite are
» Who is at risk of
In general, wild birds are the largest population infected with
the West Nile virus. Birds do not normally show signs of infection
– they merely act as a host for the virus, however, humans
can also become infected with the virus. People living in an area
where there are virus carrying mosquitoes are at risk of getting
bitten. However, not everyone who is bitten by an infected mosquito
will develop West Nile-most cases are very mild; with flu-like
symptoms or no symptoms at all.
At risk are:
- the very young
- individuals >50 years of age
- individuals with weakened immune systems
- individuals with other medical conditions,
including diabetes, heart disease, or individuals on dialysis.
» What can I do to reduce
my risk of becoming infected with West Nile virus?
Please read our FAQ on "How
to Avoid Mosquito Bites" for information on how to reduce
your risk of getting West Nile virus.
» Can West Nile virus
be transmitted through blood transfusions and organ transplants?
Yes, there have been confirmed cases in Canada and the United
States of West Nile virus being spread through blood transfusions
and organ transplants. The risk of getting West Nile virus through
these procedures is very low, and many believe that the benefits
of these procedures outweigh the risk of becoming infected with
West Nile Virus. If you are scheduled to receive a blood transfusion
or organ transplant, you may wish to discuss your concerns with
your doctor or surgeon. [Source: Health Canada]
» Can West Nile virus
be transmitted by donating blood?
No. Donating blood is a safe procedure and people cannot become
infected when they volunteer to donate blood. If you are experiencing
symptoms of West Nile virus infection (or another illness),
you will be temporarily deferred from donating blood in order
to enhance the safety of the blood supply. Canadian
Blood Services is grateful to those who donate blood in
order to save the lives of their fellow Canadians.
» Can a pregnant woman
pass West Nile virus to her unborn baby?
There has been one known case in the United States of a mother
passing West Nile virus to her unborn baby. In this case, the
baby was born with serious medical problems. However, it is not
known whether the problems were caused by West Nile virus or by
other factors. Since evidence shows it is possible to pass West
Nile virus to an unborn child, pregnant women should take immediate
steps to reduce their risk of mosquito bites if they are in an
area where West Nile virus is active. If they develop symptoms
of West Nile virus infection, they should call their doctor or
health care provider right away. [Source: Health Canada]
» Can West Nile virus
be passed to a child through breast milk?
There is evidence that this is possible. In one case in the United
States, a woman was infected with West Nile virus after the birth
of her child. She breast-fed her baby, and the baby later tested
positive for West Nile virus infection. Laboratory tests determined
that West Nile virus was present in the breask milk. Investigators
looking into the case believe it is unlikely that the baby was
infected by a mosquito bite. They concluded that break milk was
the most likely source of infection. Despite being infected with
West Nile virus, the child had no symptoms and remained healthy.
Women who are breast-feeding their children should contact their
doctors for advice if they have symptoms of any illness, including
West Nile virus. [Source: Health Canada]
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Pfizer Canada Inc.