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 t is the time of
year when the outdoor season in Canada begins, as we finally move away from a
long, cold winter, to hours of outdoor fun in backyards, parks, and campgrounds.
This time of year also marks the arrival of something far less welcome - mosquitoes
and the threat of West Nile (WN virus). Once regarded as nothing more than a pesky
nuisance, mosquitoes now carry the risk of illness, disability and, in rare cases,
death.
Most people infected with the virus have no symptoms or they have mild, flu-like
symptoms. Sometimes though, the virus can cause severe illness, resulting in
hospitalization and even death.
Although the risk of serious illness is higher for older people and people with
weakened immune systems, anyone can be bitten by an infected mosquito and should
take active steps to protect themselves and their communities. It is very important
to reduce the risk to you and your family by taking steps to avoid mosquito
bites.
Recently, scientists have discovered WN virus can be transmitted
in other ways, including blood
transfusions and organ/tissue transplants. The risk of getting WN virus this
way is considered to be quite low. There is also evidence that pregnant
women can pass the virus to their unborn babies and that the virus may be
passed through breast
milk. In addition, laboratory workers who handle infected specimens can get
WN virus through needle punctures or cuts.
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What is West Nile virus? |
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WN virus
is a mosquito-borne virus that is maintained in a transmission
cycle involving bird and mosquito species. It was named after
the West Nile region of Uganda, where it first appeared in 1937.
Since then, outbreaks of the virus have occurred in Egypt, Israel,
South Africa, parts of Asia and Europe and now North America.
WN virus was first detected in the United States in September
1999 during the investigation of an outbreak of encephalitis
in humans in New York City. It was found in Canada for the first
time during the summer/fall of 2001.
During 2002, more than 4,000 people in North America became
ill and 263 people died after being infected with WN virus.
This is the largest outbreak of WN virus infection ever
recorded. In Canada, there was WN virus in five provinces (Nova
Scotia, Quebec, Ontario, Manitoba, Saskatchewan), including
confirmed cases of human infection in Ontario and Quebec. For
details about WN virus activity, see Public Health Agency of Canada's WN virus Monitor, at http://nile.healthcanada.net. |
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There is no evidence to suggest that people
can get WN virus by touching or kissing someone who is infected, or
from being around a health care worker who has treated an infected
person. Nor is there evidence that the virus can pass from infected
animals to people, including horses and pets.
Who is at risk?
Anybody can have serious health effects with WN virus infection;
however, people with weaker immune systems are considered to be at greater risk
for serious health effects.
- Older people.
- People with chronic diseases, such as cancer, diabetes, alcoholism, or heart
disease.
- People that require medical treatment that may weaken the immune system,
such as chemotherapy.
Although individuals with weaker immune systems are at greater risk, WN virus
can cause severe complications for people of any age and any health status. This
is why it is so important to reduce the risk of getting bitten by mosquitoes.
Anyone exposed to mosquitoes in an area where WN virus has been detected is
at some degree of risk for infection.
Reduce your risk!
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Bird watch |
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Mosquitoes
get the virus through feeding on infected birds and then transmit
the virus to humans through mosquito bites. Not all of the 74
species of mosquitoes in Canada carry WN virus, but it is more
common in species that feed on birds. The virus has been found
in more than 150 bird species in North America. Some species
may have no obvious signs of illness when infected. The most
susceptible birds are crows, blue jays, gray jays, magpies and
ravens.
Keep an eye out for dead birds in your community. If you see anything unusual-
especially dead crows, ravens, jays or magpies- contact your local or provincial
health authority. Information on dead bird surveillance in Canada is tracked
by the Canadian
Cooperative Wildlife Health Centre. The Canadian
Food Inspection Agency will monitor WN virus in animals other than birds,
with a particular focus on horses.
It takes about two weeks before the mosquito is capable of transmitting
the virus to a human or animal. There is some evidence that
female mosquitoes may be able to transfer WN virus to their
offspring, but researchers are still looking into this possibility. |
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To avoid being bitten by mosquitoes, you can take action on
two fronts:
- Minimize your exposure to mosquitoes:
- Mosquitoes can bite at anytime - day or night - depending on where
you are in Canada. Contact your local public authority to find out when
you are most at risk.
- When going outdoors, use insect repellents that contain DEET
or other approved ingredients.
- Wear protective clothing such long-sleeved shirts, long pants and a
hat. Light coloured clothing is best because mosquitoes tend to be more
attracted to dark colours.
- Make sure that door and window screens fit tightly and have no holes
that may allow mosquitoes indoors.
- Eliminate mosquito breeding sites around your home and cottage:
Mosquitoes lay eggs in standing water and it takes about four days for
the eggs to grow into adults that are ready to fly. Even a small amount of
water, for example, in a saucer under a flower pot, is enough to act as a
breeding ground. As a result, it is important to eliminate as much standing
water around your property as possible by:
- Regularly draining standing water from items like pool covers, saucers
under flowerpots, recycle bins, garbage cans etc.
- Remove old unused items from around your property including old tires,
which have a tendency to collect water.
- Change the water in wading pools, birdbaths, pet bowls and livestock
watering tanks twice a week.
- Cover rain barrels with screens.
- Clean out eaves troughs regularly to prevent clogs that can trap water.
- If you have an ornamental pond, consider getting fish that will eat
mosquito larvae.
What about pesticides?
Over-the-counter products that are designed to get rid of garden pests are
not effective for overall mosquito control. For other pesticides, only workers
who are licensed by provincial authorities and are trained in the safe use of
pesticides can carry out mosquito control programs. Decisions on whether or
not to use pesticides to control the spread of WN virus in your community will
be made by local and provincial health authorities. For more information, see
the Public Health Agency of Canada information sheet "Using
Pesticides to Control Mosquitoes".
West Nile virus symptoms
What to watch for
Many infected people do not get sick and show only mild symptoms or none at
all. When infection does cause illness, symptoms
will usually appear within two to 15 days. The extent and severity of symptoms
vary widely from person to person.
Mild symptoms:
- Fever
- Headache
- Body aches
- Mild rash
- Swollen lymph nodes.
For those with weakened immune systems WN virus can develop into encephalitis
(swelling of the brain) or meningitis (inflammation of the lining of the brain
or spinal cord). These conditions can be fatal.
Severe symptoms:
- Rapid onset of severe headache
- High fever
- Stiff neck
- Nausea or vomiting
- Difficulty swallowing
- Drowsiness
- Confusion
- Loss of consciousness
- Lack of coordination
- Muscle weakness
- Paralysis.
Anyone who has a sudden onset of these symptoms should seek immediate medical
attention.
During 2002, several other symptoms of WN virus were identified including movement
disorders, parkinsonism, poliomyelitis-like syndrome and muscle degeneration.
Because WN virus is an emerging disease, the long-term effects are not fully understood.
Studies to date show that some people with serious symptoms and health effects
recover completely, while others experience prolonged health problems.
These problems can include:
- Physical effects- long-term muscle weakness and paralysis, fatigue
and headache
- Cognitive effects-confusion, depression, concentration problems and
memory loss
- Functional effects-difficulty making meals, going out, shopping or
other tasks.
Scientists do not know why some people recover while others continue to have varying
degrees of health problems.
Is there a cure on the horizon?
There is currently no specific treatment, medication or cure for the virus
although many of the symptoms can be treated. At this time, there is no licensed
vaccine to protect people against WN virus. In the United States, the National
Institute of Allergy and Infectious Diseases (NIAID) has supported research
to develop a vaccine against WN virus, with human trials to begin this year.
The Public Health Agency of Canada is monitoring these developments closely.
For more information:
- West Nile general
information
- West
Nile Surveillance Information. Public Health Agency of Canada's most current information
on WN virus, and the measures that government and the provinces are taking
to reduce the WN virus.
- Public Health Agency of Canada information sheets on West Nile Virus - April 2003
- List of approved insect repellents and ways to reduce mosquito populations
from the Pest
Management Regulatory Agency (click on Mosquito Control), or call
1-800-267-6315 (toll-free in Canada).
- Contact
information for reporting dead birds from the Canadian Cooperative Wildlife
Health Centre
- West
Nile Virus and animals
- Health Canada's on-line publication, It's
Your Health
Provincial websites:
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This article was prepared by 
