West Nile Virus
Updated: October 2001
Know before you go!
Infectious diseases not necessarily common in Canada can occur and may even
be widespread in other countries. Standards of hygiene and medical care may
differ from those at home. Before departure, you should learn about the health
conditions in the country or countries you plan to visit, your own risk of
disease and the steps you can take to prevent illness.
The risk is yours
Your risk of acquiring a disease depends on several factors.
They include: your age, gender, immunization status and current state
of health; your itinerary, duration and style of travel (e.g., first
class, adventure) and anticipated travel activities (e.g., animal contact,
exposure to fresh water, sexual contact); as well as the local disease
situation.
Risk assessment consultation
The Public Health Agency of Canada strongly recommends that
your travel plans include contacting a travel medicine clinic or physician
6 to 8 weeks before departure. Based on your individual risk assessment,
a health care professional can determine your need for immunizations
and/or preventive medication (prophylaxis) and advise you on precautions
to avoid disease. We can help you locate a travel
medicine clinic closest to your home.
Some facts from the experts
The information below has been developed and is updated in consultation
with Public Health Agency of Canada's Committee
to Advise on Tropical Medicine and Travel (CATMAT). The
recommendations are intended as general advice about the prevention of
measles for Canadians travelling internationally.
Disease profile |
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West Nile (WN) virus is a mosquito-borne flavivirus that can cause flu-like
symptoms in infected individuals. In rare cases, it can lead to meningitis
(inflammation of the lining of the brain and spinal cord) or encephalitis
(inflammation of the brain). WN virus was first isolated in 1937 in the
West Nile province of Uganda.
Transmission
West Nile virus is spread to humans by the bite
of an infected mosquito. A mosquito becomes infected by feeding
on the blood of a bird that carries the virus. There is no evidence
to suggest that WN virus can be transmitted from person to person.
Many mosquito species can become infected with
WN virus. Culex pipiens, Culex restuans and Culex
salinarius mosquitoes, which are dusk-to-dawn biters, and Aedes
japonicus and Aedes triseriatus mosquitoes, which
are daytime biters, have been shown to be infected. However, Culex
pipiens and restuans appear to have been the species
most commonly infected during the outbreaks in the eastern United
States in 1999 and 2000.
The number of bird species in North America
that can carry WN virus is not known at this stage, although approximately
76 species were affected during the 1999 and 2000 outbreaks in
the eastern USA. The group that appeared to be most affected was
corvids, such as crows, ravens and blue jays.
In the eastern United States, there have been
cases of WN virus documented in other animals: cat, domestic rabbit,
chipmunk, gray squirrel, striped skunk, bats and horses. For animals
which show symptoms, these could include any combination of the
following: fever, weakness, lack of coordination, muscle spasms,
seizures and/or changes in temperament or personality. There have
been no documented cases of one animal infecting another animal,
or of an animal infecting a human.
Geographic
distribution |
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Outbreaks of WN virus have occurred in several countries
including Egypt, Israel, South Africa, and parts of Asia and Europe.
Recent outbreaks, outside of North America, have occurred in France and
Israel in 2000, Russia in 1999 and Romania in 1996-97.
The first outbreak of WN virus in North America occurred
in and around New York City late in the summer of 1999. There were 62
confirmed cases (mostly elderly people), with seven deaths, including
one Canadian who had visited New York City during the time of the outbreak.
In the summer of 2000, there were 21 confirmed cases in New York City
and the states of New Jersey and Connecticut, resulting in two deaths.
There was considerable WN virus activity in Massachusetts, Rhode Island,
New Hampshire, Maryland, Pennsylvania, Vermont, Virginia, North Carolina
and the District of Columbia (Washington). The virus had been detected
in dead birds, mosquitoes, horses and other animals in a number of counties
in these states.
Symptoms |
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Symptoms can begin 3 to 15 days following the bite of
an infected mosquito. However, most people who are infected with WN virus
show no symptoms at all or may experience only mild flu-like symptoms such
as fever, headache and body aches before fully recovering. Reports from
countries outside of North America indicate that some persons may also develop
a mild rash or swollen lymph glands.
In rare cases, particularly among the elderly, very young,
and those with suppressed immune systems, infection with WN virus can result
in serious illness such as meningitis (inflammation of the lining of the
brain and spinal cord) or encephalitis (inflammation of the brain). Symptoms
for these conditions could include rapid onset of severe headache, high
fever, stiff neck, vomiting, drowsiness, confusion, muscle weakness, and
loss of consciousness (coma). People who have a sudden onset of these symptoms
should seek medical care immediately. In some people with serious illness
death may occur.
Treatment |
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Although there is no specific treatment, medication
or cure, many of the symptoms and complications of the disease can
be treated. Most people who are infected with WN virus recover. There
is no vaccine for WN virus at this time.
Prevention and personal precautions |
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The risk of becoming seriously ill as a result of infection with WN
virus is low.
Recommendations
Personal measures to avoid
mosquitoes
Public Health Agency of Canada encourages travellers to areas with West Nile
virus activity in mosquitoes, birds and particularly in humans, to take
personal insect precautions at all times while outside to avoid being
bitten.
To reduce your exposure to mosquitoes, consider the following
measures:
- remain in well-screened or completely enclosed, air-conditioned areas;
- wear light-colored clothing with full-length pant legs and sleeves;
and
- use insect repellent on exposed skin.
The use of insect repellent on exposed skin is strongly
recommended. Of the insect repellents registered in Canada, those containing ‘N,
N diethyl-m-toluamide' (DEET) are the most effective. Although the concentration
of DEET varies from product to product, repellency rates are largely
equivalent. In general, higher concentrations protect for longer periods
of time, but there is little advantage in the duration of repellence
with DEET concentrations > 30%, and there may be additional risk of
toxicity with higher concentrations. New microencapsulated products containing
33% DEET are registered in Canada, and they should provide 8 hours of
protection.
Children and DEET
In rare instances, application of insect repellents with DEET
has been associated with seizures in young children (14 cases have been
reported in over 30 years of DEET use and billions of applications every
year). The actual concentration of DEET varies among repellents and can
be as high as 95%. However, repellents with DEET concentrations of 10%
are very effective and should last three to four hours. For children, DEET
in a concentration of not more than 10% should be applied sparingly to
exposed surfaces only and washed off after children come indoors.
The likelihood of adverse reactions can be minimized
by the following precautions:
- Apply repellent sparingly and only to exposed skin.
- Avoid applying high concentration products.
- Avoid applying repellents to portions of children's hands that are
likely to contact the eyes or mouth.
- Never use repellents on wounds or irritated skin.
- Wash repellent-treated skin after children come indoors. If a reaction
to insect repellent is suspected, wash treated skin and seek medical
attention.
Labels on DEET-containing products in Canada currently
indicate that the use of DEET on children under 2 years of age is not
recommended. However, as a result of Public Health Agency of Canada's Pest Management
Regulatory Agency's (PMRA) re-evaluation of DEET and consultation with
the Canadian Pediatric Society, PMRA now recommends the following for
children under 2:
on children under 6 months of age:
that insect repellents containing DEET still not be used;
on children aged 6 months to 2 years:
that the use of 1 application per day may be considered in situations where
a high risk of complications from insect bites exists. The product should
be applied sparingly and not be applied to the face and hands; only the
least concentrated product (10% DEET or less) should be used, and prolonged
use should be avoided; on children between 2 and 12 years of age:
that the least concentrated product (10% DEET or less) be used and that it
be applied no more than 3 times per day.
Sources: Centre for Infectious Disease Prevention & Control
and the National Microbiology Laboratory of the Public Health Agency
of Canada.
For
more information on repellents and DEET use, go to: Safety Tips on Using Personal Insect Repellent .
Some things to think about... |
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Most people who are infected with WN virus show no symptoms at all or may
experience only mild flu-like symptoms such as fever, headache and body
aches before fully recovering.
For more information...
- For more information on WN virus, personal insect precautions
and surveillance activities in Canada developed by the Centre
for Infectious Disease Prevention & Control and the National
Microbiology Laboratory of the Public Health Agency of Canada, go to West Nile virus MONITOR .
- For more Know before you go! information, click
here.
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