West Nile Virus Activity in the U.S.
August 25, 2003
Health Canada's Travel Medicine Program is closely monitoring West Nile
(WN) virus activity in the United States (US). As of August 22, 2003, WN
virus has been detected in birds, mosquitoes, humans and/or horses in at
least 43 states. In most cases, the detection of the virus has been significantly
earlier than in previous years. At least 772 human cases have been confirmed
or are cited as probable, and 17 deaths have occurred. For a list of states
in the US currently reporting WN virus please visit the Centre
for Disease Control and Prevention.
West Nile (WN) virus is a mosquito-borne virus. Mosquitoes transmit the
virus after becoming infected by feeding on the blood of birds, which carry
the virus. Most people infected with WN virus show no symptoms or only mild
flu-like symptoms. In rare cases, WN virus can cause meningitis (inflammation
of the lining of the brain and spinal cord) or encephalitis (inflammation
of the brain). The elderly, the very young and those with suppressed immune
systems are most at risk for severe illness.
In September 1999, New York City experienced the first confirmed outbreak
of WN virus ever reported in North America. Sixty-two human cases were confirmed
with seven deaths, including one Canadian who travelled to New York City.
WN virus was detected for the first time in Canada in 2001, in birds in
the province of Ontario. The first human case in Canada was reported from
Ontario in September of 2002. To date this year, Canada
has reported WN activity in the provinces of Quebec, Ontario,
Manitoba, Alberta, New Brunswick, and Saskatchewan, with 6 confirmed human
cases. Health Canada was recently notified by the Province of Nova Scotia
of a probable case of WN in a returning Canadian traveller from the US.
Recommendations for Travellers
Canadian's travelling to areas in the U.S. where WN activity is being
reported are advised to use personal insect precautions at all times while
outside to avoid being bitten by mosquitoes. WN virus can be transmitted
by both dusk-to-dawn and day-time biting mosquitoes.
To reduce your exposure to mosquitoes, consider the following measures:
- remain in well-screened or completely enclosed, air-conditioned areas;
- wear light-coloured 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 diethyltoluamide
(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.
Children and DEET
In rare instances, application of insect repellents with DEET has been
associated with seizures in young children (only 14 cases 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 3 to 4
hours. Therefore, in children, DEET in a concentration of not more than 10%
should be applied sparingly to exposed surfaces only and washed off after
the 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 < 2 years of age is not recommended. However,
as a result of Health Canada's Pest Management Regulatory Agency's (PMRA)
re-evaluation of DEET and consultation with the Canadian Pediatric Society,
PMRA now recommends the following:
- on children < 6 months of age:
insect repellents containing DEET still not be used;
- on children aged 6 months to 2 years:
the use of 1 application per day may be considered in situations where a
high risk of complications from insect bites exist the product be applied
sparingly and not be applied to the face and hands; only the least concentrated
product (10% DEET or less) should be used prolonged use be avoided;
- on children between 2 to 12 years of age:
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 and Control and the
National Microbiology Laboratory of the Public Health Agency of Canada,
Health Canada; Pest Management Regulatory Agency, Health Canada
For more information on WN virus, personal insect precautions and surveillance
activities in Canada developed by the Centre for Infectious Disease Prevention
and Control and the National Microbiology Laboratory of the Public Health Agency of Canada of Health Canada, go to http://www.hc-sc.gc.ca/dc-ma/wnv-vno/index_e.html.
Recently, the government of Nova
Scotia announced the first probable human case of WN virus
in the province, which was contracted in the United States. For more information
regarding this incident, please visit the Nova Scotia Department of Health
web site.
For more information on repellents and DEET use, go to: http://www.pmra-arla.gc.ca/english/consum/insectrepellents-e.html 
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