Health in the Mosquito Season

August 19th, 2008

In Winnipeg, Manitoba, we take our mosquito problems seriously.

Faced with almost 50 varieties of mosquitoes, several of which can potentially carry the possibly lethal West Nile Virus, we need to take them seriously.

Mosquitoes are members of the biting fly family of insects and females need blood in order to produce eggs. The females use a long mouth called a proboscis to obtain blood and eggs are laid in standing water and hatch in about seven days as larvae, eventually these become pupae and finally adult mosquitoes. When the mosquito bites they deliver anti-coagulants to the victim along with assorted enzymes. Most people (but not all!) react to the anti-coagulant and the result is itching and swelling at the site of the bite.

The City of Winnipeg recommends a variety of strategies to deal with mosquitoes:
• Make sure all doors and windows fit properly and have tight-fitting, fine mesh screens.
• Wear long sleeved shirts and long pants that are light coloured and loose fitting.
• Apply an insect repellent that contains DEET. (DEET is not recommended for children under the age of 6 months.) For more information, go the Manitoba Government web site at http://www.gov.mb.ca/health/wnv/.
• Reduce outdoor activity where mosquitoes are abundant and active. This will be in heavily vegetated areas and on days that are calm and humid, particularly near sunrise and sunset.
• Cover baby carriages and strollers with fine mesh netting to protect infants.
(Source: http://www.winnipeg.ca/cms/bugline/mosquitoes/mosquito_information.stm)

In addition home and apartment owners can perform a variety of other simple tasks to reduce the number of mosquitoes. Most effectively they can drain containers of standing water left outside this will deprive larvae of a place to develop.

The West Nile Virus


The good news is that there are a very small number of mosquitoes that can carry the West Nile Virus in Manitoba, most notably the relatively rare Culex tarsalis. According to initial studies in 1999 (when the disease reached North America from Africa) the actual chances of getting infected with West Nile are very low. Between 1% and 3% of the population of Queens in New York showed evidence of exposure after the first outbreak. Of those who did get infected 80% show no symptoms and only 1 in 150 of those who are infected show serious signs of infection like Meningitis or Encephalitis with between 5% and 10% of this final group dying.

In Manitoba the number of serious cases of West Nile is quite low, “The number of serious WNV cases in Manitoba has ranged from 1 to 72 per year since 2003. The number of WNV-related deaths per year has ranged from 0-4.” (Source: http://www.gov.mb.ca/health/wnv/intro.html)

Keeping the Bugs Away


Fortunately West Nile can be prevented simply by keeping the mosquitoes away. Towards that end there are a wide number of options, the chemical DEET (found in most over-the-counter insect repellents, it acts by making it harder for mosquitoes to zero in on carbon dioxide, the normal way mosquitoes hunt) being the most common. However many scientists promote plant-based repellents based on eucalyptus, soy-bean oil and citronella and the Government of Manitoba has information to determine who can safely use each type of repellent. This is available at http://www.wrha.mb.ca/healthinfo/a-z/files/wnv_Repellent.pdf but I will break it down:
Everyone:
•Can use insect repellent that contains Soybean Oil (the 2% solution lasts about 3 hours)

Children Under 6 Months of Age:
•Should not use DEET

Children 6 Months to 2 Years Old:
•Can use insect repellent with up to 10% DEET (check the bottle for concentrations) once per day, each application will last about 3 hours

Children between 2 and 12 Years of Age:
•Can use insect repellent containing up to 10% DEET up to three times a day, each application will last about 3 hours

Children Under 3 Years of Age:
•Should NOT insect repellents with Lemon Eucalyptus Oil
•Should NOT insect repellents with Citronella Oil

Adults and Individuals 3 Years of Age and Older:
•Can use insect repellent with up to 30% Lemon Eucalyptus Oil, each application will last up to 5 hours for the 30% solution (2 hours for the 10% solution)
•Can use insect repellent with up to 15% Citronella Oil, each application will last up to 1 hours for the 15% solution (30 minutes for the 5% solution)

Adults and Individuals 12 Years Old and Older:
•Can use insect repellent containing up to 30% DEET (each application will last about 6 hours)

Please Note: At CD Whyte Ridge Pharmacy, we make natural citronella mosquito repellents for our clients. That’s because we don’t like mosquitoes either and we’re not all that fond of the chemical smell of DEET!

Wishing you the best of health and a mosquito-free summer,

Dennis Wong, Owner of CD Whyte Ridge, Consultant Pharmacist