Warm weather causes mosquito increase

B.C.’s cool spring season temperatures have helped keep the mosquito population in check.

  • Aug. 5, 2011 10:00 a.m.

B.C.’s cool spring season temperatures have helped keep the mosquito population in check.

However, with temperatures on the rise, the BC Centre for Disease Control (BCCDC) is warning that the mosquito population is increasing, and some of these mosquitoes may carry West Nile virus (WNV).

Increases have been seen particularly in the Okanagan and the Fraser Valley, and the public should to take appropriate precautions to prevent mosquito bites.

WNV is transmitted from birds to people through the bite of an infected mosquito. The BCCDC, an agency of the Provincial Health Services Authority, routinely monitors for WNV throughout the province.

To date this year, there have been no positive test results from human, animal, or mosquito samplings in B.C., Oregon, or Washington State. However, as the mosquito population increases, so does the risk.

One individual in Ontario who had been travelling out of the country is the only Canadian known to have tested positive so far this year.

“However, individuals still need to be vigilant and take precautions to avoid being bit,” says Dr. Bonnie Henry, physician epidemiologist with the BCCDC. “Simple things such as using repellents outdoors, particularly in the evening and early morning when mosquitoes are most active, is a good protective measure.”

Eighty per cent of people who are bitten by a mosquito and infected with WNV will not have any symptoms. About 20 per cent of infected people may develop some symptoms, including fever, fatigue, headaches and swollen lymph glands. In rare cases (one in 150), WNV can cause severe illness, such as inflammation in or around the brain (encephalitis or meningitis), or polio-like paralysis, that can occasionally result in death.

There are many things that British Columbians should do to reduce their risk of being bitten by mosquitoes that may carry WNV, including:

• Remove any standing water outdoors from empty containers (e.g. flower pots, wheel barrows, old tires, barrels, tin cans, and even bottle tops) at least twice a week

• Drill holes in used containers, so water can’t collect

• Change water in bird baths twice weekly

• Immediately remove water that collects on swimming pool covers, and ensure that the pool’s pump is circulating

• Clear leaves and twigs from eaves and storm gutters throughout the summer into early fall, so water doesn’t pool or collect

• Check flat roofs frequently for standing water — you can apply environmentally safe mosquito larvicides available at garden centres to standing water that cannot be drained

• Ensure that drains and drainage ditches are not clogged

• Stop mosquitoes from entering your home or other premises (check windows and door screens for holes or tears, and make sure they fit snugly into their frames)

• Take personal protective measures outdoors, such as wearing long sleeves and pants (weather permitting) with light colours and a tight weave, as well as a hat — especially at dawn and dusk when mosquitoes that can carry WNV are most active

• Use federally registered mosquito repellents such as those containing DEET and PMD (also known as lemon-eucalyptus oil), strictly according to directions. Re-apply repellents as often as necessary.