July 15, 2011
West Nile Virus Update #1
While the cool spring has led to a slow start for Culex tarsalis mosquitoes, warm temperatures will accelerate mosquito development and the risk of exposure to West Nile virus (WNV).
The Office of the Chief Provincial Public Health Officer reminds Manitobans to prepare for summer mosquitoes by reducing standing water around the home, setting up screen tents to enjoy the outdoors, particularly between dusk and dawn, and repairing window and door screens. Personal protective measures, such as using an appropriate repellent, will help to reduce mosquito bites.
At this time, the risk of exposure to West Nile virus-infected mosquitoes is low and analysis of the adult mosquitoes trapped for the week of July 3 show low numbers of Culex tarsalis mosquitoes. None of the mosquitoes collected to date have tested positive for West Nile virus.
Preliminary trap information for the week of July 10 indicates the numbers of Culex tarsalis mosquitoes have increased in some communities and it is possible that infected mosquitoes are present in southern Manitoba. The risk of being bitten by a mosquito carrying West Nile virus is predicted to increase in the coming weeks.
West Nile virus can cause severe illness such as encephalitis, but more commonly causes a milder illness including fever, headache, fatigue, body aches and rash. About 80 per cent of people will have no symptoms when they become infected with the virus.
The number of WNV cases varies each year, depending on environmental factors, particularly temperature. Last year, for the first time since 2002, no human cases of WNV were identified in Manitoba. However, in 2007, the year with the largest outbreak, 587 human cases were reported with 72 severe cases (West Nile virus neurological syndrome) and four deaths associated with WNV.
Weekly average trap counts of Culex tarsalis by regional health authority are available on the province’s West Nile virus website at www.gov.mb.ca/health/wnv/.
Manitobans can reduce mosquitoes around their home by reducing standing water. To prevent the development of Culex tarsalis mosquitoes, homeowners can:
- clean eavestroughs and regularly empty bird baths and other items that might collect water,
- ensure rain barrels are covered with mosquito screening or are tightly sealed around the downspout,
- clear yards of old tires or other items that collect water, and
- improve landscaping to prevent standing water around the home.
Manitobans can reduce the risk of mosquito bites by:
- reducing the amount of time spent outdoors during peak mosquito hours between dusk and dawn;
- using appropriate mosquito repellent;
- wearing light-coloured, loose-fitting clothing; and
- maintaining door and window screens so they fit tightly and are free of holes.
Information on the risk of West Nile virus will be provided throughout the summer. Manitobans can also check the WNV website regularly for up-to-date data.
For more information about West Nile virus, contact Health Links–Info Santé at 788-8200 or 1‑888‑315-9257 (toll-free). Trap count information is updated weekly and available on the Manitoba Health website at www.gov.mb.ca/health/wnv/.
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