August 24, 2006

As of the end of the day yesterday, test results indicated eight additional human cases of West Nile virus had been identified in Manitoba during the previous week, bringing the total number of Manitobans who have tested positive for West Nile virus this year to 25.

Of the 25 Manitobans who have tested positive this year, five have been classified as cases of West Nile neurological syndrome, eight have been classified as cases of West Nile non-neurological syndrome and one has been classified as asymptomatic or showing no symptoms. The rest are currently under investigation to determine if they meet the criteria for cases of West Nile virus.

Additional information on these cases, including age, gender, regional health authority of residence and likeliest area of exposure, will be provided on the website when it becomes available at http://www.gov.mb.ca/health/wnv.

Even though mosquito activity may appear to be low, the risk of exposure to West Nile virus this summer has not yet ended. Mosquito trap data shows that a high proportion of active mosquitoes are Culex tarsalis and a significant number of those are infected with West Nile virus. Therefore, to reduce the risk of West Nile virus, Manitobans are still advised to take personal protective precautions against mosquitoes in both urban and rural areas, especially if the warm weather continues. As daytime and evening temperatures become cooler, Culex tarsalis mosquitoes may become more active during the day and early evening as well as between dusk and dawn.

Manitobans can reduce the risk of mosquito bites by:

• reducing the amount of time spent outdoors during peak mosquito hours;

• using appropriate mosquito repellent;

• wearing light-coloured, loose-fitting clothing; and

• making sure doors and window screens fit tightly and are free of holes.

Adult mosquito trap information from the week of Aug. 13 indicates the numbers of Culex tarsalis mosquitoes in southern Manitoba generally decreased compared to the numbers from the week of Aug. 6.

Preliminary trap information from the week of Aug. 20 indicates the Culex tarsalis numbers in many southern Manitoba communities continue to drop compared to the numbers from the week of Aug. 13, with most communities showing a reduction in weekly average counts.

This year, positive mosquito samples have been found in 21 Manitoba communities: Steinbach, Carman, Selkirk, Boissevain, Carberry, Portage la Prairie, Gimli, Niverville, St. Andrews, Beausejour, Headingley, West St. Paul, Winnipeg, Brandon, Deloraine, East St. Paul, Stony Mountain, Oakbank, Sioux Valley First Nation, Winkler and Altona. The risk of West Nile virus, however, exists throughout all of southern Manitoba and is not limited to the communities listed. West Nile virus has been identified in this or previous years within the boundaries of all regional health authorities except for NOR-MAN, Burntwood and Churchill.

Given the time of season and current data, adult mosquito control fogging is no longer considered to be an effective option. However, Manitobans should continue to reduce the number of Culex tarsalis mosquitoes around their homes by reducing standing water. This includes:

• regularly cleaning and emptying eavestroughs, bird baths and other items that might collect water;

• ensuring rain barrels are covered with mosquito screening or are tightly sealed around the downspout; and

• making sure yards are clear of old tires or other debris that collect water.

Weekly average trap counts of Culex tarsalis by regional health authority are available on the province’s West Nile virus website at http://www.gov.mb.ca/health/wnv.

For more information, visit the website or call Health Links/Info Santé at 1‑888‑315‑9257 or 788-8200 in Winnipeg.

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