Health officials in Manitoba ordered more chemical fogging to ward off the West Nile virus Thursday, in the wake of more than a dozen new cases of the mosquito-borne disease.

Sixteen more Manitobans have been diagnosed with West Nile virus, bringing the total number of human cases reported in the province to 58 this year.

Of these, six test results were identified by Canadian Blood Services routine screening, the rest through clinical testing.

One death from a West Nile virus infection in Manitoba has been reported this year. An 80-year-old man from the Assiniboine region died after he contracted the more severe type of virus, health officials said earlier this month.

Orders under the province's Environment Act were issued Thursday to fog with malathion to control adult mosquito populations in the town of Morris and the city of Portage la Prairie.

Fogging based on previously issued orders will continue in Altona, Brandon, Carberry, Morden, West St. Paul, Winkler and Winnipeg.

In Winnipeg, fogging trucks will hit the streets Friday night, targeting 14 locations in the north, east and west of the city.

The order from the province means fogging crews will ignore the 100-metre buffer zones the city allows around the homes of people who are opposed to the use of the pesticide.

Fogging takes place when the weather permits. Temperatures must be at least 13 C and there can be no significant wind or rain.

Health Canada approves the use of malathion in "ultra-low volume" applications to control the adult mosquito population. However, some critics question the insecticide's effectiveness in killing adult mosquitoes, and have raised concerns about possible health effects.

Provincial officials suggest people who wish to reduce their exposure to malathion:

• Close doors and windows.
• Turn off air conditioners.
• Bring in clothing and toys from the outdoors before fogging gets underway.

After fogging, household items left outdoors and homegrown produce should be washed before use.

Most people who are bitten by a mosquito infected with West Nile do not become ill. For those who do, the symptoms are usually mild. In some cases, the virus causes serious illness, and sometimes death.

Although the number of reported West Nile cases is higher this year than in previous years at this point in the season, officials have said there is no need to panic, and advised Manitobans to take precautions by covering up, using bug sprays and getting rid of standing water where mosquitoes breed.