Seventeen more Manitobans have been diagnosed with West Nile virus, bringing the total number of human cases reported in the province to 42 this year.

Four of the 42 cases were identified through routine screening by Canadian Blood Services, the rest through clinical testing.

Most people who contract West Nile virus show no symptoms. Of those who do, most experience flu-like symptoms such as fever, headaches, fatigue and body aches.

The virus can cause the more serious West Nile neurological syndrome, which can result in weakness, paralysis, confusion, coma or — in rare cases — death.

The province has released statistics on the severity of the illness in only the first 25 cases diagnosed this year. Of those, only one — an out-of-province patient — showed symptoms of the neurological syndrome.

The highest risk of human exposure to West Nile virus in Manitoba occurs in the last three weeks of July and the first three weeks of August. In 2006, there were 50 reported cases of the virus in people in the province.

People can reduce their risk of exposure to the virus by spending less time outdoors during peak mosquito hours and by wearing mosquito repellent and light-coloured, loose-fitting clothing.

More fogging in Winnipeg, other communities

To control the population of adult Culex tarsalis mosquitoes — the type most likely to spread the virus — the province has issued more orders under the Environment Act to fog with malathion.

A new order was issued Thursday for the town of Carberry, and orders previously issued will continue in Boissevain, Brandon, Carman, Deloraine, West St. Paul, Winkler and parts of Winnipeg.

Adult mosquito control will be undertaken at Sioux Valley First Nation, based on a recommendation from the chief medical officer of health to the First Nations and Inuit Health Program of Health Canada.

Fogging trucks will hit Winnipeg's streets Friday night, targeting the east and north-central parts 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.

The City of Winnipeg suspended its fogging program for nuisance mosquitoes last week, citing the low population of the blood-suckers in the city.

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.

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