Manitoba's first human case of West Nile virus infection

The first human case of West Nile virus infection this year has been identified in Manitoba. The individual, a Winnipeg resident in his sixties, is currently in hospital. The individual has been reported to Health Canada as a probable case of West Nile neurological syndrome.

Although a resident of Winnipeg, the individual is known to also have spent time in the area of the Rural Municipality of St. Clements during the period of probable exposure.

Usually, people infected by West Nile virus have no symptoms and do not become ill. Of those who do become ill, most will develop West Nile fever, an illness with symptoms such as fever, headache, fatigue and body aches. Less frequently, the virus can cause more serious illness (West Nile neurological syndrome) including encephalitis, an inflammation of the brain.

Encephalitis can have serious complications. These complications may include weakness, paralysis, confusion, coma and death and are more likely to occur among older adults and people with chronic diseases and weakened immune systems.

There is no vaccine or specific treatment for West Nile virus. Milder symptoms of West Nile fever usually improve without medical care. Anyone experiencing severe symptoms (such as persistent high fever, muscle weakness, headache) should seek medical attention promptly for diagnosis and care.

Mosquito surveillance in southern Manitoba indicates that the activity of Culex tarsalis, the mosquito that carries West Nile virus, decreased in all regional health authorities during the week of Aug. 8 to 14.

The average trap counts for Culex tarsalis in regional health authorities gathered during the week of Aug. 8 to 14 are: Assiniboine, 17; Brandon, four; Central, two; Interlake, one; North Eastman, one; Parkland, eight; South Eastman, two; and Winnipeg, 32.

Infected mosquitoes have been found in the following communities: Winnipeg, Brandon, Souris, Deloraine, Killarney, Winkler, West St. Paul and East St. Paul. The infection rate of trapped mosquitoes remains low, usually less than one per 1,000 mosquitoes.

The risk of exposure to WNV in Manitoba increases as the number and activity of infected Culex tarsalis mosquitoes increase. The activity of Culex tarsalis as indicated by trap counts is affected by many factors including the number of mosquitoes in the area, temperature, humidity and wind speed. In 2003, the majority of the human cases were exposed during the first two weeks of August.

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