September 02, 2004

·         Based on mosquito surveillance, the time of year and the life cycle of the Culex tarsalis mosquito, the current risk of becoming infected with West Nile virus in Manitoba is considered low and is expected to continue to decrease.

·         While it is anticipated that additional human cases of WNV will be identified in Manitoba this season, it is likely that exposure to the virus in most newly identified cases will likely have occurred in late July or early August.

·         Current mosquito surveillance in southern Manitoba indicates that the activity of Culex tarsalis, the main mosquito species that carries West Nile virus in Manitoba, remained low in all regional health authorities during the week of Aug. 22 to 28.

·         The average trap counts for Culex tarsalis in regional health authorities gathered during the week of Aug. 22 to 28 were: Assiniboine, one; Brandon, one; Central, three; Interlake, none; North Eastman, none; Parkland, none; South Eastman, one; and Winnipeg, one.

·         There were no WNV infected mosquitoes identified during the week of Aug. 22 to 28. Earlier this summer, WNV infected mosquitoes were found in the following communities: Brandon, Souris, Deloraine, Killarney, Winkler, Winnipeg, West St. Paul and East St. Paul.

·         At this time of year and during the rest of this season, it is expected that newly hatched Culex tarsalis mosquitoes will not blood feed. A few older Culex tarsalis mosquitoes may be infected with WNV and still pose risk of WNV, particularly in warmer weather. Consider using personal protection at any time when mosquito activity is noticed, especially for people over the age of 50 or with chronic medical conditions or weakened immune systems.

·         It is anticipated that the numbers of nuisance mosquitoes will increase over the next few weeks in Manitoba as a result of recent rains.

·         Two human cases of West Nile virus infection have been identified so far this year in Manitoba. One individual has been reported as a probable case of West Nile neurological syndrome while the other individual has been determined to be a probable case of West Nile fever.

·         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.

·         Birds from the NOR-MAN Regional Health Authority, the Burntwood Regional Health Authority and the Churchill Regional Health Authority will continue to be considered for WNV testing to establish the presence of WNV in those areas. No further birds are required for testing from southern Manitoba.

·         Public information about West Nile virus is available by calling Health Links-Info Santé at 788-8200 in Winnipeg or toll-free at 1-888-315-9257. Additional information is available on the Manitoba Health website at http://www.gov.mb.ca/health/wnv, which is updated with surveillance data weekly.

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