July 21, 2004
Current mosquito surveillance is indicating large increases in the numbers of Culex tarsalis mosquitoes—the mosquitoes most likely to carry West Nile virus—in southern Manitoba.
Average one-night Culex tarsalis U.S. Centers for Disease Control (CDC) trap counts by regional health authority for the week of July 11 were:
-Assiniboine RHA – 93
-Brandon RHA – 35
-RHA Central – 30
-Interlake RHA - 1
-North Eastman RHA – 5
-Parkland RHA – 5
-South Eastman RHA – 29
-Winnipeg RHA - 192
Mosquito surveillance within the City of Winnipeg and the Town of Deloraine in southwestern Manitoba during the week of July 11 showed the highest average counts of adult Culex tarsalis mosquitoes.
In Winnipeg, the average one-night Culex tarsalis CDC trap count was 192. In Deloraine, the average one-night Culex tarsalis CDC trap count was 561.
Several communities, including Winnipeg and Deloraine, are undertaking West Nile virus-related larviciding activities through a cost-sharing program with the province’s West Nile virus program.
Testing of the mosquitoes for WNV is ongoing. It is anticipated that WNV will soon be identified in Culex tarsalis mosquito samples.
At this time, there are no recommendations for adulticiding for West Nile virus.
The situation is being closely monitored for any change in mosquito patterns and infection rates. The public will be notified if adult mosquito control activities are planned.
Last year, the first positive mosquito sample was identified on July 4, 2003, and analysis of the human case data from 2003 indicated that initial human cases were exposed in mid-July.
As we enter the later part of July, and with the identification of increasing numbers of Culex tarsalis mosquitoes, the risk of exposure to WNV in Manitoba is expected to increase.
To reduce the risk of West Nile virus infection, Manitobans can protect themselves against mosquito bites. This includes:
- wearing light-coloured, loose-fitting clothing, long-sleeved tops and long pants;
- using mosquito repellent containing DEET;
- reducing the amount of time spent outdoors during peak mosquito hours between dusk and dawn; and
- keeping mosquitoes out of indoor spaces by checking door and window screens to make sure they fit tightly and are free of holes.
Public awareness for personal protection and reduction of water sources are being enhanced through the website, a West Nile virus pamphlet, and radio and television advertising over the next few weeks.
Manitobans can reduce the number of mosquitoes by emptying standing water that may collect in backyards, old tires, children's toys, pet bowls, wading pools or stagnant ponds, eaves troughs, under flower pots, etc.
As of July 20, crows have tested positive for West Nile virus in the following areas: Winnipeg (north, west and east), the Parkland Regional Health Authority and the Assiniboine Regional Health Authority.
Manitobans can continue to help detect the arrival of West Nile virus in their area by reporting dead crows, blue jays, magpies or ravens to Health Links-Info Santé at 788-8200 in Winnipeg (outside of Winnipeg toll-free 1-888-315-9257) in the following areas: South Winnipeg, Brandon RHA, RHA Central, Interlake RHA, North Eastman RHA, South Eastman RHA, NOR-Man RHA, Burntwood RHA and Churchill RHA.
West Nile virus identified in birds from the crow family provides an early indication of West Nile virus in an area. It is likely that birds will be identified soon in other regional health authorities in southern Manitoba. Once testing has demonstrated the presence of WNV in a specific area, no further birds from that area are required for testing.
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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