Weekly West Nile & Culex Reports

The hard frosts of the last two nights throughout southern and central Saskatchewan have effectively ended the West Nile season for 2011.

Cooler night-time temperatures continue to reduce the WNv risk.

Declining numbers of Culex tarsalis, and a return to cooler night-time temperatures will reduce the WNv risk from early and mid August levels.

West Nile risk still present but declining.

The risk for West Nile remains at relatively low levels compared to other years throughout all of southern Saskatchewan. However, people are advised to avoid getting bitten by mosquitoes, particularly in the evening and through the night when Culex tarsalis is most active.

First positive Culex tarsalis mosquitoes reported in Saskatchewan.

Culex tarsalis numbers are peaking in southern areas and Culex tarsalis is becoming the dominant mosquito. Numbers and the level of risk are higher in the flood-affected areas of south east and south central Saskatchewan.

This is the time of year when peak West Nile virus transmission occurs and conditions have been optimal for transmission and spread of the virus if it is present in the environment. There has been one (1) human case reported from North Dakota and one (1) from South Dakota.

No positive mosquito pools reported for week 28 but the proportion of Culex tarsalis of the total mosquitoes is increasing. This trend of rising numbers and percentages will continue over the next two weeks.

Although there have been no positive mosquitoes, birds, horses or humans reported to date, conditions are particularly conducive for mosquito biting and egg-laying activity.

Warmer temperatures and drier conditions expected this week will advance Culex tarsalis mosquito development throughout all of southern Saskatchewan.

Risk to people remains low, with no positive mosquito pools reported in Saskatchewan or adjacent provinces and states. Larger number of mosquitoes are expected in July.