West Nile Virus and Culex tarsalis (July 11, 2019; Wk 14)

West Nile Virus Risk –  In 2018, there were 426 human clinical cases of West Nile virus (WNV) in Canada (Fig. 1). 

Figure 1. Geographic distribution of WNV human clinical cases and asymptomatic infections in Canada, 2018.
Image has not been reproduced in affiliation with, or with the endorsement of the Government of Canada and was retrieved (11Jul2019).  Access the full map at https://www.canada.ca/en/public-health/services/publications/diseases-conditions/west-nile-virus-surveillance/2018/november-11-december-15-week-46-50.html

Health Canada posts information related to West Nile Virus in Canada.  Health Canada also tracks WNV through human, mosquito, bird and horse surveillance.  Link here to access the most current weekly update (June 29, 2019). The screenshot below was retrieved 11Jul2019 as reference but access that information here.

The Canadian Wildlife Health Cooperative compiles and posts information related to their disease surveillance for West Nile Virus in birds.  Take note of the provincial distribution of positive WNV birds in 2018 (table posted below as reference).

The following is offered to predict when Culex tarsalis will begin to fly (Fig. 2) across the Canadian prairies. Protect yourself by wearing DEET!  The regions most advanced in degree-day accumulations for Culex tarsalis, the vector for West Nile Virus, are shown in the map below.  Areas highlighted lime green in the map below (Fig. 2) are on the verge of approaching sufficient heat accumulation for mosquitoes to emerge soon.  

Figure 2. Predicted development of Culex tarsalis, across the Canadian prairies (as of July 7, 2019).

Once the adults emerge, the following map demonstrates how quickly a Culex tarsalis mosquito carrying WNV can become fully infective (i.e., when it has accumulated 109 base 14.3° degree days) - as quickly as 20-22 days, given the current environmental conditions in the highlighted areas of the map below (Figure 3).