Continued Evidence of Decline in the Enzootic Activity of Western Equine Encephalitis Virus in Colorado.

This research investigates the decline in the activity of Western Equine Encephalitis Virus (WEEV) in Colorado, using mosquito sampling in 2016 as evidence for the absence of WEEV infections among mosquitoes in Northern Colorado.

Study Objective and Method

• The primary objective of the research was to examine pools of Culex tarsalis mosquitoes from Weld County, Colorado, for traces of WEEV infection.
• WEEV was historically prevalent and commonly isolated from mosquitoes in Colorado but hasn’t been reported since the early 1990s. Thus, the research aimed to test whether WEEV is still circulating within the mosquito population.
• Over 7,000 mosquitoes were sampled and tested for WEEV RNA as part of the study.

Findings and Possible Explanations

• The study found that none of the mosquitoes tested positive for WEEV RNA, pointing to the continued evidence of a decline in the enzootic activity of the virus in Colorado.
• Several explanations are offered for these findings: either WEEV was not circulating in Northern Colorado at all, it was so rare that more extensive sampling would have been required to detect it, or it was disjointedly distributed across space and time, and hence, wasn’t present in the sampled region in 2016.

Implications and Future Considerations

• Despite reporting a null incidence of WEEV, the study emphasizes the importance of continuous screening for WEEV viral RNA in mosquito vectors. This would aid in predicting and preventing future outbreaks of WEEV.
• The researchers suggest that the study findings may imply a drastic decrease or even potential total elimination of WEEV in Colorado, but they caution against jumping to this conclusion without more comprehensive and diverse sampling efforts.