Potential evolutionary influences on the reduction in enzootic circulation and human incidence of Western equine encephalitis

Western equine encephalitis virus (WEEV), an arbovirus in the family Togaviridae genus Alphavirus, has caused several epidemics that have resulted in the deaths of thousands of humans and hundreds of thousands of equids over the past century. Interestingly, reported WEEV infection has decreased precipitously over the past fifty years, with the most recent human case being reported in 1998. Using phylogenetic techniques we constructed a comprehensive evolutionary profile of the virus throughout the 20th and early 21st centuries, elucidated a constriction in genetic diversity, and discovered the presence of several mutations that could result in decreased fitness. Furthermore, these mutations are being tested in order to clarify their phenotypic effects on host and vector fitness.