Co-circulation dynamics and persistence of newly introduced clades of 2012 outbreak associated West Nile Virus in Texas, 2012-2015

The second largest outbreak of West Nile encephalitis and West Nile fever ever recorded occurred in the United States (U.S) in the summer of 2012. The outbreak was related to the widespread circulation of closely related clades, or groups, of West Nile virus (WNV) into multiple states where they were not previously found. Whether the invading 2012 strains were able to circulate and overwinter in states with their own endemic population of WNV is unknown and the effect of viral genetics on adaptation and persistence in a new ecological niche is unclear. In this study, we sequenced 70 mosquito isolates from multiple counties throughout Texas in 2012-2015. We identified isolates representative of previously described 2012 WNV groups (Groups 8-10) and discovered a novel group which we called Group 11. Although we identified isolates representative of WNV endemic (2/70) to Texas, most isolates (68/70) were related to the invading 2012 strains, and of these Group 10 (45/68) was predominant. We also observed differences among the 2012 WNV groups correlating to their genotype. Group 10 WNV in Texas, which carry two putative positively selected variants, had limited introductions into Texas, wide circulation, and strong evidence of continued persistence perhaps indicative of overwintering. In contrast, Groups 8 and 11, without positively selected variants, had multiple introductions into Texas, limited circulation, and limited persistence. Lastly, we identified a potential transmission source in New York for incoming Group 8 WNV into Texas. Altogether our study suggests that mutations in the WNV genome may influence the range and dynamics of WNV circulation, and the ability of different strains to persist in new ecological niches.