Evidence for current circulation of an ancient West Nile virus strain (NY99) in Brazil.

INTRODUCTION In Brazil, West Nile virus (WNV) was first detected, in 2018, in horses with neurological disease. AIM We report the first case of WNV infection in a horse from Ceara state and the complete genome sequence of an isolate from Espirito Santo state. Both infections occurred in 2019. METHODS WNV was isolated from the tissues of a horse with neurological signs in Espirito Santo and sequenced by MiSeq. RESULTS Phylogenetic analysis revealed that the isolate belongs to lineage 1a, clustering with the NY99 strain, a strain that has not circulated in the USA since 2005. CONCLUSIONS Our findings reinforce the hypothesis that WNV has been silently circulating in Brazil for many years.