Insect-specific Alphamesonivirus-1 () in Lymph Node and Lung Tissues from Two Horses with Acute Respiratory Syndrome

Importance: Alphamesoniviruses, members of the family are considered insect-specific RNA viruses with no known association with vertebrate hosts. Herein, we report the identification of Alphamesonivirus-1 in mammals. Using detailed molecular and histological analyses, we identified Alphamesonivirus-1 in lung and lymph node tissues of two horses that presented with an acute respiratory syndrome and that was phylogenetically related to virus sequences found in local mosquitoes. Hence, Alphamesoniviruses may possess a broader host range than previously believed, prompting the investigation of their possible role in mammalian disease. This work highlights the need for increased surveillance of atypical viruses in association with unexplained respiratory illness, including those commonly assumed to be insect-specific, and may have implications for epizootic disease emergence.