Insect-specific Alphamesonivirus-1 (Mesoniviridae) in lymph node and lung tissues from two horses with acute respiratory syndrome
Authors: Jurisic Lucija , Auerswald Heidi , Marcacci Maurilia , Di Giallonardo Francesca , Coetzee Laureen M. , Curini Valentina , Averaimo Daniela , Ortiz-Baez Ayda Susana , Cammà Cesare , Di Teodoro Giovanni , Richt Juergen A. , Holmes Edward C. , Lorusso Alessio 
Published: November 2024

ABSTRACTAs members of the RNA virus orderNidoviralesinclude those that infect hosts ranging from marine invertebrates to terrestrial mammals, understanding their emergence, host range and disease potential is of clear importance. TheMesoniviridaeare a recently documented family of viruses within theNidovirales. To date, mesoniviruses have only been associated with the infection of arthropods, particularly mosquitoes. Herein, we report the first detection of a mesonivirus – Alphamesonivirus-1 – in mammals. Specifically, we utilized genomic and histological techniques to identify the presence of Alphamesonivirus-1 in lung and lymph node tissues of two horses that succumbed to an acute respiratory syndrome. Notably, no other pathogens typically associated with respiratory disease in horses were detected in these samples. Counter to the previous contention that mesoniviruses only infect insects, our findings suggest a potentially broader host range and cross-species transmission of these viruses. The genome sequences of Alphamesonivirus-1 obtained from the two horses were closely related to those from a localCulexmosquito pool as well as an Alphamesonivirus-1 previously in identified Italy, suggestive of ongoing local transmission. The discovery of Alphamesonivirus-1 in tissues from diseased horses not only challenges current understandings of mesonivirus host range, but prompts further investigation into the role of insect-specific viruses in mammalian disease processes. Our results emphasize the importance of considering atypical pathogens in cases of unexplained animal deaths and suggest a potential zoonotic threat posed by previously overlooked viral families.IMPORTANCEAlphamesoniviruses, members of theMesoniviridaefamily, have long been considered insect-specific viruses with no known association with vertebrate hosts. Herein, we describe the first detection of Alphamesonivirus-1 in mammals, marking a significant expansion of the known host range for this newly described virus family. 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. Our findings indicate that Alphamesoniviruses may possess a broader host range than previously believed and could potentially induce severe disease in mammals. This unexpected host jump not only challenges existing knowledge on the ecology of mesoniviruses, but suggests that insect-specific viruses may pose a previously unrecognized health risk to vertebrates, including domesticated animals. These insights prompt the need for increased surveillance of atypical pathogens, especially in cases of unexplained respiratory illness, and may have implications for zoonotic disease emergence.