Invasive Rodents as a Source of Astroviruses in Réunion Harriers (Circus maillardi)

Astroviruses (AstVs) are RNA viruses infecting a wide range of vertebrates, with increasing evidence of cross-species transmission. We investigated the presence of AstVs in the Réunion Harrier (Circus maillardi), a critically endangered raptor endemic to Réunion Island. Cloacal and oropharyngeal swabs were collected from 133 individuals sampled between 2015 and 2024. Reverse transcription and seminested conventional PCR was used to detect the AstV RNA-dependent RNA polymerase gene. In total, 5.3±3.8% of birds tested positive, with no significant association with age, sex, or sampling method. All positive samples were obtained from wild-caught individuals except one detected from a bird at the care center. Phylogenetic analysis revealed that all sequences were genetically related to rodent-associated AstVs previously detected on Réunion Island and in Madagascar, and they did not cluster with avian lineages. These findings are consistent with previous results in the endemic Réunion free-tailed bat (Mormopterus francoismoutoui). For Réunion Harriers, they further suggest recurrent exposure to nonnative rodent-associated viruses through predation. The pathogenic potential of such viruses in wildlife remains unknown, but it could be amplified in insular species lacking prior exposure or coevolutionary history. Our results support the need to better integrate wildlife disease surveillance into island conservation strategies.