First evidence that an emerging mammalian alphacoronavirus is able to infect an avian species

A novel swine enteric alphacoronavirus, swine acute diarrhoea syndrome coronavirus (SADS-CoV), related to Rhinolophus bat CoV HKU2 in the subgenus Rhinacovirus emerged in southern China in 2017, causing diarrhoea in newborn piglets, and critical questions remain about the pathogenicity, cross-species transmission and potential animal reservoirs. Our laboratory's previous research has shown that SADS-CoV can replicate in various cell types from different species, including chickens. Here, we systematically explore the susceptibility of chickens to a cell-adapted SADS-CoV strain both in vitro and in vivo. First, evidence of SADS-CoV replication in primary chicken cells, including cytopathic effects, immunofluorescence staining, growth curves and structural protein expression, was proven. Furthermore, we observed that SADS-CoV replicated in chicken embryos without causing gross lesions and that experimental infection of chicks resulted in mild respiratory symptoms. More importantly, SADS-CoV shedding and viral distribution in the lungs, spleens, small intestines and large intestines of infected chickens were confirmed by quantitative reverse transcription polymerase chain reaction and immunohistochemistry. The genomic sequence of the original SADS-CoV from the pig source sample in 2017 was determined to have nine nucleotide differences compared to the cell-adapted strain used; among these were three nonsynonymous mutations in the spike gene. These results collectively demonstrate that chickens are susceptible to SADS-CoV infection, suggesting that they are a potential animal reservoir. To our knowledge, this study provides the first experimental evidence of cross-species infection in which a mammalian alphacoronavirus is able to infect an avian species.