Engineering a mouse-adapted SADS-CoV and establishing a neonatal mouse model to study its infection

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is an emerging bat-origin alphacoronavirus causing severe disease in neonatal piglets, with significant economic losses to the swine industry as a consequence. The virus exhibits a broad species tropism, infecting cells derived from pigs, humans and mice, highlighting its potential for cross-species transmission. Due to drawbacks associated with the use of young piglets, there is a need for an appropriate small animal model to study SADS-CoV biology. Here we established a mouse infection model based on a murinized mutant of the virus, mSADS-CoV, in which the ectodomain of the viral spike protein was replaced by that of the murine coronavirus mouse hepatitis virus (MHV). This chimeric virus, generated through targeted RNA recombination, replicated efficiently in murine cell cultures and exhibited an age-dependent infection in neonatal mice that was lethal in 2-day-old BALB/c mice affecting various organs, notably the intestine. We validated our infection model by successfully verifying the efficacy of the RNA-dependent RNA polymerase inhibitor remdesivir (RDV). The model will serve as a valuable tool for studying SADS-CoV pathogenesis and for elucidating the roles of host factors in viral replication as well as for preclinical evaluation of vaccine candidates and antiviral compounds targeting the viral replication machinery.