Cross-species transmission of deltacoronavirus and the origin of porcine deltacoronavirus

Deltacoronavirus is the last identifiedCoronaviridaesubfamily genus. Differing from other coronavirus (CoV) genera, which mainly infect birds or mammals, deltacoronaviruses (delta-CoVs) reportedly infect both animal types. Recent studies show that a novel delta-CoV, porcine deltacoronavirus (PDCoV), can also infect calves and chickens with the potential to infect humans, raising the possibility of cross-species transmission of delta-CoVs. Here, we explored the deep phylogenetic history and cross-species transmission of delta-CoVs. Virus-host cophylogenetic analyses showed that delta-CoVs have undergone frequent host switches in birds, and sparrows may serve as the unappreciated hubs for avian to mammal transmission. Our molecular clock analyses show that PDCoV possibly originated in Southeast Asia in the 1990s and that the PDCoV cluster shares a common ancestor with Sparrow-CoV of around 1,810. Our findings contribute valuable insights into the diversification, evolution, and interspecies transmission of delta-CoVs and the origin of PDCoV, providing a model for exploring the relationships of delta-CoVs in birds and mammals.