Epidemiology of Deltacoronaviruses (δ-CoV) and Gammacoronaviruses (γ-CoV) in Wild Birds in the United States

Porcine deltacoronavirus (δ-CoV) is the object of extensive research in several countries including the United States. In contrast, the epidemiology of δ-CoVs in wild birds in the US is largely unknown. Our aim was to comparatively assess the prevalence of δ- and γ-CoVs in wild migratory terrestrial and aquatic birds in Arkansas, Illinois, Indiana, Maryland, Mississippi, Missouri, Ohio, Tennessee and Wisconsin. A total of 1236 cloacal/fecal swabs collected during the period 2015–2018 were tested for γ- and δ-CoVs using genus-specific reverse transcription-PCR assays. A total of 61 (4.99%) samples were γ-CoV positive, with up to 29 positive samples per state. In contrast, only 14 samples were positive for δ-CoV (1.14%) with only 1–4 originating from the same state. Thus, unlike previous reports from Asia, γ-CoVs are more prevalent than δ-CoVs in the US, suggesting that δ-CoVs may spread in birds with lower efficiency. This may indicate δ-CoV emerging status and incomplete adaptation to new host species limiting its spread. Phylogenetic analysis of the partial N gene revealed that the newly identified δ-CoV strains were most closely related to the HKU20 (wigeon) strain. Further studies are necessary to investigate the role of aquatic bird δ-CoVs in the epidemiology of δ-CoVs in swine and terrestrial birds.