Thus, zoonotic CoVs pose a major threat to human health, with different animals serving as natural reservoirs or intermediate hosts to CoVs transmittable to humans [9, 10]. However, the potential threat represented by cats and dogs or their CoVs has been sparsely studied.
Different genotypes (I, II) of canine CoVs (CCoVs) of Alphacoronavirus 1 species cause moderate-to-severe enteric disease in dogs [11]. CCoV-II circulation has been confirmed in dogs since 1971, and CCoV-I was discovered about 3 decades later [12, 13]. Transmissible gastroenteritis virus (TGEV), CCoV-II, and feline CoV (FCoV) II have reportedly originated from CCoV-I and FCoV-I through gene loss and recombination [14]. Similarly to FCoVs, CCoV-I strains do not grow or grow poorly in cell culture and their cellular receptor is unknown, while CCoV-II strains grow readily in culture using aminopeptidase N as a cellular receptor [15]. This emphasizes the complex evolution of CCoVs/Alphacoronavirus 1 species and their ability to infect different hosts, inducing variable clinical disease. It has been demonstrated that another CoV, using aminopeptidase N as a cellular receptor, porcine deltacoronavirus, can infect cells of unusually broad species origin, including human and chicken [16].