Comparative Biology of Animal Coronaviruses: Lessons for SARS

New strains with altered tissue tropism can arise from existing strains through mutation. For example, the porcine respiratory coronavirus (PRCV) is a less virulent variant of TGEV and feline infectious peritonitis virus (FIPV) is the virulent variant of feline enteric coronavirus (FECoV).5,6 Alternatively, new strains may occur after recombination events such as the potential S gene recombinants between canine coronavirus (CCoV) and FECoV type 1 leading to a new FECoV serotype (type 2)6,7 or the acquisition of an influenza group C-like haemagglutinin (HE) by BCoV or its CoV ancestor.8 In addition, like SARS, new animal strains have emerged from unknown sources such as the porcine epidemic diarrhoea virus (PEDV) that first appeared in Europe and Asia between 1978 and the 1980s. It initially caused high diarrhoeal mortality in suckIntroduction