Understanding Human Coronavirus HCoV-NL63

Abdul-Rasool, Sahar; Fielding, Burtram C

Based on antigenicity, genome organization and sequence homology, coronaviruses are divided into three distinct groups [20] . Group 1 contains transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PDEV), feline infectious peritonitis virus (FIPV), canine coronavirus and HCoV-229E, among others. Group 2 contains mouse hepatitis virus (MHV), bovine coronavirus, haemagglutinating encephalomyelitis virus, HCoV-HKU1 and HCoV-OC43, to name a few, with Bat SARS-CoV and SARS-CoV considered distantly related Group 2b coronaviruses. Group 3 contains the avian coronaviruses [21] [22] [23] . Based on phylogenetic analysis, HCoV-NL63 belongs to the Group I coronaviruses [2, 24] . Interestingly, evidence of recombination during the evolution of HCoV-NL63 has been reported, and viral isolates have, in fact, a mosaic genome structure. The authors speculate that HCoV-NL63 diverged from a HCoV-229E ancestor in the past, followed by a separation into two distinct HCoV-NL63 lineages. These two lineages recombined during co-infection, giving rise to the two currently observed genotypic subgroups [24] [25] [26] [27] . In fact, recombination between different HCoV-NL63 isolates has been suggested, resulting in a mixture of clinical virus variants circulating in the human population [8, [27] [28] [29] [30] .