An update on canine coronaviruses: viral evolution and pathobiology

Abstract

The emergence of human severe acute respiratory syndrome incited renewed interest in animal coronaviruses (CoVs) as potential agents of direct and indirect zoonoses. The reinforced epidemiological surveillance on CoVs has led to the identification of new viruses, genotypes, pathotypes and host variants in animals and humans. In dogs, a CoV associated with mild enteritis, canine coronavirus (CCoV), has been known since 1970s. CoV strains with different biological and genetic properties with respect to classical CCoV strains have been identified in dogs in the last few years, leading to a full reconsideration of the CoV-induced canine diseases. The genetic evolution of dog CoVs is paradigmatic of how CoVs evolve through accumulation of point mutations, insertions or deletions in the viral genome, that led to the emergence of new genotypes (CCoV type I), biotypes (pantropic CCoV) and host variants (canine respiratory coronavirus). This paper is a review of the current literature on the recent genetic evolution of CCoV and emergence of new CoVs in the dog. The significances of the newly acquired information for the canine health status and prophylaxis programmes are also discussed.

Fig. 1

Phylogenetic relationship of the S proteins of animal and human coronaviruses. The tree was generated by the neighbor-joining method in the Mega3 program (Kumar et al., 2004). For phylogenetic tree construction, the following CoV strains were used (GenBank accession numbers are reported in parentheses): group 1: canine coronavirus type II (CCoVII) Insavc1 (D13096), CCoVII-BGF10 (AY342160), CCoVII-CB/05 (DQ112226), canine coronavirus type I (CCoVI) Elmo/02 (AY307020), CCoVI-23/03 (AY307021), feline coronavirus type II (FCoVII) 79-1146 (NC_007025), FCoVII-79-1683 (X80799), feline coronavirus type I (FCoVI) KU-2 (D32044), FCoVI-Black (AB088223), FCoVI-UCD1 (AB088222), transmissible gastroenteritis virus (TGEV) Purdue (NC_002306), Chinese ferret badger coronavirus (CFBCoV) CFB/GD/DM95/03 (EF192156), human coronavirus (HCoV) NL63 (NC_005831); group 2: human severe acute respiratory syndrome coronavirus (SARS-CoV) Tor2 (NC 004718), bovine coronavirus (BCoV) Mebus (U00735), giraffe coronavirus (GiCoV) US/OH3/2003 (EF424623), alpaca coronavirus (ACoV) (DQ915164), sable antelope coronavirus (SACoV) US/OH1/2003 (EF424621), bubaline coronavirus (BuCoV) 179/07-11 (EU019216), canine respiratory coronavirus (CRCoV) 4182 (DQ682406), HCoV-OC43 ATCC VR-759 (NC_005147), human enteric coronavirus (HECoV) 4408 (L07748), porcine haemagglutinating encephalomyelitis virus (PHEV) VW572 (DQ011855), mouse hepatitis virus (MHV) A59 (AY700211), rat sialodacryoadenitis virus (SDAV) 681 (AF207551), HCoV-HKU1 (NC_006577), equine coronavirus (ECoV) NC99 (NC 010327); group 3: avian infectious bronchitis virus (IBV) Beaudette (NP 040831); turkey coronavirus (TCoV) G1 (AY342357). Coronaviruses of dogs are grey shaded. A statistical support was provided by bootstrapping over 1000 replicates. The scale bar indicates the estimated numbers of amino acid substitutions per site.

Fig. 2

Schematic representation of the genomes of CCoVs and FCoVs depicting the genetic differences among the CCoV genotypes/biotypes. Genes encoding for structural and non-structural proteins are shown in grey and white, respectively. ORF sizes are not drawn to scale. The arrows indicate the transcription regulating sequences preceding each CoV gene. The length in amino acids of the nsp 3b of strains BGF10 and CB/05 and the 38-nt deletion in ORF3b of strain CB/05 are reported.