Ferret systemic coronavirus (FRSCV) infection is associated with an emerging, highly fatal disease of ferrets. Enhanced macrophage tropism and the resulting induction of pyogranulomatous lesions are shared with feline infectious peritonitis virus (FIPV) infection in cats, but are not features of ferret enteric coronavirus (FRECV) infection. Comparative sequence analysis of the distal one-third of the genomes of one FRSCV and one FRECV strain showed that these two ferret coronaviruses share >96% nucleotide sequence identities in the membrane (M), nucleocapsid (N) and non-structural protein genes (partial polymerase, open reading frames [ORFs] 3 and 7b). The envelope (E) protein gene showed a moderate nucleotide sequence similarity of 91.6%. In contrast, nucleotide and amino acid sequence similarities observed with the spike (S) protein were only 79.5 and 79.6%, respectively. Twenty-one amino acid differences within a 195-199-amino acid C-terminal portion of the S protein were conserved between 3 strains each of FRSCV and FRECV. Both systemic and enteric strains were found to carry a single ORF 3 gene with truncated proteins observed in two out of three FRSCV strains examined. The two enteric strains analyzed each contained an intact ORF 3 gene. Phylogenetically, FRSCV is more closely related to FRECV than to other group 1 coronaviruses.
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