Emergence of pathogenic coronaviruses in cats by homologous recombination between feline and canine coronaviruses

Abstract

Type II feline coronavirus (FCoV) emerged via double recombination between type I FCoV and type II canine coronavirus (CCoV). In this study, two type I FCoVs, three type II FCoVs and ten type II CCoVs were genetically compared. The results showed that three Japanese type II FCoVs, M91-267, KUK-H/L and Tokyo/cat/130627, also emerged by homologous recombination between type I FCoV and type II CCoV and their parent viruses were genetically different from one another. In addition, the 3'-terminal recombination sites of M91-267, KUK-H/L and Tokyo/cat/130627 were different from one another within the genes encoding membrane and spike proteins, and the 5'-terminal recombination sites were also located at different regions of ORF1. These results indicate that at least three Japanese type II FCoVs emerged independently. Sera from a cat experimentally infected with type I FCoV was unable to neutralize type II CCoV infection, indicating that cats persistently infected with type I FCoV may be superinfected with type II CCoV. Our previous study reported that few Japanese cats have antibody against type II FCoV. All of these observations suggest that type II FCoV emerged inside the cat body and is unable to readily spread among cats, indicating that these recombination events for emergence of pathogenic coronaviruses occur frequently.

Figure 1. Schema of feline and canine coronaviruses.

(A) Schema of type II CCoV. Each ORF is indicated by squares. Arrowheads indicate location of primers for amplification of partial RdRp, partial S and full N genes. (B) Schema of type II CCoV fc1, type II FCoV M91-267, KUK-H/L and Tokyo/cat/130627, and type I FCoV C3663 and Yayoi. Blue boxes indicate ORFs originating from type II CCoV. Red boxes indicate ORFs originating from type I FCoV.

Figure 2. Phylogenetic trees using partial RdRp(A), partial S (B) and N (C) genes.

Type I FCoVs, type II FCoVs and type II CCoVs are shown in red, green and blue, respectively. Swine CoV (TGEV and PRCoV), ferret CoV (FRCoV) and human CoV (HCoV) are shown in black. GenBank accession numbers are shown in parentheses.

Figure 3. Simplot analysis of canine and feline coronaviruses.

Similarity between nucleotide sequences of 3′-region of genome of type II CCoV fc1, type I FCoV Black, and type II FCoVs KUK-H/L, M91-267 and Tokyo/cat/130627. Horizontal axis refers to nucleotide position of fc1. Upper region of the plot map shows ORF structure in type II CCoV fc1 and corresponds to nucleotide positions in the plot map. A similarity of 1.0 indicates 100% identity with the nucleotide sequence. Parameters for calculation were as follows: window size, 200 bp; and step size, 40 bp.

Figure 4. Alignment of M and 3′-terminal of S genes in canine and feline coronaviruses.

(A) Alignment of M genes of CCoV and FCoV strains. Two regions in squares are conserved regions among type II CCoV fc1, type II FCoVs M91-267, KUK-H/L and Tokyo/cat/130627 and type I FCoV C3663. (B) Alignment of 3′-terminal of S genes of CCoV and FCoV strains. Square indicates conserved region. Nucleotide sequences originating from type II CCoV and type I FCoV are shown in blue and red, respectively. Dots indicate the same sequences with type II CCoV fc1.

Figure 5. Hypothesis of emergence of type II FCoV.

Some cats persistently infected with type I FCoV are superinfected with type II CCoV which is excreted from dogs. Inside the cat body, type II FCoV emerges by homologous recombination and induces severe clinical disease, FIP. Diseased cats do not spread type II FCoV.