Figure. A) Phylogenetic relationships of feline coronaviruses (FCoVs) detected in feces of healthy cats and in organs/ascites of cats with feline infectious peritonitis. Alignment of the matrix (M) gene sequences was used to generate a rooted neighbor-joining tree with the M gene sequence of canine coronavirus strain NJ17 (Genbank accession no. AY704917) as outgroup. Bootstrap confidence values (percentages of 1,000 replicates) are indicated at the relevant branching points. Branch lengths are drawn to scale; scale bar indicates 0.02 nucleotide substitutions per site. Viruses detected in cattery animals are indicated by a cattery designation after the virus identification number. B) Alignment of amino acid sequences of partial M proteins of the FCoVs from panel A, as compared with a feline infectious peritonitis virus (FIPV) reference sequence (top line) published by Brown et al. (9) (GenBank accession no. EU664166), and with 8 American FCoV sequences (bottom) published by Pedersen et al. (8). The 5 aa residues at positions 108, 120, 138, 163, and 199, suggested by Brown et al. (9) as potential diagnostic sites, are boxed.