Mutations of 3c and spike protein genes correlate with the occurrence of feline infectious peritonitis.

•Sequence comparison of FIPV/FECV.•ORF3c genes of FIP animals heavily affected by nucleotide deletions/point mutations.•Genes encoding 3a, 3b, 7a and 7b displayed no mutations linked to the FCoV biotype.•Mutated 3c genes were found in ascites and faeces samples of FIP animals.•Slightly affected 3c genes were accompanied by mutations in S gene.