First identification of a single amino acid change in the spike protein region of feline coronavirus detected from a coronavirus-associated cutaneous nodule in a cat.

Case summary: A 32-month-old spayed female Singapura cat presented with a non-pruritic erythematous nodule on the upper lip. The cat also had multiple nodules in the liver but exhibited no other clinical signs consistent with classical feline infectious peritonitis (FIP), such as pleural effusion or ascites, uveitis or neurological symptoms. Histopathological and immunohistochemical analyses of the cutaneous nodule revealed pyogranulomatous dermatitis with intralesional macrophages laden with feline coronavirus (FCoV) antigen. Real-time reverse transcription (RT)-PCR of a cutaneous sample revealed a single nucleotide substitution in the spike protein gene of FCoV (mutation M1058L), which is consistent with an FCoV genotype commonly associated with FIP. The cat received a blood transfusion and supportive therapy, but the owner declined to continue the treatments owing to poor response. The cat was lost to follow-up 5 months after discharge.

Relevance and novel information: This report describes a case of a coronavirus-associated cutaneous nodule in which the evidence of amino acid changes in the spike protein gene identified by RT-PCR were consistent with an FCoV genotype commonly seen in cases of FIP. To the best of our knowledge, this is the first report of a case of cutaneous disease associated with the mutated FCoV that was confirmed by molecular diagnostic testing.