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

Osumi, Takafumi; Mitsui, Ikki; Leutenegger, Christian M; Okabe, Ryo; Ide, Kaori; Nishifuji, Koji

Based on these clinical and laboratory findings, we considered cutaneous cryptococcosis, chronic bacterial infection, dermatophytic pseudomycetoma, progressive dendritic cell histiocytosis, cutaneous lymphoma, eosinophilic granuloma complex, and FHV-or FIP-associated skin lesions as major differential diagnoses. To investigate these possibilities, a punch biopsy of the skin was performed under general anaesthesia, and the samples were subjected to histopathological and immunohistochemical analyses, culture and molecular diagnostic testing. Histopathological analysis revealed multifocal, severe pyogranulomatous dermatitis consisting of neutrophils, macrophages, epithelioid cells, and occasionally lymphocytes and plasma cells throughout the entire layer of the dermis (Figure 2 ). Immunohistochemical analysis with an anti-FCoV mouse monoclonal antibody (FIPV3-70; Bio-Rad Laboratories) 8 revealed intralesional macrophages laden with FCoV antigen (Figure 3 ). Periodic acid-Schiff staining, Grocott staining and Ziehl-Neelsen staining were negative for any infectious organisms (data not shown). Tissue culture results were negative for any bacteria, including acid-fast bacilli. No liver biopsy was performed because the owner declined.