Evaluation of Granulomatous and Vascular Lesions in Feline Infectious Peritonitis

Feline Infectious Peritonitis (FIP) is a fatal systemic viral disease that affects all cat breeds and has two distinc forms: effusive and non-effusive. In the effusive form, there is a common type of vasculitis that causes extravasation of fibrin-rich fluid, resulting in the accumulation of yellow exudative fluid in the body cavities. In the present study, we aimed to evaluate the organ distribution and severity of the pathological alterations associated with granuloma and vasculitis. It also seeks to describe FIPV antigen localization in FIP lesions. For this purpose, necropsies were performed on eight cats suspected of having died from FIP at the Faculty of Veterinary Medicine, Kırıkkale University. Tissue samples were routinely processed for immunohistochemical analysis. FIPV antigen was detected using immunoperoxidase staining, and the immunopositivity of vasculitic and granulomatous lesions in various organs was evaluated semi-quantitatively for each tissue sample. In effusive FIP cases, peritoneal fluid accumulation was significantly more common, and the lesions were characterized by granulomas progressing through the serosa of the intestine, kidney and liver. Vasculitis lesions, usually affecting small and medium-sized vessels, were characterized by endothelial hypertrophy and swelling, edema and hyalinization of the muscular layer, and adventitial neutrophil leukocyte and macrophage infiltration. Granulomas were characterized by microscopic findings with dense infiltration of macrophages and lymphocytes around a few thrombotic and/or degenerative vessels in the center. In the examined cases, FIPV antigen immunopositivity varied according to the organ involvement in each case, but was frequently concentrated around the periphery rather than in the center of vasculitis and granulomatous lesions.