Histopathology of Papillomavirus Lesion in Carp (Cyprinus carpio)

Abstract

Papillomavirus (PV) is a small circular double-stranded DNA virus of the Papillomaviridae family, widely distributed among vertebrates and characterized by high tropism for keratinized and mucosal epithelia. This study performed a histopathological evaluation of a cutaneous lesion found in a carp (Cyprinus carpio) from a fish farm in Rio Grande do Sul, Brazil, suspected of Papillomavirus infection. The specimen was euthanized and necropsied, and samples of skin and internal organs were collected for histological examination. Samples were fixed in 20% buffered formalin, processed in paraffin, and stained with hematoxylin and eosin. Microscopic evaluation revealed hyperkeratosis, acanthosis, papillomatosis, and eosinophilic intranuclear inclusions suggestive of viral replication. Koilocytes with perinuclear halos and nuclear displacement were identified, serving as pathognomonic markers of Papillomavirus infection. The stroma exhibited basement membrane disruption and diffuse lymphoplasmacytic infiltration. These histological findings are consistent with a diagnosis of cutaneous papillomatosis, confirming viral etiology. This study highlights the relevance of histopathology as a primary diagnostic tool for differentiating epithelial proliferative lesions in fish, emphasizing the need for subsequent molecular confirmation.