Outbreak of Cutaneous Papillomatosis in Buffaloes (Bubalus bubalis): Diagnosis by Transmission Electron Microscopy

Papillomatosis is an emerging infectious disease that causes significant economic losses in intensive and semi-intensive buffalo production systems. In dairy herds, the disease impairs milking, causes cutaneous lesions and bleeding, and predisposes animals to mastitis. In beef production systems, the main impacts include reduced weight gain, hide damage, and increased veterinary care costs. The disease may occur in cutaneous and mucosal forms. The cutaneous form is characterized by the presence of warts or fibropapillomas distributed throughout different regions of the body, whereas the mucosal form is associated with bovine enzootic hematuria and urinary bladder carcinogenesis. The lesions observed include papillomas, fibropapillomas, and fibromas, as well as verrucous lesions affecting the mucosa of the rumen, oral cavity, esophagus, and amniotic membrane. Transmission occurs mainly from animal to animal and is facilitated by injuries to the skin and mucous membranes caused by fences, water troughs, feeding troughs, or instruments used for animal restraint. Bovine papillomaviruses are double-stranded DNA viruses belonging to the family Papillomaviridae. In 1993, fibropapilloma samples from five buffaloes (Bubalus bubalis) originating from a farm located in the municipality of Registro, São Paulo State, Brazil, were submitted to the Electron Microscopy Laboratory of the Biological Institute, São Paulo, Brazil. The samples were processed using transmission electron microscopy, negative staining, and resin embedding techniques. In all samples, a large number of non-enveloped papillomavirus particles with icosahedral symmetry were observed. These particles were characterized as "full" and "empty" virions, measuring approximately 60 nm in diameter. In ultrathin sections of papilloma fragments, intracytoplasmic viral particles measuring approximately 30 nm in diameter were observed, associated with thickening of the plasma membrane, which exhibited a serrated appearance. In addition, intranuclear viral particles and membrane-bound intracytoplasmic vacuoles were identified. In the reticular layer, a nucleus with an irregular contour, marginalized chromatin, and the presence of viral particles was observed. The results confirm the occurrence of papillomatosis in buffaloes and demonstrate the importance of electron microscopy for the rapid diagnosis and morphological characterization of the viral agent.