Persistent, widespread papilloma formation on the penis of a horse: a novel presentation of equine papillomavirus type 2 infection

Abstract

A 9-year-old gelding presented with approximately 100 papillomas that covered about 75% of the distal penis. Biopsy was performed, and histology showed evidence of viral cytopathic change and koilocytosis. Polymerase chain reaction using DNA extracted from biopsied tissue amplified equine papillomavirus type 2 (EcPV-2) DNA sequences. Sixteen months later, the horse was re-examined and the appearance of the papillomas was unchanged. Equine papillomavirus type 2 DNA sequences were again amplified from both biopsied tissue and swabs of the penis. Papillomavirus was localized to the lesions by immunohistochemistry and in situ hybridization. An examination 2 years after the initial presentation revealed no detectable change in the appearance of the penis. The large number of papillomas and their failure to regress over an extended period support a clinical classification of papillomatosis. To the authors' knowledge, this is the first report of papillomatosis of the equine penis. This novel clinical manifestation suggests that persistent EcPV-2 infection is possible in horses. As there is evidence that EcPV-2 may promote development of equine penile squamous cell carcinoma, understanding the natural history of EcPV-2 infections may be important in preventing equine penile neoplasia.

Expression of p53, Ki67, EcPV2‐ and EcPV3 DNA, and viral genes in relation to metastasis and outcome in equine penile and preputial squamous cell carcinoma

“…There are various indications that infection with EcPV2 plays an important role in the pathogenesis of penile cancer in the horse . The current study supports this, as 90.1% of the samples were positive against only one positive result in 12 samples from normal penile skin.…”

Generalized papillomatosis in three horses associated with a novel equine papillomavirus (EcPV8)

“…These areas were sometimes involved in our cases but less prominently. The two younger horses exhibited thousands of coalescing papillomas, which is more than other equine papilloma clinical entities …”

Serum antibodies and DNA indicate a high prevalence of equine papillomavirus 2 (EcPV2) among horses in Switzerland

“…Several studies have indicated a connection between EcPV2 and clinical conditions such as genital papillomas and in situ and invasive squamous cell carcinomas . There is evidence that the viral DNA can be found in most clinical samples but only occasionally in other lesions or clinically healthy skin . While papillomavirus infections in humans have been shown to be mandatory for the development of certain lesions, an overt clinical manifestation, especially malignant transformation, is also dependent on other factors .…”