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

The research discusses the first identified case of prolonged infection with equine papillomavirus type 2 (EcPV-2), leading to extensive papilloma growth on a horse’s penis, an unusual scenario that suggests the virus can cause persistent infection in horses. This understanding could aid in preventing equine penile squamous cell carcinoma, a cancer linked to EcPV-2.

Case Presentation and Diagnosis

• A 9-year-old gelding was presented with roughly 100 papillomas on its penis, covering approximately 75% of the area.
• A biopsy was performed, and histological examination revealed signs of a viral disease, including koilocytosis and cytopathic alterations, which are characteristic of infection with viruses that cause warts.
• Using Polymerase Chain Reaction (PCR) on DNA taken from the sampled tissue, the researchers have identified the presence of EcPV-2, a type of virus responsible for causing papillomas in horses.

Follow-up and Persistence of the Infection

• After sixteen months, the horse was re-examined and the papillomas remained unchanged in appearance.
• PCR was used again on samples from biopsied tissue and penis swabs, with EcPV-2 DNA sequences detected in both sets of samples.
• The virus was specifically linked to the lesions through immunohistochemistry and in situ hybridization, two techniques used to locate certain proteins or DNA sequences within a tissue sample.
• Two years after the horse’s first presentation, no change in the appearance of the papillomas was observed.

Interpretation and Implications

• The extensive number of warts and their persistence, despite a prolonged period, support diagnosing the condition as papillomatosis, a disease characterized by development of numerous papillomas.
• This case study is significant as it is the first documented evidence demonstrating that EcPV-2 can cause continuous infection in horses.
• The understanding of the natural progression of EcPV-2 infection could be crucial in preventing equine penile squamous cell carcinoma, a type of cancer that is believed to be promoted by the EcPV-2 virus.