Equine congenital papilloma: pathological findings and results of papillomavirus immunohistochemistry in five cases.

This study investigates the potential causes of congenital cutaneous papillomas, abnormal growths on the skin, in young horses, suggesting that these may not be caused by viral infection as initially believed, but could be naturally occurring lesions.

Summary of Study and Findings

The paper discusses a pathological study conducted on five foals, aged from 305 days in utero to 2 days old, diagnosed with congenital cutaneous papillomas. The breeds of these horses varied, with two Thoroughbreds, one standard-bred horse, one warmblood horse, and one Paint horse. The study provided insight into:

• The physical properties of the growths. It was observed that the masses were pendulous and varied in surface texture, appearing either smooth and cauliflower-like or rough and wart-like.
• The locations of these masses. The study found that these growths could occur as single lesions on parts of the body such as the forelimb, lip and face, or as multiple lesions on the trunk of the horse.
• The specific characteristics of the cell changes. Despite the masses’ similarities to viral papillomas, analysis of the tissue features revealed no evidence of nuclear or cytoplasmic changes, which are characteristic of viral infections. One case showing epidermal proliferation also had proliferation of pilosebaceous units, suggesting that these might not be viral growths.
• The negative results from immunohistochemical studies carried out to detect the presence of papillomavirus antigens. The study found that all tested cases did not show evidence of these antigens, further suggesting that viral infection is not the cause of these papillomas.

Implications and Conclusions

These findings suggest that equine congenital papilloma might not be a viral-induced growth after all, contrary to previous conceptions. Instead, the results indicate that these skin growths might be a type of skin lesion known as an epidermal nevus. This newer interpretation of the cause of equine congenital papillomas could lead to a revision in our understanding of both the occurrence and treatment of these growths in the horse population.