Large Superficial Papillomas on the Fetlock of a Horse

The importance of a biopsy when dealing with unknown skin conditions is the take home message of this piece. Also of interest is the treatment with imiquimod not a product I am familiar with. No not specifically an antiviral it does have some immune response activity. It may attenuate the bodies inflammatory reaction to the papillovirus while stimulating the immune system to attack the virus. I found this on WebMD:

“Imiquimod is used to treat actinic keratoses (AK) which are precancerous growths on the skin. AK are caused by too much sun exposure. Treating this condition can decrease the risk of complications from them. It is also used to treat warts on the outside of the genitals/anus. Imiquimod belongs to a group of drugs called immune response modifiers. It is believed to work by helping to activate your immune system to fight these abnormal skin growths.”

Detection of a Putative Novel Papillomavirus Type within a Large Exophytic Papilloma on the Fetlock of a Horse
Pathogens. 2020 Oct 5;9(10):E816.
Authors
John S Munday 1 , Michael R Hardcastle 2 , Melissa Sim 3
Affiliations

1 School of Veterinary Science, Massey University, Palmerston North 4410, New Zealand.
2 Gribbles Veterinary Pathology Ltd., Auckland 1060, New Zealand.
3 Franklin Vets, Pukekohe 2120, New Zealand.

Abstract

A 10-year-old horse presented with two 3-cm diameter exophytic masses over the fetlock. Histology was consistent with a hyperplastic squamous papilloma and numerous cell changes consistent with papillomavirus (PV) infection were visible. Partial sequences of PV L1 and E1 ORFs were amplified using consensus PCR primers. The sequences were most similar to Equus caballus type 1 (EcPV1). However, as the sequences were only around 73% similar to EcPV1, they appear to be from a novel PV type that is likely to be within the Zetapapillomavirus genus. The papillomas were treated with topical imiquimod and resolved within 14 weeks. The clinical presentation of the papillomas in the present case had marked differences to the clinical presentation of EcPV-1-induced papillomas, which are typically small, numerous and around the face. Observations from the present case increase the clinical spectrum of PV-induced lesions in this species as well as providing evidence of an additional novel papillomavirus that is able to cause disease in horses.