Introduction
What we call “warts” are actually lesions caused by papilloma viruses – a group of DNA viruses that induce proliferative, site-specific and usually benign skin and mucosal tumors in dogs. These lesions are contagious between dogs, but not to people or to cats. Pet owners do not have to be concerned about becoming infected with warts from their dogs.
Types of Warts
Papillomas in older dogs can appear anywhere on the body, though they tend to develop more often on distal extremities, such as around the toes and footpads, and on the abdomen. In most of these cases, older dogs affected by papillomas are immunocompromised, often due to chronic use of glucocorticoids. These warts can start and stay small, or they can grow larger over time. Papillomas generally do not need to be treated for medical reasons, although they can be removed for cosmetic reasons or if they cause the dog discomfort (often lameness when they are between the toes or affecting the foot pads). While canine papillomas are usually harmless, they can bleed and become infected if scratched or chewed. Uncommonly, they malignantly transform to squamous cell carcinoma, which is a much more serious problem. If you notice what looks like a “wart” on your older dog, it is a good idea to watch it closely. If the lump grows, changes color or shape or becomes infected, have your veterinarian examine your dog and advise you on the best next step to address this condition.
Warts also occur in younger dogs from 6 months to 4 years of age – especially inside the oral cavity and in clusters around the eyelids, mouth, lips, tongue or muzzle. These masses often have a “cauliflower”-like appearance and begin as small, smooth pale nodules that progress to darker pedunculated masses with frond-like projections. As with cutaneous papillomas, tumors involving the oral or ocular membranes can be spread by direct contact between dogs, which often happens when they lick and greet one another. Young dogs are more likely to develop papilloma lesions because they are still immunologically naive and tend to romp and play more roughly than older dogs, causing damaged skin and mucous membranes. Canine papillomas often regress spontaneously. They certainly can be removed surgically if they bother the owner or the affected animal.