Fibropapillomas, also called papillomas, are what most people call the common wart. They are composed of skin and connective tissue cells and are extremely contagious between dogs by either direct or indirect contact. Fortunately, they are not transmitted from dogs to people or to cats.
Causes of Canine Warts
Warts are external growths caused by any of a number of papilloma viruses – a group of DNA viruses that induce proliferative, species-specific and usually benign skin and oral tumors in dogs. The underlying cause is thought to be largely immune-mediated, and there appears to be a genetic component in certain breeds. Dogs on chronic corticosteroid therapy frequently become immunocompromised and are more likely to develop papillomas. Infection by a papilloma virus requires inoculation through a break in the skin or mucosa, normally through direct contact with lesions on an infected dog, or possibly through contact with contaminated veterinary instruments or other items carrying the virus.
The incubation period for canine papilloma viruses is usually 1 to 8 weeks from contact with an infected dog. The warts typically regress within 5 months, but they can persist for years.
Prevention of Canine Warts
There is no foolproof way to prevent warts in dogs. Dogs known to have oral papillomas should be kept away from susceptible dogs, because the condition is quite contagious. Chronic use of corticosteroids should only be used when medically necessary, because it reduces a dog's ability to fight infection. A papilloma virus vaccine is under development and shows promise.
A number of skin conditions can be confused with warts, some of which are very serious. All lumps and bumps on dogs should be checked by a veterinarian. If surgical removal of a wart is recommended, it can be accomplished by traditional surgical excision, cryosurgery, laser ablation or electrosurgery/electrocautery. Warts are not transmittable between dogs and people, because they are species-specific. However, they are highly infectious between dogs.
Canine warts (fibropapillomas or papillomas) are typically seen by owners as raised bumps or lumps around their dog's mouth or on the lower limb extremities. They may or may not bleed or be irritated by scratching or chewing.
Symptoms of the Disorder
Canine papillomas can appear anywhere on a dog's body and usually look like tiny cauliflowers, but occasionally they are smooth. Older dogs tend to develop isolated warts, commonly on the feet, around the toes and footpads and on the under-belly. These warts can start and stay small, or they can increase in size. Young dogs usually develop warts in clusters, often inside the mouth, around the eyes or elsewhere on the face or genitalia. Puppies are especially prone to developing warts, because they have naïve immune systems and commonly lick and romp rambunctiously with other dogs.
Warts are painless and generally do not require treatment for medical reasons. They can be removed for cosmetic reasons, or if they cause the dog discernable discomfort (such as lameness when they are between the toes or affecting the footpads, or when they interfere with vision or eating). While warts are usually harmless, they can bleed and become ulcerated, infected and painful if scratched or chewed. Uncommonly, they transform to malignant squamous cell carcinoma. Canine warts often regress spontaneously within one year.
Dogs at Increased Risk
Young dogs and dogs with compromised immune systems – especially those with damaged skin or mucous membranes - are predisposed to developing papillomas. Cutaneous papillomas are more common in intact males, probably because of their tendency to be aggressive and to engage in physical confrontations with other dogs. Cocker Spaniels, Pugs, Miniature Schnauzers and Kerry Blue Terriers tend to develop warts more frequently than do other breeds.
Warts in dogs are not difficult to diagnose. They are typically visually observable, and owners tend to notice them and point them out to their veterinarians during routine annual check-ups.
How Canine Warts are Diagnosed
Papillomas in dogs are fairly identifiable just by their appearance. They can occur singly or in clusters, and often have a cauliflower-like appearance. They are common on the lips and gums, but also commonly occur on the dog's lower legs (distal extremities). They look like what we refer to as "warts." Basically, they are raised, lump-bumpy masses either singly or in clusters.
Advanced diagnostic techniques include biopsy of the mass and immunohistochemistry to identify the particular papilloma virus that caused the condition. Other protocols are polymerase chain reaction testing to identify the cause of cutaneous papillomas, and electron microscopy. Electron microscopy is usually used primarily for research rather than for clinical diagnostic purposes in pet dogs.
Sometimes, benign neglect is the treatment of choice for canine papillomas. However, owners should be aware of the highly contagious nature of this infectious condition. Canine "warts" are not simply a nuisance. They are caused by a virus that can easily be transmitted to other dogs by physical contact.
Canine "warts" are benign growths caused by any number of species-specific and site-specific papilloma viruses. Dogs that develop solitary or even clusters of warts may not need treatment. However, in some cases, the growths become ulcerated, infected and painful, especially if they are scratched or chewed, which can cause mild to severe discomfort – particularly when they involve the mouth, toes and/or foot pads. If this happens, the papillomas probably should be removed. Sometimes, owners will elect to have the papillomas removed purely for cosmetic reasons.
Many oral mucosal and other papillomas are self-limiting and regress spontaneously without surgery once the dog mounts an appropriate immune response. If surgical removal is necessary or otherwise desired, it is normally accomplished by traditional excision, cryosurgery, laser ablation or electrosurgery/electrocautery.
Electrocautery essentially involves using electricity to burn off the affected tissue. This procedure can be performed using a local anesthetic, so that the dog does not have to be intubated and put under general anesthesia. Cryosurgery involves freezing the growth, which also normally can be accomplished using a local anesthetic. Laser ablation is most often used for persistent cases involving large numbers of lesions, or those that are refractory to other treatment options. It typically requires general anesthesia.
Injectable subcutaneous interferon treatment, multiple times a week for up to 8 weeks, has been anecdotally reported to be helpful in cases of viral canine papillomas. Interferon can cause a number of unpleasant side effects, including fever, joint pain, nausea, inappetance and dizziness. A relatively new recombinant canine oral papillomavirus vaccine, developed by Georgetown University Medical Center, has shown promise. Other treatments are in development as well.
The prognosis for dogs with "warts" is generally quite good, especially since most papillomas regress on their own. It is possible, but highly unlikely, that papillomas can transform to malignant squamous cell carcinoma. Any lumps or bumps on our beloved companion dogs should be monitored and assessed by a veterinarian regularly.