Causes of Canine Warts
Warts, also called papillomas or fibropapillomas, are species-specific, usually benign external growths that are caused by a number of different double-stranded DNA viruses in the family Papillomaviridae. In domestic dogs, warts commonly show up on the skin (cutaneous papillomas) and in the mouth (oral cavity papillomas). They also develop on the eyelids, face, feet and footpads and on the external genitalia. Why some dogs develop warts while others do not is probably affected by the strength, weakness or maturity of the dog’s immune system.
Certain breeds seem to have a genetic predisposition to developing warts. Dogs that are on long-term corticosteroid therapy often have weakened immune systems, which cause them to become immunocompromised and more susceptible to contracting contagious diseases. Young puppies also are immunocompromised and are more likely to develop warts than are mature animals because of their naïve immune systems. The papilloma viruses that cause canine warts are highly contagious between dogs. Infection typically requires inoculation through a break in the skin or mucosa, which normally happens when one dog comes into direct contact with wart lesions on an infected dog.
These viruses are relatively stable in the environment and can also be transmitted indirectly, such as through contact with contaminated grooming tools, veterinary instruments or other non-living items that carry the viral organisms; these are called “fomites.” Fortunately, the wart viruses that affect dogs are not contagious to cats or to people. The incubation period for canine papilloma viruses is usually 1 to 8 weeks from contact with an infected dog. The warts may spontaneously regress several months, but sometimes they will persist for years.
Prevention of Canine Warts
There is no foolproof way to prevent dogs from developing warts. Dogs with warts on their skin or in their mouth should be kept away from susceptible dogs, because the viruses that cause warts are quite contagious. Chronic use of corticosteroids should only be done when absolutely necessary, because long-term steroid use weakens the immune system and reduces the body’s ability to fight infection. A canine papilloma virus vaccine is under development and shows promise.
A number of skin conditions can be confused with warts; some of these are very serious. All suspicious lumps and bumps on dogs should be checked by a veterinarian. If the doctor recommends removing the wart, it usually can be done by a simply surgical excision. Cryosurgery, laser ablation and electrosurgery/electrocautery are other methods that can be used to remove warts. Warts are not transmittable between dogs and people, because the viruses that cause them are species-specific. However, they are highly infectious between dogs.