According to petMD, warts on dogs' mouths are generally caused by canine papillomavirus. Most often, these warts are benign tumors that fall off on their own, but in some cases they become malignant tumors and require surgical removal. The removal of a malignant tumor from a dog should be performed by a practitioner of veterinary medicine.
petMD states that symptoms of canine papillomavirus include bleeding from the mouth, excessively bad breath associated with oral papillomatosis, increased or decreased appetite and excessive saliva excretion. Papillomatosis is contagious among dogs but is sometime caused by breed-related genetic factors. If the lesions potentially caused by papillomavirus are oral, veterinarians generally take a biopsy to test for the virus and determine if it is the actual cause.
If tumors must be removed from the dog's mouth surgically, the dog is unable to eat properly during recovery. A veterinarian advises the pet owner on the correct foods to feed the dog during recovery. Follow-up visits are necessary to determine whether warts have become malignant and a danger to the dog, notes petMD. To prevent the spread of canine papillomavirus, dogs that are infected with the disease should not be in the company of uninfected dogs due to the virus' contagious nature.