The increase in social interaction in dogs associated with the growing popularity of dog parks and dog day care facilities has resulted in an increase in canine patients presenting with papilloma virus associated dermatoses. Papillomaviruses are non- enveloped DNA viruses, which are transmitted by direct and indirect contact and specifically infect epithelial cells. Infection occurs at the site of damaged skin or mucous membranes with viral incubation lasting 1 to 2 months. Papillomavirus is fairly stable in the environment and can survive for 63 days at 4° to 8° C or for 6 hours at 37°C.
Canine oral papilloma is most often a self-limited infectious disease that is normally confined to the mucosal tissue of the oral cavity or lips in young dogs. The disease occasionally produces papillomas on the conjunctiva and external nares. Lesions start as smooth white papules or plaques and progress over 4 to 8 weeks to pedunculated or cauliflower-like hyperkeratotic masses. In most patients the lesions will regress in another 4 to 8 weeks. Regression is the result of the development of a cell mediated immune response and animals typically develop solid immunity as a result of previous exposure to the virus. In some rare cases dogs appear to have a specific immune deficiency and lesions do not regress and are non responsive to any form of treatment. Administration of immune suppressive/modulating drugs and chemotherapy can lead to the development of papillomavirus associated lesions.
Cutaneous inverted papillomas present as a single mass or as multiple small masses. They are unpigmented, raised, firm and covered by skin with a central pore opening to the surface. Lesions are usually seen in dogs younger than 3 years, although older dogs may be affected. Masses are commonly found on the ventral abdomen and groin but may appear on the distal limbs, footpads and interdigital areas. These lesions do not typically regress and surgical removal is required in most patients for cure.
Canine pigmented plaques are found mainly in pugs, miniature schnauzers and French bulldogs during young adulthood. There may be an inherited autosomal dominant trait and immunocompromised individuals are suspected to have an increased incidence of this disease. Lesions are typically multiple and present as papules and plaques and are typically deeply pigmented and sometimes papillated. Lesions develop progressively over time and generally do not regress.
In most patients, canine oral papillomas will resolve over time. In cases that fail to regress, macerating or traumatizing their lesions may help induce regression. Azithromycin at an oral dose of 10 mg/kg once daily for 10 days has been shown to sometimes be effective in the treatment of oral papillomas. The exact mechanism of action is unknown. Human data indicates azithromycin increases the production of interferon-stimulated genes in certain cell lines. Interferon exerts a biological action that protects cells from viral infection. Administration of IFN-α-2a at 1.5 to 2 million units SQ three times weekly has been reported to be effective in severe cases of oral and cutaneous viral papillomatosis. Administration of feline recombinant interferon – ω at 1 million units SQ once daily for 5 days and repeated 14 days later has been effective in treating severe oral papillomas