Canine papillomavirus (CPV) is a group of viruses that cause warts and other skin growths in dogs. There are currently 24 identified types of CPV, and most cause benign growths that resolve on their own within weeks to months. The virus is most common in young dogs between 6 months and 2 years old, whose immune systems are encountering it for the first time. While the warts are usually harmless, certain types of the virus can, in rare cases and under specific conditions, lead to more serious problems.
What Canine Papillomavirus Looks Like
The most recognizable form is oral papillomatosis: clusters of small, raised growths inside the mouth, on the lips, tongue, or gums. These warts typically have a rough, cauliflower-like surface, appear white to gray in color, and range up to about 1 to 2 centimeters across. Oral warts tend to be larger than those that appear on the nose or lips. The growths are firm, project outward from the skin or mucous membrane, and often sit on a narrow stalk.
Warts can also appear on the skin (cutaneous papillomas), and these are considered the second most common skin tumor in dogs under one year of age. A distinct form called pigmented plaques looks different: flat, dark-colored patches on the skin rather than raised bumps. Pigmented plaques tend to show up in middle-aged dogs rather than puppies and are associated with certain breed predispositions, particularly in Pugs and Vizslas.
How Dogs Get Infected
Dogs pick up the virus through direct contact with an infected dog’s warts or by encountering the virus in shared environments like dog parks, daycare facilities, and boarding kennels. The virus needs tiny breaks or scratches in the skin or mucous membranes to establish an infection, so rough play, shared toys, and communal water bowls can all create opportunities for transmission.
After exposure, there’s an incubation period of roughly 4 weeks before any visible warts appear. During a documented outbreak at a dog daycare facility, nearly all infections could be traced to contact with an incubating or symptomatic dog within that 4-week window, though slightly longer incubation periods may be possible. It’s still unknown whether dogs can spread the virus before visible warts develop, which makes outbreaks in group settings difficult to prevent. Subclinical infections, where a dog carries the virus without ever showing visible warts, are also believed to occur.
Which Dogs Are Most at Risk
Young dogs are the most commonly affected because they lack prior immune exposure to the virus. Most healthy puppies and adolescent dogs mount a strong immune response that clears the infection naturally.
The dogs that run into trouble are those who cannot mount an adequate immune response. This includes dogs on immunosuppressive medications and, less commonly, dogs with an immune defect that seems specific to papillomavirus. Persistent warts, defined loosely as continued development of new growths six months or more after the initial infection, are rare but serious. Dogs with persistent warts sometimes develop such extensive growths that the condition significantly affects their quality of life. Certain breeds appear genetically predisposed to developing pigmented plaques, with Pugs and Vizslas overrepresented.
How Vets Diagnose It
Many veterinarians can identify classic oral warts on sight based on their distinctive cauliflower-like appearance and typical location. When the diagnosis is less clear, or when a growth looks unusual, a biopsy provides more detail. Under the microscope, papillomavirus-infected tissue shows characteristic changes in skin cells, including cells with distinctive halos around their nuclei that are a hallmark of papillomavirus infection.
However, microscopic examination alone cannot distinguish between the different types of CPV or rule out other skin conditions that look similar. For a definitive answer, molecular testing such as PCR is used to detect the virus’s genetic material directly. PCR and similar molecular techniques are considered the gold standard for diagnosis because of their high sensitivity and specificity. This level of testing matters most when warts are persistent, atypical, or there’s concern about possible malignant changes.
How Long Warts Last and When They Go Away
The timeline depends heavily on which virus type is involved and the dog’s immune system. Oral warts caused by CPV-1, the most common type, typically regress on their own within 4 to 8 weeks. The immune system recognizes the virus, mounts a response, and the warts shrink and disappear without treatment.
Skin warts caused by CPV-2 are a different story. These tend to be more persistent, often lasting longer than 6 months. In one documented case, a dog’s footpad warts caused by CPV-2 spontaneously regressed two weeks after a biopsy was taken, suggesting that the minor tissue disruption from the biopsy may have helped trigger an immune response. This kind of spontaneous resolution after biopsy has been observed in dogs that are otherwise healthy and not immunocompromised.
Treatment for Persistent Cases
Because most warts resolve on their own, treatment is typically reserved for cases where the growths are severe, persistent, or causing the dog problems like difficulty eating, excessive drooling, or pain. Several options exist for those cases:
- Surgical removal: Warts can be cut away using electrocautery or standard surgical excision. This is the most direct approach for large or problematic growths.
- Cryotherapy: Freezing the warts off, similar to how human warts are sometimes treated.
- Laser therapy: CO2 laser ablation can remove warts, sometimes repeated every 2 to 4 weeks for extensive cases.
- Topical immune-stimulating cream: Applied directly to warts to boost the local immune response against the virus.
- Oral antibiotics with immune-modulating properties: Sometimes prescribed alongside other treatments, though effectiveness varies.
In one severe case of progressive oral papillomatosis that did not respond to oral antibiotics or injectable immune-stimulating therapy, a combination of laser ablation and a custom vaccine made from papillomavirus proteins was used over a 20-week course. This kind of intensive treatment is unusual and reserved for the most stubborn cases.
The Risk of Cancer
In the vast majority of dogs, papillomavirus causes nothing more than temporary, benign warts. However, there is a small but real risk that certain virus types can contribute to squamous cell carcinoma, a type of skin cancer. This progression from benign wart to cancer has been documented, with papillomas showing a stepwise progression from precancerous changes to invasive cancer.
Several factors increase this risk. Immunosuppression is the most significant: dogs on long-term immune-suppressing medications or with compromised immune systems are more vulnerable. Ultraviolet radiation exposure may also play a role, potentially enhancing the cancer-promoting effects of the virus. Certain CPV types are more frequently associated with cancerous changes than others. The virus types linked to pigmented plaques (CPV-3, 4, 5, 8, and several others) carry a higher association with skin squamous cell carcinoma, while some types found in oral warts have been linked to oral cancers.
This risk is the main reason veterinarians take persistent or unusual-looking warts seriously, especially in older or immunocompromised dogs. Any growth that changes in size, color, or texture, or that doesn’t resolve within a reasonable timeframe, warrants closer evaluation.
Can Dogs Pass It to Humans?
Papillomaviruses are highly species-specific. The 24 types of canine papillomavirus infect dogs, not people. Humans have their own set of papillomaviruses (HPV), and while the biology is similar, the viruses do not cross between species. You cannot catch warts from your dog, and your dog cannot catch them from you.
The virus can, however, spread readily between dogs, which is why outbreaks at daycares, shelters, and dog parks are common. If your dog develops warts, limiting contact with other dogs during the active infection is a reasonable precaution, particularly around puppies or dogs with known immune issues.