Dog warts

What causes warts in dogs?

Warts, also known as papillomas, are benign (non-cancerous) skin tumours caused by a virus.

Lots of different species can catch their own, specific papilloma viruses, including humans – verrucas are warts caused by human papilloma virus (HPV). There are a number of dog papilloma viruses, or CPVs. Once a dog has recovered from a CPV, they become immune to it, but could still be susceptible to other types of CPV.

It’s normal for animals to carry viruses asymptomatically but, in young or immunocompromised dogs, for instance, those who are on medication to control allergy symptoms, warts can develop until the body generates a strong enough immune response to get rid of them.

Papilloma viruses can survive for a long time in the environment, and they gain access when skin becomes damaged, for example, by abrasions or insect bites. They can be spread by direct contact with another dog who has a wart, or when viral particles contaminate equipment like bedding or food bowls.

Symptoms of warts in dogs

Although warts can have a characteristic appearance, not all do.

They’re usually knobbly or raised and feel soft-to-firm. Dog papillomas in and around the mouth are often described as having a ‘cauliflower-like’, or ‘sea anemone’ appearance.

If you discover skin warts with your fingers, you might at first wonder whether you’ve found a tick. However, whereas ticks are normally smooth and purplish in colour, and have a narrow base where the mouthparts are buried in the skin, warts are more often pink, white or grey and have a wider base or are occasionally almost flat. Some kinds of dog warts can grow to over 2 cm in diameter.

There are certain sites where you’re more likely to find specific types of warts. Different papilloma viruses are associated with particular parts of the body and with either younger or older dogs.

In dogs under two years old, canine oral papillomas, caused by CPV-1 are commonly seen in and around the mouth and muzzle, or sometimes around the eyes or between the toes. They appear suddenly in clusters and spread quickly.

Dogs of any age can get single papillomas on the skin, the genitals and under or on the eyelids.

One type of viral wart, called cutaneous inverted papilloma (CIP), grows inwardly and is usually found on the tummy or on the feet, including the pads, which can be painful like a verruca. CIPs sometimes occur inside the ears and under the neck of predominantly young adult dogs. Occasionally, warts are also seen on the genitals.

If you discover lesions on your dog’s skin, always contact your vet, even if you’ve previously had similar-looking lumps or bumps checked. Although warts are usually harmless unless they get knocked or infected, occasionally, they can progress to a form of skin cancer called squamous cell carcinoma, which requires treatment. It isn’t possible to tell whether a dog wart has become cancerous without performing further investigations.

How are warts investigated in dogs?

If you take your dog to the vet with suspected warts, they may be confident to confirm the diagnosis based on the appearance and site of the lesions, especially if your dog is young and the warts are on their mouth area. 

For any other warts, your vet may ask you to monitor them, or they may recommend investigation. The simplest way to check a wart is to use a needle and syringe to suck up cells from within it and look at them under a microscope, either at the clinic or by sending them to a specialist laboratory.

A surgical biopsy, where the removal of a dog’s wart, or part of it, is another way to find out what a lump or lesion is. This provides the most accurate information because the structure of the tissue is preserved in the sample, but it usually requires sedation or general anaesthesia to perform it. 

If your vet asks you to monitor any lump or bump on your dog, take photos and measurements every two weeks, and check how the lump feels. When you take photos, make sure the lighting is good and put something else in the picture, such as a coin or the end of a tape measure, to provide an accurate scale. If you think a wart or lump is changing, or if it’s bothering your dog or getting knocked, go back to your vet so that plans can be made to investigate it.

What is the treatment for dog warts?

The good news is that, in young dogs, warts normally clear up by themselves once the immune system matures. This normally takes one to two months. If a wart is still there after three months, it should be checked by a vet and may need to be biopsied to make sure it really is just a viral papilloma. Sometimes, dogs taking immunosuppressant medication, for instance, those with allergies, may need to be given treatment for viral warts to help get rid of them.

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For dogs with large numbers of warts in or around their mouth, eating and drinking can become uncomfortable. Papillomas can be frozen off or they can often be removed surgically. If papillomas become infected with bacteria from within the mouth, they can cause discomfort and bad breath and may require antibiotics. 

If a dog has a wart on their eyelid, it may scratch the cornea when the dog blinks, so it won’t be possible to wait for it to resolve on its own. Also, more serious lumps that look like eyelid warts in dogs sometimes occur, so any lump on a dog’s eyelid should always be checked by a vet as soon as you notice it. 

Various treatments have been tried for stubborn warts on dogs, including anti-viral medications and ‘wart vaccines’, but it’s difficult to know how successful these are, partly because warts usually disappear once the immune system overcomes them.