All About Warts in Cats

Magically popping up, seemingly out of the blue, warts are rough growths that protrude from the skin. Occurring in one of every three children and teenagers, warts also occur in adults with weakened immune systems.

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Resembling a small cauliflower or solid blister, papillomas, commonly known as warts, have given toads and frogs a bad name over the years, as many people erroneously believe handling the amphibians causes warts. However, warts are, in fact, an infection of the epidermis, or top layer of the skin caused by the human papillomavirus, also known as HPV or "human pap."

But warts don't only affect people. Over 100 unique types of viruses cause warts in all animal species, including our pet cats, and more often, dogs. As you might expect, each species of animal has its own viruses and related tumors. And although warts in cats often erupt in clusters, and they are indeed, tumors, the weird little bumps are often benign. But keep in mind, if you have a cat older than 10, papillomas can lead to the formation of feline multicentric squamous cell carcinoma in situ, otherwise known as feline Bowen disease.

If your cat has been infected with a papilloma virus, you''ll want to know everything you never wanted to know about warts.

What causes warts on cats, and how do they develop?

Many cats carry the papilloma virus, and other viruses as well, asymptomatically, or without showing any clinical signs. Consequently, if your cat is healthy, you may never even know he has the virus because warts won't develop. However, if your cat is young, his immune system is immature and he won't be able to fight off infections, thus be more prone to developing papilloma warts. By the same token, if your cat is old, he may also be immunocompromised and could, as mentioned, develop feline Bowen disease if infected with the papilloma virus.

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Are you wondering where these papilloma viruses come from, anyway? They are transmitted through direct contact from an infected pet, or lurk in your cat's environment in bedding, toys, food, and water bowls.

The insidious attack begins when the virus gains access to the body through any area of the skin that is softened by moisture, like cuts, abrasions, and insect bites from ticks, fleas, and mosquitoes. Once in, the papilloma viruses invade a cat's cells, inserting their genetic information into the cat's DNA. This vile process upsets normal cell division, causing the cell to divide abnormally, and more frequently. In turn, this hostile virus takeover activates growth-promoting genes in the DNA called oncogenes. Simultaneously, suppressor genes that normally limit cell proliferation are inactivated, thus altering the genes that regulate normal, programmed cell death. Warts are not so simple after all!

And strangely enough, as randomly as they occur, warts will often spontaneously disappear as your cat slowly develops an immunity to them.

What problems can warts cause for my cat?

Warts in cats can become inflamed, infected, or sometimes they just won't go away. In these cases, surgical removal is often recommended by your veterinarian.

As in people, warts come and go on their own timeline, and moreover, often do not cause any problems. It actually all depends on the health of the individual cat. In healthy cats, warts will not spread to other areas of the body and regress on their own. In contrast, an immunosuppressed cat does not have the ability to fend off the virus's attack and more warts will appear.

Can I get warts from my cat?

Like human warts, cat warts are contagious, but only to other cats. Warts are species-specific growths so you and your family need not worry about contracting warts from your cat.

How are warts diagnosed?

Cats are prone to a multitude of lumps, bumps, and growths, some as mysterious as the felines themselves. Identifying which growths are potentially cancerous, or on the other hand, benign or nothing to worry about, is no easy task. That's why a trip to your veterinarian is important. She will want to evaluate any bumps or masses that are growing larger, changing in appearance, or are obviously irritating your cat. Because most warts have a typical appearance, your vet can most likely visually distinguish warts from other bumps. But a definitive diagnosis only comes after a fine needle aspiration, or FNA.

For this procedure, she will use a small needle with a syringe, and suction a sample of cells directly from the tumor. The tissue sample is examined by a veterinary pathologist under a microscope. If the results need further clarification, a biopsy may be necessary. Due to the usually small size of a wart, the entire tumor may be surgically removed for examination rather than just a piece of it. This diagnostic tool is known as histopathology.

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How are cat warts treated?

Thankfully, warts often disappear on their own without surgery because your cat develops immunity to the virus. Unfortunately, though, in unhealthy or old cats, papilloma viruses are often associated with squamous cell carcinoma cancer, or feline Bowen disease. Treatment in the form of surgery is usually recommended. Ditto for any warts that don't regress on their own within a couple of months.

Warts in cats with reduced immunity

Feline multicentric squamous cell carcinoma in situ, or feline Bowen disease, strikes cats with suppressed immune systems when they're over 10 years old or are ill. The warts in this case appear as multiple discrete red, black, or brown patches and bumps and develop due to the presence of a papillomavirus.

These lesions, like other warts, grow on the surface of the skin, but eventually morph into a tumor that spreads into underlying tissues yet likely won't spread to other parts of the body. Sadly, no treatment to date has proven to be completely successful. There is some hope, however, that treatments such as cryotherapy or freezing, localized radiation, and topical medications may control the lesions initially.