THE PET HEALTH LIBRARY By Wendy C. Brooks, DVM, DipABVP Educational Director, VeterinaryPartner.com

Does my Dog Have Warts?

photo courtesy of Dr. Jon Plant

A human finger with several viral warts

Certain viruses are able to cause the growth of small round skin tumors commonly referred to as warts. Everyone who has ever seen a drawing of a fairy tale witch knows what warts look like so when the family dog develops small round skin growths, many people assume these too are harmless warts. It is important to realize that viral warts are a specific condition and that a growth on the dog’s skin may or may not represent a viral wart.
Human warts are round, somewhat flat, and relatively smooth. Viral warts in dogs tend to possess frond-like structures creating more of a sea anemone or cauliflower-like appearance, though they can be smooth as well. The classical canine viral wart patient is a young dog with warts in or around the mouth or eyes. In cases where warts have a classic appearance in a classic patient diagnosis may be obvious, but in older patients with warts in locations other than the face, other types of growths become more likely. Because growths can appear harmless but behave malignantly, removal and biopsy are often recommended.

It is usually not possible to identify a growth visually though there are some exceptions.
Do not be surprised if what you are assuming is a wart is really something else.

In dogs, we do not call these growths warts; we use the more formal term viral papilloma. As in people, viral papillomas are caused by a papillomavirus though dogs and people have different papillomaviruses and cannot transmit their viruses across species lines.

What do these Papillomas look like?

sea anemone

Viral papillomas are round but often have a rough, almost jagged surface reminiscent of a sea anemone or a cauliflower. They occur usually on the lips and muzzle of a young dog (usually less than 2 years of age). Less commonly, papillomas can occur on the eyelids and even the surface of the eye or between the toes. Usually they occur in groups rather than as solitary growths.

Photo courtesy of Dr. Jan Bellows at www.dentalvet.com

How is this Virus Transmitted?

The infection is transmitted via direct contact with the papillomas on an infected dog or with the virus in the pet’s environment. The incubation period is 1 to 2 months. This virus can only be spread among dogs. It is not contagious to other pets or to humans. To become infected, the dog generally needs an immature immune system, thus this infection is primarily one of young dogs and puppies. Beyond this, transmission details are sketchy. It is not known whether the infected dog must actually show visible lesions to be contagious, nor how long after lesions have regressed that contagion is still a concern.

The canine papillomavirus has been shown to survive at least 2 months at temperatures of 40º F but only 6 hours at 98º F.
 
Are Viral Papillomas Dangerous?

Not really. They should go away on their own as the dog’s immune system matures and generates a response against the papillomavirus. There have been two cases published where viral papillomas progressed to malignancy but this is extremely rare and by no means the usual course of the infection. Typically, it takes 1 to 5 months for papillomas to regress, and growths in the mouth tend to regress sooner than those around the eyes.

Occasionally some papillomas will stay permanently.
Sometimes oral papillomas can become infected with bacteria from the mouth. Antibiotics will be needed in such cases to control the pain, swelling, and bad breath.

Treatment

In most cases, treatment is unnecessary; the papillomas go away on their own. Occasionally an unfortunate dog will have a huge number of tumors, so many that consuming food becomes a problem. Tumors can be surgically removed or frozen off cryogenically. Sometimes crushing several growths seems to stimulate the host’s immune system to assist in the tumor regression process. In humans, anti-viral doses of interferon have been used to treat severe cases of warts and this treatment is also available for severely-infected dogs. Sometimes some of the warts can be removed and made into a vaccine that is felt to stimulate the immune system to remove the tumors, though such vaccines do not seem to be as effective as one might want and currently no manufacturer is making one.

Effective therapy for viral papillomas has been elusive though recently (May 2008) a study was published by a veterinary research group in Turkey. They found that a 10-day course of the antibiotic azithromycin was able to remove all lesions within 15 days with no recurrences during an 8-month follow up period. This therapy is readily available in the U.S. and is likely to become treatment of choice.

Date Published: 9/10/2001
Date Reviewed/Revised: 04/01/2009