Papillomatosis in Rabbits

CRPV is commonly a benign, natural disease of wild cottontail rabbits, which gives it its name. It can occur in domestic rabbits, where there is a chance that the tumors can become cancerous. The horny growths that often occur on the neck, shoulders and head gave rise to the tales of the legendary horned rabbit in previous centuries.

There are two kinds of infectious viruses in rabbits that cause papillomatosis, cottontail rabbit papilloma (CRPV) and oral papilloma. CRPV causes horny wart like skin growths, while in oral papilloma, small nodules develop on the tongue and mouth. While both conditions are usually benign, and can regress without treatment, there are cases when intervention may be necessary.

Symptoms can vary between the two types of papillomatosis, and include:

CRPV

• Horny warts that appear on the abdomen, anus, neck, shoulders, ears, nose, and eyelids
• Lesions on ears and eyelids, that are rounded and rough
• Red, swollen, circular formations on the skin
• Tumors with a cauliflower like appearance
• Head tilt due to tumors

Oral papillomatosis

• Oral discomfort
• White or gray nodules or warts in the mouth or on the tongue

If the tumors turn malignant, secondary symptoms associated with CRPV can include:

• Lymph node enlargement
• Anorexia
• Lethargy
• Diarrhea
• Weight loss
• Weakness
• Pain
• Decrease in grooming, playing and activity

Types 

Cottontail rabbit papilloma virus (CRPV) -  This is also called Shope papilloma virus, and causes skin tumors and warts. These tumors are never present in the oral cavity or mucous membranes. This papovavirus was discovered by Shope in 1933. These tumors can turn malignant.

Rabbit oral papilloma - This distinct papovavirus infection often occurs in rabbits between 2 and 24 months of age. Tumors appear as whitish nodules only in the oral cavity, usually on the tongue, and are not highly contagious. The virus may stay dormant in the mouth until trauma occurs. No malignancy has been reported with these tumors. It is not related to CRPV.

The cause of both types of papillomatosis in rabbits is exposure to one of two distinct DNA papovaviruses. These viruses can be contracted through:

• Bites from ticks, mosquitoes and other bugs
• Transmission from rabbit to rabbit, including mother to offspring
• Direct contact of virus, such as through ingestion

Diagnosis is based on the appearance of the growths, locations of the growths, and histopathologic studies of the tumors. Tissue samples will be examined for the type of tumor, and presence of malignancy. The distinction can be made between the two types of papillomatosis from these observations, as CRPV has horny wart like growths in the skin that are never present in the mouth, while oral papillomatosis only appears as nodules in the mouth.

If tumors are suspected to be malignant, further tests can be performed to assess how far the cancer has spread. The cancer can spread into the lungs and lymph nodes, and can progress at an advanced stage into the kidneys and liver. Further testing can include physical exams, CT scans, X-rays, MRIs, and ultrasounds.

In both cases of CRPV and oral papillomatosis, treatment is usually not prescribed as most growths will regress on their own over time. There are situations which may require removal of the tumors or nodules.

CRPV

In cases where tumors become malignant, are located near the anus, or if the tumors are stopping your rabbit from living a healthy life, surgery may be recommended. About 25% of tumors from CRPV can develop into squamous cell carcinoma. Surgical removal is often recommended, being sure to remove the growth in its entirety, or else it may return. Growths can also be removed by laser, electrodessication or liquid nitrogen. 

Oral Papillomatosis

Mouth and tongue nodules characteristic of this type of papillomatosis usually resolve within a few weeks, and often cause very little inconvenience for your rabbit. Treatment or removal is typically not needed. Larger nodules may cause issues during dental work. Surgical removal may only be necessary in some cases where the nodules are interfering with your rabbit’s health or eating habits.

If surgery to remove growths was performed, your veterinarian will discuss with you any post-operative care your rabbit may need. If no treatment was given, then you will most likely see the growths or nodules regress over time. Avoid contraction of the papillomatosis viruses by using tick and insect control, or by keeping your rabbit away from tick or insect ridden areas.