What is Head Tumors (Shope Papilloma Virus)?
Discovered in 1933 by Shope, this virus is reported mainly in North American species. Shope papilloma affects mostly wild cottontail rabbits, snowshoe hares, jackrabbits, and California brush rabbits. While it occurs more rarely in domestic rabbits, the risk of tumors becoming cancerous is three times higher in domestic breeds than in cottontails. Tumors that are cancerous, or that interfere with daily life, may need to be surgically removed. Shope papilloma is distinct from the oral papilloma virus, which causes growths inside the oral cavity.
Cottontail rabbit papilloma virus (CRPV), or the Shope Papilloma Virus, causes cancer-like growths, or papillomas, that are usually benign. While they often clear up on their own without treatment, in the rare case, their presence can lead to malignant tumors.
Symptoms of Head Tumors (Shope Papilloma Virus) in Rabbits
- Red, swollen spot at infection site
- Raised, red areas of skin that are often circular
- Wart-like growths that are rough and rounded in the early stages
- Horny growths visible on abdomen, thighs, shoulders, neck, head, ears, nose, eyes or eyelids
- Tumors that have a cauliflower-like appearance
- Tumors that bleed, especially with trauma
- Growths near anus
- Head tilt due to neck, ear or brain tumors
Note that any growths seen inside the mouth are caused by a separate and distinct virus, the oral papilloma virus. If tumors turn cancerous, and spread inside the body, secondary symptoms can include:
- Noticeable lumps and growths under the skin
- Lymph node enlargement
- Weight loss
- Difficulty breathing
- Reduced appetite
- Decrease in grooming
- Decrease in playing and activity
- Organ failure
Causes of Head Tumors (Shope Papilloma Virus) in Rabbits
The Shope Papilloma Virus is a viral disease of the papovavirus family, and it transmittable through direct contact with the virus, or through contact with a carrier of the virus. These include:
- Ingestion of material containing the virus, such as cells from tumors
- Bites from arthropods, such as ticks, mosquitoes and other bugs, that carry the virus
- Transmission possible from rabbit to rabbit
Diagnosis of Head Tumors (Shope Papilloma Virus) in Rabbits
During a physical exam, your veterinarian will most likely recognize the types of growths visible on your rabbit as those caused by the Shope Papilloma Virus. In most cases, these tumors will regress on their own, but if malignancy is suspected, or if the tumor is hindering your rabbit’s ability to eat or move, then removing the tumor may be required.
In this case, a diagnosis of the virus can be confirmed by histopathological study of the removed tumorous tissue. If malignancy is suspected, and thought to have spread within the body, a number of tests can be used to further assess your rabbit’s condition. These can include a more extensive physical exam, X-rays, CT scans, MRIs, and ultrasounds.
Treatment of Head Tumors (Shope Papilloma Virus) in Rabbits
Tumors caused by the Shope Papilloma Virus are usually not treated, and should regress on their own. In 35% of infected rabbits, lesions disappeared within six months. Regression of benign tumors can be influenced by factors such as previous infection, breed, and immunosuppression. Recovered rabbits are resistant to further infection.
However, removal of the tumors may be recommended in two cases. First, if the growths are hindering a healthy lifestyle, such as causing trouble eating, eliminating or moving, then they need to be removed to ensure your rabbit’s continued health. Removal will also be recommended if cancer is suspected. About 25% of papillomas become malignant and develop into cancerous tumors. Spread of the cancer, or metastases, can develop in the lymph nodes, lungs, liver and kidneys.
Removal of the tumors can be accomplished by surgical incision, electrodessication, laser or liquid nitrogen. Care must be taken to remove all of the affected tissue, because if it is not fully removed, tumors can reappear. Anesthesia may be administered.
Recovery of Head Tumors (Shope Papilloma Virus) in Rabbits
Recovery in untreated cases of benign papillomas is generally seen in 6-12 months, as the tumors naturally regress. In cases of surgery, post-operative care may be needed on a case by case basis. This can range from cleaning and checking on an incision, to future veterinary visits to scan for further growths. Your veterinarian will be sure to prescribe any needed at home procedures.
Since transmission of the virus can be from rabbit to rabbit, be sure to clean any and all living spaces and environments of your infected rabbit. Companion rabbits may need to have separate spaces until the tumors are clear, and you will need to watch for any signs of infection on them. Prevention of contracting the virus by means of a tick, flea or insect bite can include insect control or repellent.