Do horned rabbits really exist ? - Papillomatosis
Esther van Praag Ph.D.
Warning: this file contains pictures that may be distressing for people
When legend meets science...
Between the 16th and the 18th century, illustrations show the legendary horned rabbit, a hypothetical cross between the antelope and the hare. The horned animal was studied by several naturalists, who gave it the Latin scientific name Lepus cornutus.
It is, nowadays, alleged that the "horned" head of Lepus cornatus does not relate to imagination, but to the presence of papilloma or fibroma tumors. These skin tumors develop after infection of a cell by the infectious Shope papilloma virus.
Shope papilloma virus
Shope discovered the benign papilloma virus in the USA, in cottontail rabbits (Sylvilagus sp.). It occurs as a natural disease in the midwestern USA mainly, but has also been reported elsewhere. The disease can spread to snowshoe hares (Lepus americanus), jackrabbits (Lepus californicus) and house rabbits (Oryctolagus cuniculus).
The Shope papilloma virus is a DNA virus, with properties identical to those of the papovavirus family. Initially, the virus was not believed to cause harm; later it was discovered that their presence could lead to the development of malignant tumors. Ticks, mosquitoes, and bugs seem involved in the spread of the virus. The involvement of mosquitoes is demonstrated by the fact that the papilloma develops mostly on “naked” body parts of the rabbits, e.g. ears, eyelids, nose and anus.
The tumors are generally devoid of infectious virus; yet, transmission appears possible from rabbit to rabbit.
Clinical signs and diagnosis
The Shope papilloma virus will infect and transform a follicular cell, leading to a red swollen appearance of the skin. It starts as a reddish spot on the site of infection. The first apparent signs are the formation of a circular papilloma, which may become a keratinized horny wart. They are mainly observed on eyelids, on the head or at the base of the ears.
The diagnosis for papilloma is based on the disease symptoms and will be confirmed by histopathological studies of the tumor.
Surgical excision with a wide margin is the best option to remove papilloma warts. If the tissue is not fully removed, recurrence is possible. If left untreated, the wart may regress naturally, yet, about 25% of papillomas become malignant (cancer like) and develop into squamous cell carcinoma. Metastases are prone to develop in the lymph nodes and the lungs. At an advanced stage of the disease, the kidneys and the liver become affected as well.
A further type of papilloma virus can plague the domestic rabbit: oral papilloma virus, which is distinct from the Shope papilloma virus, and is characterized by the development of tumors in the oral cavity only. The oral type will not be discussed here.
Surgical removal of the tumor is the treatment of choice. Ablative methods include the classical surgical excision, or destruction by laser, electrodissecation or liquid nitrogen.
When the papilloma is located at the anus, it is important to remove all the wart as well as tissue that attaches the wart to the rectum (peduncles) to avoid recurrence.
For detailed information on papilloma in rabbits,
by E. van Praag, A. Maurer and T. Saarony,
408 pages, 2010.
Many thanks to Ray Sedman (USA), Tiffany Adams (USA), and to Akira Yamanouchi (VEIN, Veterinary Exotic Information Network) for the permission to use their pictures.
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