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.

Benard, 1751

Legendary horned hare, Lepus cornutus

E. T. Seton, 1937

Appearance of horned cottontails, as sketched by E. T. Seton (1937)

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.

Tiffany Adams

Wild cottontail seen in 2012 in Mankato (Minnesota, USA) with many papilloma tumors on its face, lips and neck

Shope papilloma virus

pathmicro.med.sc.edu/lecture/retro.htm

Electron micrograph of Shope papilloma viruses

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.

Ray Sedman

Typical horned papilloma growing in the inner side of the ear pinna

MediRabbit

Detail of the well-keratinized surface of a papilloma tumor located at the base of the ear of a male castrated Flemish Giant rabbit

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.

Papilloma can grow anywhere on the body, with a preference of region with little on no fur

Christine Ozouf

between the ears of a Burgundy rabbit.

Christine Ozouf

and detail of the keratinized surface of the papilloma tumor.

Arie van Praag

Older papilloma on the ears of a small harlequin rabbit.

Arie van Praag

Or the nose of the same rabbit.

Treatment

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.

Cutaneous papillomas are different from rectal papilloma. The latter is located at the anus. When their size is large, or they start bleeding, it is important to remove the entire wart as well as tissue that attach the wart to the rectum (peduncles) to avoid recurrence.

Akira Yamanouchi

Papilloma on the anus, before surgical removal

Akira Yamanouchi

Papilloma on the anus, before surgical removal

Akira Yamanouchi

Anus after laser surgery

Akira Yamanouchi

Rests of removed papilloma tumor that will be sent to a specialized laboratory for histopathological analysis

 

For detailed information on papilloma in rabbits,

Skin Diseases of Rabbits

by E. van Praag, A. Maurer and T. Saarony,

408 pages, 2010.

 

Acknowledgement

Many thanks to Ray Sedman (USA), Tiffany Adams (USA), to Christine Ozouf (FR), to Arie van Praag (CH) and to Akira Yamanouchi (VEIN, Veterinary Exotic Information Network) for the permission to use their pictures.

Further Reading

Giri I et al.1985. Genomic structure of the cottontail rabbit (Shope) papillomavirus. Proc Natl Acad Sci USA 82: 1580-1584.

Hagen KW. 1966. Spontaneous papillomatosis in domestic rabbits. Bull Wildl Dis Assoc 2: 108-110.

Kidd JG, Rous P. 1940. Cancer deriving from virus papillomas of wild rabbits under natural conditions. J Exp Med, 71: 469-493.

Kreider, J.W. and Bartlett, G.L., 1981, The Shope papilloma-carcinoma complex of rabbits: A model system of neoplastic progression and spontaneous regression, Adv. In Cancer Res., 35: 81-110.

Larson CL et al.1936. Transmission of rabbit papillomatosis by the rabbit tick, Haemaphysalis leporis-palustris. Biol Med 33: 536-538.

Phelps WC et al.1985. Shope papillomavirus transcription in benign and malignant rabbit tumors. Virology 146: 120-129.

Rous P, Beard JW. 1934. Carcinomatous change in virus-induced papillomas of the skin of the rabbit. Proc Soc Exp Biol Med 32: 578-580.

Rous P, Beard JW. 1935. The progression to carcinoma of virus-induced rabbit papilloma. J Exp Med 62: 523-548.

Seton, E.T., 1937, Lives of Game Animals, Vol. IV:787, Literary Guild of America, New York

Shope RE. 1935. Serial transmission of the virus of infectious papillomatosis in domestic rabbits. Proc Soc Exp Biol Med 32: 830-832.

Shope RE. 1937. Immunization of rabbits to infectious papillomatosis. J Exp Med 65: 607-624.

Shope RE, Hurst EW. 1933. Infectious papillomatosis of rabbits. J Exp Med 58: 607-624.

Schott, Gaspar, 1667. De Lupo, & variis ejus speciebus, Physica curiosa, Second Edition.

Syverton JT. 1952. The pathogenesis of the rabbit papilloma-to-carcinoma sequence. Ann NY Acad Sci 54: 1126-1140.

 

 

 

 

 

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