Do horned rabbits really exist ?
Fibroma growths
Esther van Praag Ph.D.
Warning: this file contains
pictures that may be distressing for people
Between the 16th and the 18th century,
illustrations show the legendary horned rabbit, a hypothetical cross between
the antelope and the hare. Several naturalists studied the horned hare and
gave it the Latin scientific name of Lepus cornutus.
It was popularly called raurackl, or "stag-hare.
It is, nowadays, alleged that the "horns"
around the head of the "Lepus cornatus"
do not relate to imagination, but to the growth of papilloma or fibroma tumors.
The latter develop after infection of a cell with the Shope papilloma virus,
Shope fibroma virus or the leporipoxvirus.
Shope fibroma virusThe Shope fibroma virus was discovered in 1931 by R.E.
Shope. It is found mainly on the US continent, among the cottontail (Sylvilagus
floridanus) population. It was soon realized
that the virus is transmissible between cottontails and rabbits. A viral
infection results in the development of gross and microscopic lesions called fibromas.
The virus is spread through bites of blood seeking insect
(e.g. fleas, mosquitoes). Once a cutaneous cell is infested, it will undergo
a transformation leading to the formation of a tumor.
Shope showed by different experimental techniques that
the fibroma virus is related to the myxoma virus. This property is nowadays
exploited by using the live Shope fibroma virus to vaccinate against myxomatosis.
European hares are known to carry a virus (Leporipoxvirus)
responsible for fibromatous diseases. Rabbits are susceptible
to this virus. Clinical signs include the growth of numerous skin nodules (up
to 2.5 cm in size) on the face, eyelids and around the ears. The transmission
mode of this virus is unknown. Clinical signs and diagnosis
The symptoms of fibromatosis were accurately described by
Shope in 1931, with tumors appearing essentially on the feet and limbs, and
to a lesser extent on the face, the nose, the eyelids, and the back. In
newborn rabbits and cottontails, it causes general and severe diseases; in adult
rabbits, the tumors often regress naturally. This virus is, furthermore,
known to cause a variety of tumors in cattle.
This disease not frequently found in pet rabbits. The
first signs of infection are the thickening of subcutaneous tissues. A soft
well-outlined swelling will grow slowly, and can develop into a large tumor,
with a diameter of 7 cm, and a thickness of 2 cm. The large size leads to
disturbances in the daily activities, such as movement and search for food.
The tumor consists mainly of connective tissue.
Subcutaneous tumors can lead to compression and damage of the underlying
tissues such muscles and tendons. In rare cases, it was observed that the
tumor invades the muscle tissue.
Generally, the tumors regress spontaneously after 10 to
14 months.
Fibroma tumors must be differentiated from myxoma and
papilloma tumors. The appearance of the fibroma is usually flat and it is
located in the subcutaneous tissues, while the papilloma tumors have the
aspect of a wart, with a well-keratinized surface.
The diagnosis is based on clinical signs and can be
confirmed with a biopsy sample. Histopathological examination of the skin
lesions shows intracytoplasmic inclusion bodies.
A virus called "malignant rabbit fibroma virus"
has been isolated in rabbits. It can lead to fibrosarcoma. As it presents
antigenic similarities with the fibroma and myxoma viruses, it is thought to
be a recombinant of both viruses, but this is not yet well defined. The
presence of this virus is accompanied by immunodepression, malignant tumors
and infections.
Fibrosarcoma often start in the soft tissue and spread to
a bone by direct invasion or transport of a metastatic cell via the blood
circulation. Secondary fibrosarcoma may develop in lungs, heart, kidneys and
lymph nodes.
Treatment
Surgical
removal is not recommended, because recurrence is quick and usually more extensive.
If excision becomes necessary, it must be wide. For
more details, see: Fibrosarcoma in rabbits. For detailed
information on fibrosarcoma in rabbits, by
E. van Praag, A. Maurer and T. Saarony, 408
pages, 2010.
AcknowledgementThanks are due to Jeff Hymel and to Akira Yamanouchi (Veterinary Exotic Information
Network), for
the permission to use their pictures. Further Reading
Hu J, Cladel NM, Pickel MD,
Christensen ND. Amino acid residues in the carboxy-terminal
region of cottontail rabbit papillomavirus E6
influence spontaneous regression of cutaneous papillomas. J Virol. 2002; 76(23):11801-8. Singh SB, Smith JW, Rawls WE, Tevethia
SS. Demonstration of cytotoxic antibodies in
rabbits bearing tumors induced by Shope fibroma virus. Infect Immun. 1972;
5(3):352-8. Smith JW, Tevethia SS, Levy BM, Rawls
WE. Comparative studies on host responses to Shope fibroma virus in adult and
newborn rabbits. J Natl Cancer Inst. 1973;
50(6):1529-39. Friedman-Kien AE, Fondak
AA, Klein RJ. Phosphonoacetic acid treatment of shope fibroma and vaccinia
virus skin infections in rabbits. J Invest Dermatol.
1976; 66(02):99-102. Block W, Upton C, McFadden G. Tumorigenic
poxviruses: genomic organization of malignant rabbit virus, a recombinant
between Shope fibroma virus and myxoma virus. Virology. 1985; 140(1):113-24. Strayer
DS, Cabirac G, Sell S, Leibowitz
JL. Malignant rabbit fibroma virus: observations on the culture and histopathologic characteristics of a new virus-induced
rabbit tumor. J Natl Cancer Inst. 1983; 71(1):91-104. Strayer
DS, Sell S. Immunohistology of malignant rabbit
fibroma virus--a comparative study with rabbit myxoma virus. J Natl Cancer Inst. 1983; 71(1):105-16. Strayer
DS, Skaletsky E, Cabirac
GF, Sharp PA, Corbeil LB, Sell S, Leibowitz JL. Malignant rabbit fibroma virus causes
secondary immunosuppression in rabbits. J Immunol. 1983; 130(1):399-404. Strayer DS, Skaletsky E, Leibowitz JL, Dombrowski J.
Growth of malignant rabbit fibroma virus in lymphoid cells. Virology. 1987;
58(1):147-57. |
||||||||
e-mail: info@medirabbit.com
