SHOPE FIBROMA
Fibrous tumours or fibromas caused by a virus and occurring in the skin of cottontails were first described by Shope in 1932. In Ontario, cottontails are commonly afflicted with Shope fibromas. The causative virus is transmitted from cottontail to cottontail by mosquitoes, fleas and possibly other biting insects.
The tumours are firm, pinkish-red, usually spherical masses. One or several may be present in the skin of an animal. In cottontails examined from Ontario, the lesions have usually been confined to the legs and face and have been observed most frequently during late summer, autumn and winter.
Shope fibromas will disappear, presumably following the development of immunity. A naturally occurring fibroma has been known to remain on a cottontail for as long as 10 months.
This disease may reach epizootic proportions in a cottontail population but it does not appear to be a mortality factor. There is no evidence to suggest that fibromas are responsible for declines in cottontail populations.
Present knowledge indicates that the virus causing the Shope fibroma is not transmissible to man either by handling or by eating affected carcasses. Furthermore, as fibromas are confined to the skin, they are removed when the animal is pelted. The carcass of an affected cottontail is considered safe for human consumption.
Tumours similar to Shope fibromas are present in gray squirrels in Ontario.
Selected References:
Herman, C.M., L. Kilham and 0. Warbach. 1956. Incidence of Shope's rabbit fibroma in cottontails at the Patuxent Research Refuge. J. Wildl. Manage. 20:85-89.
Kilham, L. and H.T. Dalmat. 1955. Host-virus-mosquito relations of Shope fibromas in cottontail rabbits. Amer. J. Hyg. 61:45-54.
Kilham, L., C.M. Herman and E.R. Fisher. 1953. Naturally occurring fibromas of grey squirrels related to Shope's rabbit fibroma. Proc. Soc. Exp. Biol. Med. 82:298-301.
Shope, R.E. 1932. A transmissible tumor-like condition in rabbits. J. Exp. Med. 56:793-802.
