This viral disease of New World rabbits is transmitted by mosquitoes, black flies, fleas, lice, and mites. The virus adheres to the mouthparts of the arthropods as they probe the epidermis. Once the mouthparts are contaminated, the virus can be inoculated into another host during a later probe. The virus does not replicate in the vector. The natural hosts of the myxoma virus are the jungle rabbit, Sylvilagus brasiliensis , in South and Central America and S. bachmani in California, USA. It has only mild effects on New World rabbits, causing cutaneous fi broma (relatively harmless wart - like skin blemishes) but not a systemic disease. However, the myxoma virus is quite deadly to Old World rabbits, Oryctolagus spp. Infected European rabbits display a bedraggled appearance, with partially or completely swollen eyelids, discharge from the conjunctiva and nose, and swollen ears and head. Nodules measuring up to 1 cm in diameter may be found anywhere on the body. In addition to being almost blind, affected animals frequently are in respiratory distress.
In 1950, myxoma virus was introduced to Australia to reduce the population of European rabbits that had been deliberately but regrettably introduced, and where they had few natural enemies. The rabbits in Australia have caused the extinction of numerous animals and plants, and caused extensive soil erosion due to overgrazing. The virus quickly reduced the population of rabbits from 600 million to 100 million, but the rabbit populations have recovered partly as disease resistance has developed. Recently another virus, rabbit calicivirus, has been introduced to attempt population suppression in Australia. Myxomatosis was also introduced to France, where it spread rapidly throughout Europe, causing significant decreases in rabbit populations, and populations of some of the predators that fed upon them. Overall, the reduction in rabbit abundance is estimated at 30% – 40% in Australia to 50% – 70% in Great Britain. Vaccine is used in Europe to provide protection of rabbits from the virus; both live attenuated virus vaccines and inoculation with rabbit fibroma virus (which is innocuous to European rabbits) are used. In many respects, rabbit fibroma virus can generally be considered the eastern North American equivalent of myxoma virus, and is often seen in eastern cottontails, Sylvilagus floridanus , but with few serious effects.
