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Myxomatosis (from the Greek μύξα (mucus), and ματώνω (to bleed)) (commonly called 'myxi') is a disease which infects rabbits. It is caused by the Myxoma virus. First observed in Uruguay in the late 1800s, it was deliberately introduced into Australia and the United Kingdom in an attempt to control rabbit infestation and population there; see rabbits in Australia.
Additional recommended knowledge
Effects of the disease
In rabbits of the genus Sylvilagus (cottontail rabbits), myxomatosis only causes localized skin tumors, but the European rabbit (Oryctolagus cuniculus) is more severely affected. At first, normally the disease is visible by lumps (myxomata) and puffiness around the head and genitals. It then may progress to acute conjunctivitis and possibly blindness; however, this also may be the first indication of the disease. The rabbits become listless, lose appetite, and develop a fever. Secondary bacterial infections occur in most cases which cause pneumonia and purulent inflammation of the lumps. In typical cases where the rabbit has no resistance, death takes an average of 13 days.
Spread of the disease
After its discovery in 1896 in imported rabbits in Uruguay, a relatively harmless strain spread quickly throughout the wild population in South America.
In Australia, the virus was first field-tested for population control in 1938. A full-scale release was performed in 1950. It was devastatingly effective, reducing the estimated rabbit population from 600 million to 100 million in two years. However, the rabbits remaining alive were those least affected by the disease. Genetic resistance to myxomatosis was observed soon after the first release and most rabbits acquired partial immunity in the first two decades. Resistance has been increasing slowly since the 1970s, and the disease now only kills about 50% of infected rabbits. In an attempt to increase that number, a second virus (rabbit calicivirus) was introduced into the rabbit population in 1996.
Myxomatosis was unintentionally introduced to France by the bacteriologist Dr. Paul Armand Delille, following his use of the virus to rid his private estate of rabbits in June 1952 (controversially, he inoculated two of the rabbits on his land). Within four months the virus had spread 50 km; Armand suspected this was due to poachers taking infected rabbits from his estate. By 1954, 90% of the wild rabbits in France were dead. The disease spread throughout Europe. It reached the UK in 1953, apparently without human action. Some in the UK deliberately spread the disease, placing sick rabbits in burrows, while many others deplored the cruelty and suffering. The government refused to legislate to make deliberate spread of the disease illegal. By 1955, about 95% of rabbits in the UK were dead. Rabbits suffering in the last stages of the disease, commonly called "mixy" or "myxie" rabbits, are still a common sight in the UK in 2007. Unfortunately, the disease affects more than the rabbits: the Spanish lynx among others is now almost extinct because the declining rabbit population, encompassing 90% of its diet, has caused mass starvation. It is not uncommon for shooters to specifically target infected rabbits, viewing the act as being merciful.
Use of vaccine
A vaccine is available for pet rabbits, but is illegal in Australia because of fears that the immunity conferred by the vaccine could be transmitted through the wild rabbit population, because the vaccine uses a live virus, the Shope fibroma virus.
The development of resistance to the disease seems to have taken different courses. In Australia, the virus initially killed rabbits very quickly, about 4 days after infection. This gives little time for the infection to spread. As a result of this, a less virulent form of the virus has become prevalent there, spreading more effectively by being less lethal. In Europe, rabbits which are genetically resistant to the original virus have spread. It is conjectured that this is because the main transmission vector in Australia is the mosquito, while in Europe it is the rabbit flea.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Myxomatosis". A list of authors is available in Wikipedia.|