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General information
Myxoma virus is the causative agent of myxomatosis in rabbits. It is a large, enveloped DNA virus and belongs to the genus Leporipoxvirus (family: Poxviridae). Despite its envelope, poxviruses are relatively stable in the outside world. However, inactivation can easily be achieved with ordinary disinfectants.
The virus is very host-specific: The European rabbit and domestic rabbit breeds descending from it are most susceptible, but American rabbit species and European hare species can be infected as well. The virus is mainly transmitted through insects (gnats, fleas – mechanical transmission), thus, the disease primarily occurs between the end of July and October. Transmission by direct contact is usually only important in cases of high population density.
After a primary virus replication in the mucous membranes of the head, the regional lymph nodes become infected. Subsequently, there is a cell-associated viraemia (lymphocytes) and the virus spreads to nearly all organs.
After an incubation time of 4 to 10 days, an infection with myxoma virus causes an acute systemic disease with severe conjunctivitis and hypodermal oedema (especially in the facial and the anogenital region). Nodular tumours in the skin and subcutaneous tissue may also occur. Respiratory problems and dysphagia result in inappetence and anorexia. The mortality rate is between 25 and 90%. Chances of full recovery are generally very low. Seriously affected animals should be euthanised.
Due to the high mortality rate caused by the disease, the virus was introduced into rabbit populations in Europe, Chile and Australia around 1950 for population control. It has since been endemic in these countries. However, co-evolution of the virus and the rabbits has led to weakened virus strains and virus-resistant rabbits. Thus, the severity of clinical symptoms strongly depends on the virulence of the present virus strain and the susceptibility of the host.
Vaccines are available for prophylaxis.