Myxomatosis in Rabbits

Myxomatosis

This disease is caused by a Myxoma virus that belongs to the family of pox viruses. The virus originates from South America where it causes a mild disease in the wild rabbit population. However when European rabbits were imported to South America the infection with the myxoma virus resulted in almost 100% mortality of the European rabbits. The European rabbit had been introduced to Australia by early colonists but by the 1950’s the rabbit population was out of control. In an attempt to reduce rabbit numbers the myxoma virus was intentionally introduced to Australia. By accident the virus was also introduced into Europe decimating the wild rabbit population.

The disease occurs in both domestic and wild rabbits but rarely in European hares that seem to have some resistance. The myxoma virus is spread by direct or indirect contact but most often by parasitic vectors. In Europe the rabbit flea and mosquito are the most important methods of spreading the virus. The virus can survive for several months in over wintering rabbit fleas and mosquitoes.

Symptoms

When the Myxoma virus originally infected unexposed European rabbits it produced an acute illness that resulted in 100% mortality. After infection, skin lesions appeared on the 3^rd day and had spread every where by the 4^th day. The skin lesions are typically swelling of the genitals and of the head, especially the eyelids which results in blindness. The rabbit’s appetite remains normal until shortly before death which is on average 13 days after infection.

In time rabbits developed some immunity to the myxoma virus and the disease process changed in some cases to produce chronic form of Myxomatosis. In this chronic nodular form of Myxomatosis swellings called pseudotumours develop 10-15 days after infection. These lumps are mainly seen on the ears, nose and paws. The lumps or pseudotumours can spontaneously regress leaving scabs which later disappear. Mortality in the chronic nodular form is about 50% with an average survival time of 40days. Chronic Myxomatosis and Spirochaetosis (Rabbit Syphilis) can look very similar but spirochaetosis is extremely rare.

There are other forms of the disease that result in respiratory symptoms that can be very difficult to differentiate from other causes of pneumonia such as pasturellae.

Treatment

Treatment of rabbits suffering with the acute form of the disease is disappointing. Even with excellent nursing from an attentive owner who manages to keep the affected rabbit eating and drinking they often die of breathing complications after 2 weeks. Thus it is more humane to euthanase them once the diagnosis of the acute disease has been made.

Rabbits affected by the chronic nodular form have a 50% chance of the lesions regressing and then survival. In such cases good nursing and the use of antibiotics to control secondary infection may be beneficial.

Control

To control the spread of the disease it is important to do two things:

Disinfect the area where the affected rabbit was to kill the virus.

Control rabbit fleas and mosquitoes that can spread the virus.

Care must be taken that the disinfectant used is not harmful to rabbits.

The use of the cat flea control product AdvantageŽ can be useful in controlling rabbit fleas and mosquitoes on rabbits.

Prevention

As there is no effective treatment for so many viral diseases in animals, prevention by vaccination is the best policy. There are many different types of vaccine strategies to control the disease. The most commonly use vaccines consisting of a living virus that dose not cause disease in rabbits but induces cross immunity with the myxoma virus. The virus usually used is the Shope’s fibroma virus which is the active constituent of the Nobivac MyxoŽ vaccine. This vaccine can be given to rabbits as young as 6 week old and produces immunity 14d after vaccination. Normally rabbits are revaccinated annually but if there is a high risk of infection then revaccination every 6 months is advisable. Vaccinations should not be given within 14 days of viral haemorrhagic disease vaccinations.