Diseases in Rabits: Myxomatosis

What is Myxomatosis?

Myxomatosis, or "Myxo" as it is commonly known, is a viral disease of rabbits. The virus is called Myxoma virus and belongs to the large family known as Poxviruses.

Myxomatosis was originally discovered in the wild rabbit population of South America in 1896. These rabbits had developed immunity to the virus and as a result only showed mild signs such as small "wart-like" pox lesions on the skin. It was noted that introduced species of European rabbit were highly susceptible to the disease and in almost all cases died from the infection.

In 1950 the virus was imported to Australia in an effort to control the massive populations of rabbits following their introduction in 1859. The virus spread rapidly and resulted in approximately 95% of Australia's wild rabbit population being killed.

How common is Myxomatosis?

Each year at Karingal Veterinary Hospital between 10 and 30 rabbits are euthanased after being infected with Myxomatosis.

Which rabbits are susceptible to Myxomatosis?

All breeds of rabbits descended from the European rabbit are susceptible to Myxomatosis. This includes the wild rabbit along with all the domesticated breeds of rabbits commonly kept as pets. There is no evidence to suggest one breed is more susceptible than another is. Males and females are affected at the same rate.

What are the signs of Myxomatosis?

Once a rabbit is infected with Myxomatosis the virus first localises in the skin at the infection point for 24 hours. It rapidly multiples and by the second day the virus spreads to the lymph nodes. The virus is found in the blood, spleen and liver by the third day after infection. On the fourth day the virus can be found throughout the body. Up until this point the only visible sign of infection is a small lump at the infection site. On the fifth day post-infection the more commonly noticed signs of infection begin to develop. These include:

1. Swelling of the eyelids and conjunctiva
2. Discharge from the eyes and nose
3. Swelling of the anogenital region
4. Small burst blood vessels on the inner surface of the ears
5. High fever

These signs worsen of the next few days and death normally occurs on the tenth day after infection. The cause of death is normally bacterial pneumonia.

How is Myxomatosis spread?

By far the most common method of transmission is by blood-sucking insects. These include both mosquitoes and fleas but may include mites, lice and ticks. These insects inject the rabbit with the virus when they are feeding. It is possible for the virus to remain alive in fleas and mosquitoes for several months allowing them to infect a great number of rabbits.

Myxomatosis is accompanied by a profuse nasal and ocular discharge. There is some evidence to suggest that the virus can be transmitted by direct contact with scratches on the skin.

Do all infected rabbits die?

Not all rabbits infected with Myxomatosis will die. Recovery from the virus is rare (less than 5%) and usually involves very intensive nursing usually for several months. Even after recovery there can be severe scaling, scabbing and scarring of the head and body. It is the recommendation of Karingal Veterinary Hospital that all rabbits infected with Myxomatosis be euthanased as soon as possible to avoid undue pain and suffering.

Is there a vaccine against Myxomatosis?

There is a vaccine against Myxomatosis but it is NOT available in Australia. Federal laws prohibit the importation of the vaccine into Australia. It is feared that should the vaccine "escape" into the wild rabbit population it would result in them becoming immune to the virus.

How can the disease be prevented?

The only effective method of preventing the disease in pet rabbits is to control the insect population they may come into contact with. Some suggestions include:

1. Using fly-wire or shade-cloth over the hutch
2. Not allowing rabbits out at dusk or when mosquito numbers are likely to be at their greatest
3. Use of chemical deterrents (eg. citronella) around where rabbits are housed
4. Flea control. There is currently no flea control registered for use in rabbits but at Karingal Veterinary Hospital we recommend the use of Advantage on rabbits.
5. Ensure wild rabbits have no direct access to pet rabbits.