Myxomatosis (sometimes referred to as myxi) is caused by the myxoma virus. This virus is a kind of pox virus that only affects rabbits. There are also different strains of this pox virus which vary in their virulence (basically the ability to cause disease), but both wild and domesticated rabbits can contract myxomatosis.
Myxomatosis can exhibit several different kinds of symptoms in pet rabbits.
Rabbits may suddenly become very ill and display conjunctivitis (red, runny eyes), develop a high fever (a rectal temperature of over 103 degrees Fahrenheit), lose their appetite, become lethargic, and may die within 48 hours. Sometimes the illness lasts longer and the mucous membranes and other tissues, including the eyes, nose, mouth, ears (which become droopy if they are usually standing), genitals, and anal areas, become swollen. The entire face may also become very swollen and thick pus may be discharged from the nose. Due to all the swelling and discharge, and the fact that rabbits can only breathe through their noses, the rabbit may have difficulty breathing with a myxomatosis infection. Most rabbits, unfortunately, die within 14 days of the onset of symptoms.
In more chronic cases (and depending on the strain of the virus and immunity of the rabbit), lumps and nodules (myxomas) may develop on the body.
Rabbits with this lumpy form of myxomatosis may survive and become immune to the myxomatosis virus. This is commonly seen in wild cottontail rabbits but unfortunately seems to be a less likely course of the disease in domestic rabbits (Oryctolagus cuniculus). Instead, most pet rabbits that are diagnosed with myxomatosis end up suffering from the acute forms of the disease and eventually die.
How is Myxomatosis Spread to Rabbits?
The pox virus that is myxomatosis is spread by blood-sucking insects (fleas, mosquitoes, mites, lice, and flies) in most cases. It is unusual, but possible, that the virus can also spread by direct contact between rabbits, indirect contact (via items such as food dishes or clothes that carry the virus from rabbit to rabbit), and by aerosols. The rabbit flea is usually the insect to blame for myxomatosis in pet rabbits.
Treatment of Myxomatosis
There is, unfortunately, no specific treatment for myxomatosis so only supportive care (fluids, antibiotics to prevent secondary infections, pain medication, etc.) can be offered by your exotics vet. Because domestic rabbits tend to be very susceptible to the virus and suffer while showing symptoms of the disease, euthanasia is often recommended.
Preventing Myxomatosis in Your Rabbit
- Keep your rabbit indoors and away from mosquito-infested areas.
- Use a monthly safe flea preventative like selamectin for pet rabbits (discuss this with your exotics vet since you will need a prescription) even if your rabbit never goes outside. Remember, insects can get in your house, so your rabbit doesn't need to leave it to get fleas.
- Don't take rabbits to fairs, shows, or any other places where rabbits are brought together while an outbreak of myxomatosis is occurring.
- Quarantine sick rabbits and take steps to prevent direct transmission via your clothes, food, and other supplies. Place mosquito netting over the infected rabbit's cage as part of the quarantine process.
- Quarantine any rabbits that have been exposed to a sick rabbit for 14 days and monitor them for symptoms of myxomatosis.
- Vaccinate your rabbit for myxomatosis if you live in the United Kingdom. The vaccine may not completely prevent myxomatosis, but it does reduce the severity of the disease and vaccinated rabbits recover. The vaccine can be given to rabbits once they are six weeks old (immunity develops within 14 days), and repeated yearly, or every six months where myxomatosis is common. It has been a combination vaccine with the rabbit hemorrhagic disease vaccine since 2012.