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 get myxomatosis.
Symptoms of Myxomatosis in Rabbits
Myxomatosis can appear with several different kinds of symptoms in pet rabbits, and is sometimes misdiagnosed as pasteurellosis, a bacterial infection which can be successfully treated with antibiotics. Rabbits may suddenly become very ill and get red, runny eyes (conjunctivitis), develop a high fever (a rectal temperature over 103 F), lose their appetite, and become lethargic. If a rabbit is showing these symptoms, it is not uncommon for it to 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 the swelling and discharge, and the fact that rabbits can only breathe through their noses, the rabbit can start to have difficulty breathing with a myxomatosis infection. Most rabbits, unfortunately, die within 14 days of the onset of these symptoms.
In more chronic cases (depending on the virus strain 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.
Causes of Myxomatosis in Rabbits
This pox virus is spread by blood-sucking insects like fleas, mosquitoes, mites, lice, and flies. It is unusual, but possible, for the virus to 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 air transmission. The rabbit flea is usually the insect to blame for myxomatosis in pet rabbits.
There is, unfortunately, no specific treatment for myxomatosis so only supportive care (fluids, antibiotics to prevent secondary infections, and pain medication) can be offered by your vet. Because domestic rabbits tend to be very susceptible to the virus and suffer while showing symptoms of the disease, euthanasia is often recommended. In some cases, however, palliative care can allow a healthy rabbit to recover.
Preventing Myxomatosis in Rabbits
The only surefire way to prevent it is to make sure no bugs or parasites can get to your rabbit. As with human diseases spread by insects, all you can do is avoid getting bug bites and going to areas where bugs and the virus are known to be.
- Avoid mosquitoes: Stay away from mosquito-infested areas and, if possible, keep your rabbit indoors.
- Use a flea preventative: A safe, monthly flea preventative like selamectin for pet rabbits (discuss this with your vet since you will need a prescription) may be a good idea even if your rabbit never goes outside. Since insects can always find a way inside, you do not want to risk your rabbit getting fleas.
- Don't let your rabbits socialize with other rabbits: Avoid fairs, shows, or any other places where rabbits are brought together (especially if an outbreak of myxomatosis is occurring in your region).
- Quarantine sick rabbits and exposed rabbits: Take steps to prevent direct transmission via your clothes, food, and other supplies and place mosquito netting over an infected rabbit's cage. Quarantine any rabbits that have been exposed to a sick rabbit for 14 days and monitor them for symptoms of myxomatosis.
- Vaccinate your rabbit: If you live in the United Kingdom, you can vaccinate your rabbit for myxomatosis. It may not entirely eradicate the disease, but it does reduce the severity of the disease and vaccinated rabbits can and do recover. The vaccine can be given to rabbits once they are 6 weeks old (immunity develops within 14 days), and repeated yearly, or every six months where myxomatosis is common. It has been available as a combination vaccine with the rabbit hemorrhagic disease vaccine since 2012.
The myxomatosis vaccine is not available in the United States or Australia; one reason for this a concern that the virus in the vaccine might spread to the wild rabbit population. If this occurred, the wild rabbit population could develop an immunity to myxomatosis, leading to an explosion in the rabbit population. In fact, myxomatosis was at one point deliberately introduced into the rabbit population in Australia to reduce the rabbit population; the outcome was an increased immunity to the disease and, in the long run, an increase in the rabbit population.