Myxomatosis is caused by the myxoma virus, a type of pox virus that only affects rabbits. It was first discovered in 1896 in Uruguay and was imported to Australia in 1951 to control its large rabbit populations - initially having the desired devastating effect. The disease was illegally introduced to France in 1952 and it appeared in Britain the following year. It quickly spread to both wild and domestic rabbit populations and within a few years had spread throughout Europe. Myxomatosis has been a threat to wild and domestic rabbits ever since.

Who is at risk?

All rabbits, whether wild or domestic are at risk of myxomatosis.

How is it spread?

Myxomatosis is typically spread by blood sucking insects and in particular the rabbit flea, Spilopsyllus cuniculi. This flea is frequently found on wild rabbits and transmission in the absence of bites is unusual. All breeds of domestic rabbit can be affected, with little to suggest that one breed is more susceptible than another, and whatever the lifestyle of your rabbit there is a potential risk of this disease.

Signs and symptoms

The incubation period varies depending on the strain and its virulence and is typically at least five days. Accompanying the classic bulging eyes that most of us associate with myxomatosis, are localised swellings around the head, face, ears, lips, anus and genitalia. Severe swellings can lead to blindness and distortion around the face within a day or so of the onset of symptoms, leading to difficulty with feeding and drinking. Bacterial respiratory infection often complicates the disease resulting in a fatal pneumonia.

Progress of the disease may be slower in well cared for pet rabbits and recovery is sometimes possible with intensive care. However, myxomatosis can be a very protracted and profoundly unpleasant disease and euthanasia is generally recommended. Recovery in the wild occasionally occurs but for animals with severe signs death usually occurs about 12 days after initial infection.

Management of myxomatosis

There is no specific treatment for the virus and any treatment offered is merely supportive. Treatment is occasionally contemplated but would not usually be recommended for rabbits with the full-blown disease since affected individuals suffer dreadfully, have a low chance of survival and they remain a source of infection for other rabbits. The occasional individuals with milder disease may, however, recover with appropriate care.
Control of myxomatosis

To help prevent your rabbit from contracting myxomatosis, it is important to put various controls in place, for which there are two main methods: control of parasites and vaccination.

Flea control
Always keep a regular check on pets for any signs of fleas and consider the regular use of an insecticidal treatment from your vet. There is also evidence to suggest that mosquitoes and other biting flies may transmit myxomatosis in the UK, so nets and insect repellent can be used to combat this threat in warmer weather. Your vet will be able to advise you further on these measures, since not all products are suitable or safe for rabbits.

A dual vaccination covering both myxomatosis and rabbit haemorrhagic disease (RHD) has recently been launched in the UK and is designed to replace the older myxomatosis-only product during 2012. This new vaccine provides efficient and effective protection of rabbits against both diseases

Vaccination schedule
It is recommended that a single dose of the new vaccine is given to all rabbits over the age of five weeks and requires an annual booster to maintain protection

Strains of myxomatosis and vaccine development

Although myxomatosis is typically fatal in rabbits without immunity, there are many different strains and some are more virulent than others. As evolution has progressed and the virus adapts accordingly, the modern myxoma virus which causes the disease may not always kill rabbits quite as readily or rapidly as older strains, although the disease continues to have a very high mortality associated with it in pet rabbits. Previously vaccination in the UK used the related but non-disease causing Shope fibroma virus which was well proven in terms of safety and but also was similar enough to the myxoma virus to give useful levels of immunity. Attempts at producing inactivated (killed) myxomatosis vaccines have proved ineffective. Other approaches that have been taken abroad with mixed results have included using a weakened strain of the myxoma virus as a vaccine. The new vaccine is based on a novel approach disabling the myxoma virus in a way that renders it unable to cause disease but preserving its ability to providing effective protection not only against myxomatosis but also uniquely giving it the ability to protect against the equally serious rabbit haemorrhagic disease (also known as rabbit haemorrhagic disease or RHD)

Can rabbits contract myxomatosis after vaccination?

Vaccination can never guarantee 100% protection against any disease. However, when used as recommended in healthy rabbits, the new vaccine has been shown to be very effective at preventing this dreadful disease for a full 12 months representing significant advance over the older product. Vaccination may sometimes appear ineffective if given to rabbits already incubating the disease, or those whose response to vaccination can be impaired by underlying health problems, poor nutrition, genetic factors, severe stress and drug therapy. For these reasons it is always important to consider other steps to reduce the risk of infectious disease. These include the control of fleas and other external parasites and steps to prevent exposure to flies in hutches and runs. It is also important to avoid contact between domestic and wild rabbits and to ensure good basic husbandry and feeding to reduce the risk of potential health problems and associated stresses. Your veterinary surgeon will be able to advise on a care plan for your rabbit which can address all these issues.

In addition, control of fleas, good basic husbandry and steps to reduce stress should be undertaken to reduce the risk of myxomatosis and complement the protection afforded by vaccination.