Italian microbiologist Sanarelli first reported myxomatosis in 1896, when a laboratory rabbit colony he had imported into Uruguay for public health research suddenly died of an extremely infectious disease. The virus was identified in the 1930s and has subsequently been used in the biological control of rabbit populations in Australia and France in the 1950s. It spread from France to the UK in 1953 where it decimated the European wild rabbit population and is now widespread both in wild and domestic rabbits in the UK.
Myxomatosis is an infectious disease caused by the myxoma virus which is spread by biting flies or fleas and by mechanical vectors such as non-biting insects, bedding and food. The virus causes cells of the epidermis (the outermost layer of the skin) to die, and an accumulation of fluid beneath the dermis (the layer of skin below the epidermis).
The virus is usually introduced by biting insects, which causes local skin trauma, the introduction of the virus into the bloodstream and multiple skin eruptions (a rash).
Myxomatosis is widespread throughout the UK and has a higher seasonal prevalence in late summer, autumn and early winter. Both sexes and all breeds of rabbit can be affected with myxomatosis.
The main form of transmission is via insects like the rabbit flea (Spilopsyllus cuniculi) and mosquitoes. Dog and cat fleas can also carry the virus. The virus is also found in discharges, and transmission by mechanical vectors such as non-biting insects, bedding and food also occurs.
The virus can remain in the blood of the insect for many months and the ability of the bacteria to cause the disease can vary from year to year.
Signs of disease usually show within 8 days of transmission and the duration of illness usually lasts between 11 and 18 days. Death usually occurs within 14 days of infection from an overwhelming bacterial infection or acute respiratory infection.
The most obvious signs of infection are swelling of the lips, eyelids and genitals; infected rabbits can also suffer from a high temperature (pyrexia), depression, localised skin nodules (lumps) and noisy, laboured breathing.
There are two forms of myxomatosis, acute (sudden onset) and chronic (long-term).
- Initially your rabbit will appear bright but may develop swelling around the lips, eyelids and genitals.
- Your rabbit may become lethargic and develop a temperature with swollen eyelids causing blindness, but will still try to eat and can be hand fed.
- Because rabbits breathe through their nose swelling of the nose can lead to suffocation.
- These in turn may lead to lung infection and death.
- Your rabbit will develop skin swellings, called myxomas or ‘pseudotumours’, which develop after 10-15 days, mainly on the ears, nose and paws.
- The swellings, which heal to leave scabs, soon disappear.
- 50% of rabbits can survive this form of myxomatosis so this is the form that can be treated.
Wild rabbits tend not to survive as long as domestic rabbits, as blindness and debility make them susceptible to predation from foxes and road accidents. Pet rabbits however, can survive longer with nursing care, but are usually put to sleep on humane grounds to prevent unnecessary suffering.
Fifty percent of rabbits usually survive the chronic nodular form; those affected with the chronic form may survive following infection; but the acute form is fatal and affected rabbits usually die within 2 weeks. Vaccinated rabbits can also be affected but show less severe signs and are more often than not possible to nurse through the disease, although nursing care can be intensive and take many weeks if not months.
Medical treatment usually involves eye drops, antibiotics and gastrointestinal stimulants, with hand-feeding/syringe feeding, as well as general nursing to keep the rabbit clean, dry and warm.
Myxomatosis is very common in wild rabbits but is also seen in pet rabbits, so make sure your rabbits hutch isn’t sited near wild rabbit populations. If you are unsure of the status of wild rabbits in your area, contact your local farmer, as they are often able to give an indication of current disease in a geographical area.
The virus is resistant to dryness and cold but not to heat and light, so the use of disinfectants such as bleach or caustic soda is extremely beneficial, although ensure that your rabbit’s hutch is thoroughly dry before returning your rabbit to it and bowls, bottles, etc are rinsed before using them again.
A combined vaccination is available for myxomatosis which also vaccinates against viral haemorrhagic disease 1 (VHD1). Immunity develops within 21 days of vaccination; your vet will examine your rabbit to ensure they are healthy at the time of vaccination, since rabbits already fighting illness may not respond to vaccination.
Vaccination can be started at 5 weeks of age and is best given in May or June before the peak myxomatosis season in late summer and autumn. The vaccine is not recommended in pregnant does or bucks used for breeding. An annual booster is sufficient to protect against both myxomatosis and VHD1. Your rabbit will require a separate vaccination to protect against VHD2.
If you live in a high-risk area, also consider hanging insect repellent strips and mosquito netting over your rabbit’s hutch to prevent him coming into contact with myxomatosis vectors. You should also ensure that your rabbits bedding is kept clean and dry, to avoid attracting unwanted insects.
Make sure your garden is not accessible to wild rabbits; this will prevent your rabbit coming into contact with wild rabbits that may be carrying the disease.
If you have other pets that come into contact with your rabbit, such as dogs or cats, make sure they are also regularly treated for fleas with products available from your veterinary surgery.