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• Acupuncture PETS GALLERY Myomatosis and VHD are commonly vaccinated against in pet rabbits |
Myxomatosis
Myxomatosis is a viral disease which decimated the wild rabbit population when it arrived in Britain 40 years ago. The number and severity of outbreaks varies over time: the myxomatosis virus is notorious for its ability to mutate from year to year, and the background immunity in the wild rabbit population also varies. Britain - particularly southern areas (the south west, Hampshire, Suffolk, Cambridgeshire) suffered a severe outbreak of myxomatosis in autumn 2000, which was thought to have been caused by a more virulent strain than had occurred in recent years. A handful of reports of vaccinated rabbits developing myxi in these areas led to a suspicion that vaccination may not be fully effective against this possible new strain of myxomatosis and served as a reminder to all rabbit owners that vaccination is just one of a series of measures that have to be taken to protect pet rabbits from this deadly disease. Is your rabbit vaccinated? Domestic rabbits do not have any genetically based immunity against myxomatosis. If an unvaccinated pet rabbit catches myxomatosis, it will almost certainly die. Pet rabbits at greatest risk are those which live outside, in contact with wild rabbits or hares, or affected by rabbit fleas - so rabbit owners who also have a dog or cat that hunts wild rabbits must be particularly careful. However, myxi can also be spread by mosquitoes, so any standing or stagnant pools of water where mosquitoes may breed should be removed. The virus can survive in overwintering fleas and mosquitoes sheltering in hay and in houses. It can also be spread by Cheyletiella fur mites, Houserabbits are at less risk than outdoor rabbits, but can and do get myxomatosis. They must be vaccinated and protected from possible sources of myxomatosis transmission too. How is it spread? Myxi is usually spread by biting insects (fleas, mosquitoes) carrying the virus. However, direct rabbit-to-rabbit spread can occur. Previously this was mainly seen in a French respiratory strain of the disease, but recent reports suggest that rabbit to rabbit spread may be occurring in the recent (autumn 2000) outbreak in the UK that led to many deaths in wild rabbits and some deaths in pet rabbits. What happens when a rabbit catches myxomatosis? The disease starts with runny eyes and swollen genitalia. If full blown myxi then develops, the rabbit will be a pitiful sight. Severe conjunctivitis causes blindness and is accompanied by swelling of the head and genital region, plus lumps on the body. The rabbit can take a fortnight to die and treatment of this "classic" form of myxomatosis is usually futile. There are also two atypical forms of myxomatosis: one causes pneumonia and a snuffles-like illness; the other ("Nodular myxomatosis") mainly affects skin and carries a better prognosis. If a vaccinated rabbits does develop myxomatosis, the disease tends to be much less severe. The exact pattern of disease seen in vaccinated animals is very variable, and impossible to predict: it depends upon how much immunity the rabbit has. Some rabbits develop just a few odd skin lesions and remain otherwise well; others become quite poorly and suffer from swellings and conjunctivitis more like classical myxomatosis. What about myxomatosis vaccination? Vaccination is a vital part of a package of measures you can take to protect your rabbit and the RWA urges all rabbit owners to make sure their rabbit is vaccinated and boosters are kept up to date. The myxomatosis vaccine in the Britain (Nobi-vac Myxo) is made from a harmless virus called Shope Fibroma. Antibodies made in response to Shope Fibroma also protect against myxomatosis - this is called cross immunity. It's just the same principal that Jenner discovered when he used cowpox to vaccinate against smallpox when vaccination was first discovered. Different vaccines (including live attenuated myxomatosis virus) are used elsewhere in Europe, but tend to have more side effects and there are concerns that they are not safe enough for use in pet rabbits. Until autumn 2000, annual boosters were thought to be adequate in most areas of the UK, with six-monthly boosters in high risk areas. However, during the autumn 2000 outbreak there was a possibility that a new strain of myxomatosis virus was circulating, against which the vaccine may have been partially effective. Hence, vaccine manufacturers, Intervet, recommended for a time that rabbits in all areas of the UK should be vaccinated at six-monthly intervals. At the time of writing (early 2002), Intervet have resumed their previous recommendation of six monhtly boosters for rabbits in high risk areas and twelve mothly boosters for everyone else!Because Myxi tends to break out in autumn, the optimal time for once-yearly vaccination is late Spring/early summer. "High risk" areas typically include any low-lying areas (e.g. East Englia; vale of York) plus anywhere with standing water; a large mosquito population; or local outbreaks of myxi in wild rabbits. If you hear of a myxi outbreak in your vicinity, it would be wise to ensure your bunny has been vaccinated within the previous 6 months. Additional precautions Even if your rabbit is vaccinated, you must also take steps to prevent biting insects getting to your rabbit. For example, try to buy hay from farms free of myxomatosis; fit insect screens to outdoor hutches and runs; eliminate standing water from your garden where mosquitoes could breed. be especially careful if you have a dog or cat that hunts wild rabbits, as they could bring rabbit fleas home on their noses! You also need to make sure that rabbits living outdoors cannot make contact with wild rabbits or hares. Special points about the myxi vaccine Most vaccines are given entirely subcutaneously, but the myxi vaccine is different. About a tenth of the dose must be given intradermally - into the layers of the skin - for adequate immunity to be achieved. This is tricky - some people give it into the thicker skin at the base of the ear; others on the way in or out of the scruff; but is absolutely vital to ensure the correct "antigen presentation" and to stimulate an immune response in the skin which is of course where the myxomatosis virus usually gains entry to the rabbit. If you are involved with a rescue centre where the vet allows lay personnel to vaccinate the rabbits, please double check the correct technique is being used. If your own rabbit is being vaccinated, double check that the vet remembers the intradermal bit! Intervet need to know about any cases where vaccinated rabbits develop myxi. Your vet should liase with them to ensure they are fully briefed about the nature and severity of disease suffered by the affected animal. Can rabbits with myxomatosis be treated? If an unvaccinated rabbit catches myxomatosis and develops the full-blown classic form of the disease, survival is very unusual, even when treated with antibiotics to prevent secondary bacterial infection. Most affected pets in this situation are put to sleep to prevent further suffering. If a vaccinated rabbit is unlucky enough to catch myxomatosis, the situation is much less gloomy. How severely any one vaccinated rabbit will be affected is impossible to predict. It depends on how much immunity they developed after their vaccination. Some rabbits simply develop a single skin lump and remain perfectly well. A few become really poorly. Others fall somewhere in between, such as being a bit "off colour" with a few skin lesions. Treatment is usually successful in the vaccinated rabbit with a good vet, nursing care and a bit of luck. But it is important to realise from the outset that if the rabbit is unlucky enough to be badly affected, intensive and prolonged veterinary and nursing care (weeks rather than days) may be required. Rabbits being treated for myxomatosis need: * Careful nursing care in a warm environment (21-22 degrees centigrade) This doesn't make vaccination a waste of time - far from it. Rabbits that have not been vaccinated will almost certainly die if they catch myxomatosis.... rabbits that have been vaccinated usually live to tell the tale if they catch it. If you know anyone with a pet rabbit, please do tell them about the importance of vaccination against both VHD and myxomatosis, as well as insect proofing measures.
This article was written specifically for the BHRA website in October 2000 by Dr Linda Dykes. It was updated in February 2002. This information is brought to you by the Rabbit Welfare Fund - the charitable wing of the Rabbit Welfare Association. If you love rabbits, please consider supporting the Rabbit Welfare Fund. You can make a donation, or you may like to join the RWA. The £17.50 adult subscription includes a subscription to "Rabbiting On", a fabulous quarterly magazine packed with health, behaviour and care advice to help you build a wonderful relationship with your bunny - whether s/he lives indoors or out. Copyright © BHRA/RWA 2000/2002 |
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© Copyright Parkside Veterinary Group |
