Myxomatosis & The Importance of Vaccination

History of Myxomatosis
Myxomatosis was first seen in the rabbit population in Uruguay in 1896. It is caused by the Myxoma Virus and was deliberately introduced to wild rabbits in Australia, as a form of pest control, around 1926. Australia's rabbit population had been pretty much destroyed by the virus by 1953 during which time the virus was also illegally introduced to France. This gave the virus the opportunity to be spread intentionally across Europe and North & South America. At this time governments had not decided whether or not to make the disease readily available to farmers as a form of biological control, however a french farmer took it upon himself to import the virus to control rabbits on his land. The ferocity of the virus was apparent as it spread, rapidly across Europe within a year. It reached the UK in 1953, the same time the Australian rabbit population was nearing extinction.

Once in the UK, farmers deliberately spread the disease by placing infected rabbits into local wild rabbit burrows however many people were disgusted by the suffering they were witnessing at one poin the RSPCA was regularly heading out specifically to find and humanely euthanise myxi rabbits. Despite this the British government refused to place any legislation on the deliberate spread of the virus leaving 95% of the British wild rabbit population dead by 1955. It was in 1954 that the UK government finally made it illegal to place infected rabbits into new colonies, but by then the damage was done.

What is Myxomatosis?
Myxomatosis is a severe viral disease. It is caused by the Myxoma Virus which is a member of the large Poxvirus group. Most rabbits and hares are susceptible to the virus meaning that they carry the receptor to which the virus can attach itself and work its way into the animals cells. The disease is host specific and cannot be transmitted to humans or other species of animal.

Once a rabbit has contracted Myxomatosis, unless they are vaccinated, it is highly unlikey they will recover. There are very few recorded cases of domesticated rabbits recovering from 'full myxi' although the wild rabbit population does have an improved immune response which has developed from generations of exposure.

How Myxomatosis Is Spread
The disease transmits itself through blood sucking insects such as fleas and mosquitoes. They bite, usually around the eyes and ears, of an infected rabbit and then move onto feed from a healthy rabbit thus transmitting the disease. Whilst mosquitoes only have an average life span of 2-3 weeks, they can travel up to 14 miles in that time. With fleas it is different as though they may not travel very far they are able to feed for over a year and can keep the virus active, within their systems, for well over 100 days.


The Lifecycle
Viruses are so small and contain so little genetic information that they cannot independently reproduce. They rely on infecting a host cell and ‘hijacking’ it, using the cell’s own replication machinery to generate copies of itself. This leaves the cell exclusively generating copies of virus particles at the expense of its own functions and eventually the virus will use the cell’s protein assembly process to ‘build’ new viruses. These then break free from the host cell and go on to each infect another cell and so carry on replicating. Although the virus is not technically ‘alive’ it is very proficient at reproducing and so spreading itself.


Symptoms
The classic symptoms of Myxomatosis are generally only seen in unvaccinated rabbits. It is a truly dreadful disease and causes immense, unnecessary suffering during which a rabbit can take as long as 14 days to die. Most forms of treatment are futile and if your rabbit has 'full myxi' it is likely your vet will suggest euthanasia as the only humane option.

The usual symptoms are runny, swollen, eyes which usually secrete a substance similar to that seen in conjunctivitis. If you notice these symptoms on your bunny, especially if they are not vaccinated, then please check immediately for further sypmtoms. You may find the rabbit also has swollen genitals and/or swollen muzzle too. If a Myxomatosis infection is allowed to run it's full course the eye's may worsen until the rabbit is blind whilst lumps appear all over the head & body and a thick discharge will often seep from the nose and eyes. Most rabbits who contract Myxomatosis die from a secondary infection such as Pneumonia because their immune sytems are so damaged.

Classic Symptoms
• Swollen and runny eyes
• Thick discharge from the eyes and nose
• Swollen genitals and face
• Lumps or 'nodules', all over the head and body

Symptoms in a Vaccinated Rabbit
Vaccinated rabbits can still contract the disease if bitten by an insect vector who is carrying the virus and where this used to be a rare occurence it has become much more prevalent over the past few years. However, in vaccinated rabbits, the symptoms are much less severe and the rabbit has a good chance of survival with supportive care. Vaccination can turn a fatal illness, into something that is treatable by bolstering the rabbit's immune system leaving it preprepared with a antibody store. Myxomatosis found in vaccinated rabbits is most often referred to as Nodular Myxi.

Symptoms can vary in vaccinated rabbits but skin nodules are the most commonly seen. These form deep rooted scabs on the skin which often scar once the bunny has recovered and can range from one nodule, to several, most often sited on the face. You may find swelling around the face, particularly the eyes and nose and on occasion the genitals. Some rabbits develop a conjunctivits but again this is far less severe than seen in the 'full myxi' cases. As with unvaccinated rabbits they are also prone to secondary conditions such as respiratory tract infections related to Pasteurella and your rabbit is likely to become withdrawn and lethargic.

Prevention & Treatment
The best prevention against Myxomatosis is to vaccinate your rabbit. We cannot guarantee that your bunny won’t contract Nodular Myxi, however their chances of recovery are greatly improved than had they been left otherwise defenceless.

Prevention
Although it is very hard to totally prevent your rabbits from coming into contact with Myxomatosis, there are a few steps you can take to help keep the disease at bay.

• Vaccinate– this is by far the most effective way of keeping your rabbit safe from Myxomatosis. Even if your rabbit lives indoors they are still at risk from insects.

• Flea Treatment- if you have other pets in the house such as cats and dogs, ensure that their flea treatment is up to date too and that your home is flea treated, should fleas ever be found. This is particularly important if you have a house bunny. You should also treat your rabbit for flea's if you notice any in his coat.

• Insect nets– Place these over the mesh parts of your hutches and runs. This prevents insects getting into your rabbit, thus reducing the risk of them being bitten by an insect carrying the virus. Some owners use finely laced old net curtains as a cheaper alternative.

• Quarantine– Ascertain whether or not any new bunnies coming into the environment are carrying any fleas or lice that could pass on the virus and treat them accordingly. All new rabbits should be quarantined for at least 2 weeks before integrating with your existing rabbits.

• Cleanliness– Ensure that you keep your rabbits home clean and disinfected in order to reduce the risk of attracting blood sucking insects which are often also drawn to feaces.

• Hay & Straw- Try to buy hay and straw from farms in area's not known for having outbreaks of Myxomatosis and check for any insects that may be living in the bags.

• Water- Eliminate standing water from your garden (and preferably from any neighbouring gardens as well!) as stagnating water is a prime breeding site for mosquitoes.

• Wild Relatives- Make sure that rabbits living outdoors cannot make contact with wild rabbits or hares.


Treatment
If a rabbit is not vaccinated against Myxamatosis and develops the full, classic symptoms, then the chance if survival is extremely small, even with intensive nursing, veterinary support and antibiotic treatment. Usually your vet will suggest that an infected rabbit with full myxi be put to sleep to prevent unnecessary suffering.

If you find that your vaccinated rabbit, still manages to contract myxi, the prognosis is better. The severity of the virus is different in each rabbit depending on what sort of immunity they have developed from the vaccination and their general state of health. You may find your bunny develops just one nodule and is otherwise fit and well whilst others can become very ill. However treatment is available and usually quite successful.

• Your vet should prescribe antibiotics to help your rabbit fight any secondary infections that may occur.

• You may also be required to bring outdoor rabbits inside to ensure they are kept warm and dry at all times.

• If your bun has swollen or infected eye's, you may be given eye drops to help clear the infection. You will also be required to ensure you keep the eyes well bathed to prevent them from becoming sore or dischrage adhesing the eyelids together.

• If your bunny is off his or her food you may be required to commence syringe feeding as demonstrated and instructed by your veterinarian.

• Fluids are essential and if you bunny is not drinking voluntarily, your vet may wish to administer subcutaneous fluid (given under the skin) to keep your rabbit hydrated and the intestinal tract well lubricated.

• Any nodules or lesions, should be left alone and will eventually scab and fall off of their own accord, some of these will sadly scar but most fade over time. Some deeper set leisions can be open to infection so keep an eye on them for blood, pus or discharge

• You must be prepared to be on hand for some intensive nursing if necessary as rabbits recovering from Myxomatosis often require a lot of support from their owners.

If you feel unable or unwilling to provide this level of commited care then speak to your vet about having your rabbit admitted for treatment otherwise the kindest course of action may be to let them go peacefully.

When Enough Is Enough
If at any point you feel that your rabbit is not making sufficient progress and is in prolonged pain or suffering, then it is up to every responsible owner to make the decision to decide to have their rabbit humanely euthanised. Whilst this is unusual in cases of Nodular Myxi it may sometimes be an inevitable outcome if the rabbit is suffering with little or no hope of recovery. Usually it is your vet that will be first to broach this subject so it is worth making sure you absolutely trust their professional opinion and that you have talked through all the PTS options to choose the one most suited to you and your rabbit.

Vaccination
Currently no vaccine can guarantee total protection against Myxomatosis however as previously stated, having the vaccination does mean that if you rabbit should contract Myxomatosis it is likely to be the Nodular and less severe form meaning their life can often be saved. Far too many rabbits are needlessly lost every year to this awful disease and this suffering is totally preventable for just a few pounds.

Vaccinations are required every 6 months.
Domestic rabbits do not have any immunity to the Myxoma virus. In Britain most vets use the Nobi-Vac Myxo vaccine which is made from a harmless virus called Shorpe Fibroma which will allow a rabbit to develop cross immunity against some strains of Myxomatosis because the antibodies developed by the immune system in response to the two illnesses are very similar. Immunity develops after 14 days.

Different vaccines are used in Europe and many of these are reported to have more adverse effects than the Nobi-Vac injection.

How Should the Vaccine Be Given?
It is extremely important to ensure that your vet is rabbit savvy and knows how to give the Nobi-Vac vaccine correctly. It is not given in the same way as the VHD vaccine and correct administration is vital to its effectiveness.

Most vaccines are given subcutaneously (under the skin), however 10% of the Myxomatosis vaccine MUST be given intradermally, between skin layers. This part of the injection is imperative because it stimulates an immune response in the rabbit’s skin which is where the virus will initially gain access (through a bite). Please check your vet remembers the intradermal part of the vaccine by reminding them before the injection is given. There is no other vaccine available in the UK so do not be fobbed off by a vet who tells you it is not necessary. This is the manufacturers recommendation and is printed on the instruction leaflet.

There are two methods a vet can use to give the intradermal dose, one is into the base of the ear with the remaining 90% given into the scruff and the other less commonly used on involves the vet giving the 10% intradermally into the scruff and then either changing the needle for the 90% or pushing the needle shaft deeper to subcutaneously to deliver the remaining 90%. The vet may choose to give the 90% first.

If Your Rabbit Has Not Received The Intradermal 10%
Don't panic. First speak to the vet who administered the initial vaccine and double check that they did not give the Intradermal part into the scruff with the same needle as they delivered the remaining 90% with. If they have not then tell them you wish them to repeat the 10% as in accordance with the Nobi-Vac instructions and that you want it repeated free of charge because they are at fault for not ensuring it's correct administration. Make sure that only the 10% is repeated, not the entire vaccination.


Side Effects
The benefits of the vaccine far outweigh any side effects of which reports are few and far between. If any side effects are noted, they should be reported back to the vaccine manufacturer. Most commonly rabbit's are found to be slightly subdued after the vaccine but usually return to normal within a 24 hours. It is always wise to monitor your rabbit after vaccination and check that they aren’t taking too long to return to their normal eating & drinking routine and that they are still passing droppings.

The only other commonly reported side effect is when the vaccine to causes a slight lump or scab where it has been administered. This is not a bad thing as it means the rabbit is responding well to the vaccination but it is not a cause for concern regardless of whether it does or does not appear.


When Is It Not Safe To Vaccinate?
. Vaccinations against Myxi can be given to rabbits as young as 6 weeks of age. It is not advised that you vaccinate a rabbit younger than this except in circumstances where they are extremely at risk.
. Only fully healthy rabbits should be vaccinated. If your bunny is poorly, wait until they have made a good recovery before having the Nobi-Vac administered. This is to avoid overloading their immune system and causing them to become sicker as they struggle to cope with two infections at once, and to make sure that immunity to the vaccine develops fully by allowing the immune system to focus on producing antibodies to the virus.

Pregnant does should not be vaccinated against Myxomatosis and at least a 14 day gap should be left between the Nobi-Vac and the VHD vaccine (either Lapinject or Cylap), they should NEVER be given at the same time for the same reasons stated above. .


[b]References[b]

• http://en.wikipedia.org/wiki/Myxoma_virus
  
• http://www.kindplanet.org/myxo2.html Myxomatosis - by Dr. Micheal Murray
  
• http://www.radil.missouri.edu/info/dora/RABBPAGE/vir.htm#I.#
  
• http://www.burrill.demon.co.uk/meddoc/myxo.html
  
• http://www.rabbitwelfare.co.uk/resources/content/info-sheets/understanding_myxo_feb06.htm Linda Dykes
  
• http://en.wikipedia.org/wiki/Myxomatosis
  
• http://homepage.mac.com/mattocks/morfz/myxo.html

This Document is Copyright © Charlotte Drew, HappyHoppers Forums Uk . June 2008.UK. ALL RIGHTS RESERVED.

The separate Myxomatosis and VHD vaccines have now been replaced by the joint Nobivac myxo-RHD vaccine. The new vaccine is considered superior to the previous Myxomatosis vaccine as it is live so provides better immunity. It also does not require any special form of administration which the old vaccine required and only needs to be given once a year. Additionally there have not been any reports of the limp associated with the previous VHD vaccine so far. If your rabbit has previously had Myxomatosis then it will require two doses of the new vaccine. Side effects appear to be the rabbits being a bit under the weather for a few days and some rabbits may get scabs at the vaccine site. These will fall off and heal fairly quickly. If your rabbit should experience any side effects from vaccination you should report these to your vet who can report them back to the vaccine's makers.

The vaccine costs significantly more than a single dose of one of the old vaccines but you can expect it to cost less that the cost of the combined cost of the old vaccines for one year (2x Myxomatosis 1xVHD). Charges will vary between vets.