Viral Haemorrhagic Disease [VHD] & Vaccination

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Viral Haemorrhagic Disease [VHD] & Vaccination

Post by Happy Hoppers on Wed Jun 18, 2008 8:28 pm

Also known as Haemorrhagic Viral Disease [HVD], Rabbit Haemorrhagic Disease [RHD], Rabbit Calicivirus Disease [RCD] and Rabbit Viral Haemorrhagic Disease [RVHD]

A History of VHD

The first recorded VHD outbreak affected domestic Angora rabbits in China in 1984, although at the time it was simply referred to as ‘Malattia-X’. After speading to Korea within months, China quickly developed an inactivated vaccine in an attempt to iradicate the disease but to no avail. It reached Italy in 1986 and, from there managed to spread through most of Europe by 1988, presumably through frozen meat consignments destined for the pet food trade. It had arrived in Britain by April 1992, spreading from the South West until, in 1995, a total of 512 cases were reported from across Scotland, England and Wales. Only 8 of these diagnosed cases were in wild rabbits.

VHD has since appeared in Mexico, Cuba, Australia, New Zealand and the USA, most likely travelling through the meat and fur trades and through shipments of infected rabbits. It is now prevalent in Bolivia and there have been reported cases in domestic rabbits in the Russian Federation, India, the Middle East and North & South America.

Reports suggest that VHD (then dubbed Rabbit Calicivirus Disease or RCD) was imported to Australia in 1991, its intended use being that of a biological control agent. When quarantined testing began on Wardang Island in 1995, despite painstaking precautions, the virus managed to circumvent quarantine, cross several miles of ocean, and escape into the outback where it proceeded to decimate the Australian rabbit population with alarming speed and efficiency. The use of VHD was is akin to that of the deliberate spread of myxomatosis in the 1950s and it has been an effective method of population control for over a decade.

Whilst authorities in New Zealand authorities decided not to use VHD as a control agent some farmers took matters into their own hands and in August 1997, a case was reported in Central Otago on the South Island. Attempts at containing the virus failed because farmers were encouraging the spread of disease by offering carrots laced with the livers of infected rabbits. This led to authorities offering official batches of VHD for sale and to legalise it as a biological control, which they did in September 1997.

VHD is now well established in Australia, New Zealand and Western Europe in both domestic and wild rabbit populations so the risk of pet rabbits contracting the virus is a very real threat.

What is VHD?

Viral Haemorhagic Disease (often referred to as Rabbit Viral Haemorhagic Disease) is widely believed to be a calicivirus that primarily affects the domestic rabbit and is specific to the European rabbit (Oryctolagus cuniculus). It is a lethal disease that kills almost all rabbits that contract it, spreading easily and rapidly through populations.
The virus itself is a single stranded RNA, has a no nucleic acid envelope (see here for more details on viruses) and is extremely hardy: able to survive unprotected for several months and withstand temperatures of up to 60C (140F).

Viruses are not strictly living organisms, nor are they ‘not alive’. VHD contains a small amount of genetic information in the form of RNA (RiboNucleic Acid). The VHD virus is usually around 35nm in diameter (1nm, or nanometre, is equal to one millionth of a millimetre), 1,000 times smaller than the average E. coli bacterial cell - 35µm in diameter (1µm, or micron/micrometre, is equal to one thousandth of a millimetre). Since a viral infection is different to a bacterial infection, VHD will not respond to antibiotics making viral infections notoriously hard to treat. There are antiviral drugs available for human infections some of which act by "changing the genetic material of the host cell so the virus cannot use it to reproduce, and others act by blocking proteins on the viral capsule that the virus needs to infect host cells” . In humans, symptoms are usually treated rather than the virus itself, for example cold and flu medications.

VHD, although part of the Calici family, is assigned to a separate group, the Lagoviruses, as the positioning and content of its genetic material is so similar to the European brown hare syndrome virus that they are now grouped together.

Rabbits under the age of 8 weeks are almost entirely resistant due to the immunity passed on from maternal antibodies, although often the mother will die from VHD, leaving the suckling young helpless. Data shows that around 40% of rabbits aged 5-8 weeks survived experimental infection, but only 10% of rabbits over 9 weeks old survived.

VHD has an incubation period of 1-3 days and most rabbits die of the disease one or two days (laboratory tests have shown on average 42 hours) after infection. All experimentally infected adult rabbits died from the virus, although studies on wild populations have shown that approximately 18% of rabbits infected did survive the disease.

Pathologically speaking, VHD causes the ‘clumping’ of red blood cells resulting in clots which subsequently block blood vessels in major organs. This results in haemorrhaging within organs such as the heart, spleen, respiratory & digestive systems and sometimes even the kidneys.

How is it spread?

The majority of our knowledge of the spread of VHD is from Australia and New Zealand, having studied its epidemiology as part of the research prior to its release as a biological control. Very few viral particles are needed to infect a rabbit and so VHD is suprisingly easy to spread. It can be transmitted by direct contact, oral/faecal contact and even the wind. Fomites are also a major transporter of VHD. A fomite is “any inanimate object or substance capable of carrying infectious organisms (such as germs or parasites) and hence transferring them from one individual to another” , and so VHD can be carried on clothing, shoes, car tyres, toys, cleaning cloths/mops etc. Although humans cannot contract the virus (it is specific to rabbits), we can still pass it from animal to animal and so care must be taken if returning from a known infected area.

Scavengers such as foxes, ferrets and even certain birds can transmit the disease through eating infected meat and passing the virus in their faeces or even carrying the virus on their coats. Fleas, flies (especially those of the genus Phormia) and mosquitoes can also spread VHD.

As previously mentioned, the virus itself can survive for several months without a host and so it is not uncommon for a pet to become infected via a second-hand hutch, bedding, food, feeders and even water. If you are buying a second hand hutch make sure you ask what happened to the previous occupant and always sterilise it before using it to house your own rabbit, even if the previous owner has cleaned it themselves. If one of your rabbits does contract VHD be sure to sanitise or completely remove all items in its cage to avoid speading the virus.

VHD seems to spread much quicker in cool, humid climates and so outbreaks are usually during winter or early spring.

The Lifecycle

Viruses are so small and contain so little genetic information that they cannot independently reproduce. They rely instead on infecting a host cell and ‘hijacking’ it, using the cell’s own replication machinery to generate copies of itself. Unfortunately, the cell is now exclusively generating copies of virus particles at the expense of its own functions and eventually the virus will use the cell’s own processes to assemble new copies of itself. These then release themselves from the host cell (either by budding off from the cell or destroying it completely, a process called ‘lysis’) and go on to each infect other cells and so on and so forth. Although technically not a lifecycle as it is not ‘alive’, this is the way VHD multiplies.

Symptoms

A rabbit usually becomes infected via the nose, mouth or conjunctiva (a protective layer over the surface of the eyeball) and so sometimes symptoms will include bleeding from these areas. Most often, however, there will be no symptoms at all following infection and an apparently healthy rabbit will just “drop dead”, sometimes mid-mouthful. This often leads owners to assume that their pet has had a heart attack due to stress or fright, succumbed to heatstroke, or simply “not been strong enough”, resulting in very little accessible data for studying just how prevalent the disease is in the UK. VHD often goes undiagnosed, especially if the pet has died suddenly and asymptomatically, because post mortem examinations are not carried out.

Symptoms are as follows:
• Squeals, grunts or moans
• Collapse/unconsciousness/coma
• Loss of apetite
• Difficulty breathing
• Fever (>41oC)
• Swollen eyelids
• Bleeding from the eyes
• Limited mobility/paralysis
• Convulsions
• Bloody nasal discharge on death
• Jaundice
• Weight loss
• Lethargy
• Constipation/diarhhoea
• Stomach cramps

**Please note this is not a comprehensive list and just because your rabbit exhibits one or more of the above symptoms does not mean it has VHD. Many of these symptoms are shared with other diseases and most commonly VHD will present no external symptoms. If you are in any doubt get your rabbit to a vet immediately.**


Last edited by Sooz on Mon Jun 30, 2008 8:50 pm; edited 7 times in total
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Re: Viral Haemorrhagic Disease [VHD] & Vaccination

Post by Happy Hoppers on Tue Jun 24, 2008 6:14 pm

Prevention & Treatment

Prevention
Although it is very hard to totally prevent your rabbits from coming into contact with VHD 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 preventing your rabbit from contracting VHD. Even houserabbits are at risk so ensure your vaccinations are current. There is more information on vaccinations below.
Sterilise any second hand items intended for your rabbit especially if the owner doesn’t know why their rabbit passed away - it could well have been undiagnosed VHD.
Don’t handle strange rabbits (e.g. in pet shops, a friend’s rabbit) as they could well be carrying VHD. If you have handled a strange rabbit, ensure your hands are washed and clothes and shoes are changed before coming into contact with your own.
Always wash your hands after handling a rabbit.
Keep cages clean by washing them out regularly with a proper disinfectant.
Keep away from wild rabbits and where they eat. Do not feed your rabbit anything grown in or picked from a known territory of wild rabbits or sourced from a known infected area.
Keep strangers away. If your rabbits are housed outside then do your best to keep foxes, ferrets, birds and other rabbits away from your hutches and runs. Weld mesh is a good way of deterring even the most persistant animals but ensure there are no gaps under your run! Also make sure than any wild rabbits stay away and, if you cannot do this, at least make sure they cannot come into contact with your rabbits (perhaps a small weld mesh to avoid any nose-to-nose contact).
Sweep up spilt food and bedding as this will attract mice and other vermin which could easily spread the virus to your rabbits.
Quarantine any new rabbits for at least 7 days and watch for signs of infection.


Vaccines
VHD has no known cure and almost all rabbits die once they have contracted the disease. There is, however, a vaccination available which is highly effective. The vaccines against VHD are inactivated vaccines. This means that the viral particles within the vaccine have been killed or “inactivated” using heat or chemicals. They still retain the antigens to allow the host’s immune system to recognise the virus and subsequently build up antibodies to protect against it. Inactivated vaccines are usually less effective than active vaccines, which contain live but less virulent versions of the pathogen but are much more likely to make the host ill but the VHD vaccine has proven itself to be very efficient.

The most commonly used vaccination is Cylap which is usually administered at around 10 weeks of age although your vet may prescribe it for rabbits as young as 5 weeks if they are in a high risk situation. If vaccinated at 5 weeks, they will need to be re-vaccinated 4 weeks later to ensure continuous immunity. Immunity from Cylap takes 21 days to develop.

A less well-known vaccination is Lapinject which became available in 2007. This can be administered from 5 weeks of age and only takes up to 6 days for the rabbit to develop immunity.

Both vaccines are oil based and injected subcutaneously (just under the skin). Annual boosters are required for VHD vaccines to ensure continued immunity against the disease. Please also note that there must be a minimum 2 week gap between VHD and Myxomatosis vaccinations, some vets prefer to wait longer.

Side Effects
Common side effects of the VHD vaccine include:
• Loss of apetite
• General malaise and disinterest for a couple of days following the vaccination.
• Swelling or irritation at the site of injection about a week after the vaccination, sometimes resulting in fur loss and scabbing.
• On very rare occasions death can occur due to anaphylaxis (allergic reaction).

There is, however, an unofficial side effect to the VHD vaccine, commonly known as “VHD Limp”.

“VHD Limp”
This is a condition whereby the rabbit develops a noticeable limp usually around 24 hours after the vaccination. It is thought to be caused by the oil in the vaccine affecting the nerve supply to the front legs. The limp is often accompanied by swelling on the leg itself (you may need to palpate the leg to notice this depending on how fluffy your rabbit is!) and the rabbit will be visibly favouring one leg. The limp usually disappears within around 3 days and there seems to be a much lower incidence of VHD limp when Lapinject is used over Cylap. Some owners prefer for the vaccination to be administered off centre, avoiding major nerve pathways and so lowering the chances of VHD limp occurring.

There is very little documentation on VHD limp and it is the subject of much debate between owners and veterinary professionals as many vets (and certainly the manufacturers of the vaccine) seem unwilling or unable to confirm a connection between the vaccination and the limp. Most of the information available is either from word of mouth or internet forums such as this one. Be advised though, it is a very real side effect!

Often VHD limp is diagnosed as a muscular or skeletal problem and sometimes a vet will prescribe anti-inflammatories, antibiotics and/or painkillers and even advise an X-Ray (always performed under general anaesthesia). It is a personal judgement call as to whether you wish to put your rabbit through a GA and take the small risk involved with this procedire. If you think your rabbit could have VHD limp it might be sensible to wait 24 hours and see if the limp improves before considering more drastic treatment.

References

B.D. Cooke (2002) ‘Rabbit haemorrhagic disease: field epidemiology and the management of wild rabbit populations’ Rev. sci. tech. Off. Int. Epiz. 21 (2) p347-358 - (http://www.oie.int/eng/publicat/rt/2102/COOKE.pdf)

John C. Brown (2000) ‘What the heck is a virus?’ – (http://people.ku.edu/~jbrown/virus.html)

Wikipedia entry (2008) ‘Rabbit Haemorrhagic Disease’ – (http://en.wikipedia.org/wiki/Rabbit_haemorrhagic_disease#Symptoms)

Dr Main Cooper ‘Rabbit Viral Haemorrhagic Disease (RVHD)’ – (http://213.121.208.4/publications/on-line/advisorynotes/31/31.htm)

Rabbit Welfare Association, Dr Linda Dykes &Judith Brown BVM&S MRCVS (2007) ‘VHD: what every UK rabbit owner needs to know’ - (http://www.rabbitwelfare.co.uk/resources/content/info-sheets/VHD_UK.htm)

IsabelleVets (2003) ‘Viral Haemorrhagic Disease (VHD) of Rabbits’ – (http://www.isabellevets.co.uk/health_advice/rabbit/info/viralhaemorrhagic.htm)

Ingleburn Veterinary Hospital (2007) ‘Vaccination is our only protection’ – (http://www.ingleburnvet.com.au/vacc_rab.htm)

FluSTAR (2008) ‘Treatment of Infectious Viral and Bacterial Diseases’ – (http://www.flustar.com/infectious_treatment.asp)

This Document is Copyright © Helen Coulson,, HappyHoppers Forums Uk. June 2008.UK. ALL RIGHTS RESERVED.
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Re: Viral Haemorrhagic Disease [VHD] & Vaccination

Post by cheryl'n'bruce'flo on Sun Apr 27, 2014 8:48 pm

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.


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