Written by Kerry Greener
Last Edited 8th August 2016
Recent stories in the National Press about a new strain of rabbit haemorrhagic disease (RHD), that kills pet rabbits within days, and has no UK vaccine, is sending widespread panic across Great Britain’s domestic rabbit owners.
There has been an increase in cases of RHD in rabbits that have already been vaccinated, and a new variant of RHD is believed to be responsible.
Most breeders have been familiar rabbit haemorrhagic disease, otherwise known as RHD, but this new variety, that is being identified as RHD-2, is a new strain and is resistant to the typical RHD vaccine.
This is proving a severe and worrying problem in rescue centres and veterinary surgeries and with rabbit breeders and rabbit enthusiasts all over the UK.
Rabbit haemorrhagic disease (RHD) is a highly infectious and fatal disease which affects wild and domestic rabbits. RHD only affects European rabbits (Oryctolagus cuniculus). It does not affect other lagomorphs, such as cottontails, or other small mammals, such as chinchillas, guinea pigs, rats and mice.
This calicivirus (calic meaning 'cup' or 'goblet', thus named from the cup-shaped depressions on the surface of the viruses), was first identified by the characteristic haemorrhages found around the internal organs of the rabbit’s body and it the disease was named ‘viral haemorrhagic disease’ (VHD) or rabbit haemorrhagic disease (RHD), with the latter becoming the standard term in recent years. The acronym RHDV (rabbit haemorrhagic disease virus) is used to describe the virus.
RHD is a universally recognised cause of sudden death in rabbits however vaccination has proved to be an effective control so far and the original strain of RHD although reaching endemic proportions in the UK, was brought under relative control from the 1990s.
The disease then spread to Korea by the rabbit fur industry and subsequently spread to other countries in Asia.
By 1986 RHD had reached Italy and by 1988, it was reported in many countries worldwide, probably introduced and spread by rabbit meat trading.
The wild rabbit population managed to avoid the disease until the early 90s where is was reported that hundreds of wild rabbits on the Scandinavian island of Gotland were seen dead in the fields and many more were discovered dead in their burrows. They were on the verge of extinction in only one week.
In the UK the first
outbreaks of RHD were recorded 1994.
Sadly, in 1997, an insane attempt to biologically control the wild rabbit population on Wardang Island in Australia went disastrously wrong, and the infection spread to the mainland, where it killed millions of wild rabbits and domestic rabbits, and has subsequently meant the enforcement of strict laws governing the ownership of pet rabbits in most Australian territories.
Unfortunately, it was only a matter of time before the infection was surreptitiously introduced into New Zealand.
The first confirmed case in the United States occurred in 2000 in a small breeding colony of exhibition rabbits in Iowa. Twenty-five of the 27 rabbits died with no indication of the source of infection.
In 2010, an uncharacteristic outbreak of RHD occurred in a rabbitry in France in which 25% of rabbits which were vaccinated against normal RHDV died. An emergency vaccination was administered to the remaining rabbits which stopped the mortalities, but it was slower than the usual 7 to 9 days and took much longer to control, taking up to 15 days in most cases.
The wild rabbit population was also affected the same way. Samples were genetically analysed and found the virus causing the fatalities was related to, but highly distinct from, the strains of RHD isolated from previous outbreaks.
This new strain of infection has the potential to devastate a wild rabbit population and can also infect previously vaccinated pet rabbits and unlike RHDV, it also appears to affect hares. This variant was renamed RHD-2, and the virus itself as RHDV-2.
The Invasive Animals CRC national rabbit biocontrol monitoring program has confirmed through laboratory testing that Rabbit Haemorrhagic Disease Virus 2 (RHDV2) was present in three recently deceased European brown hares in Australia – one in Victoria and two in South Australia.
RHDV2 is specific to Lagomorph species, which include rabbits and hares. Australia only has two Lagomorph species – the European rabbit and the European brown hare. In Australia, RHDV2 has now been confirmed in these two invasive Lagomorph species, and has not been found to infect or kill any native or other introduced species. In Europe, RHDV2 has infected European rabbits, Cape hares and Italian hares, and similarly has not infected or killed any other native or introduced species.
By 2011, this RHD-2 was identified in Italy and then it was detected in the UK in 2013, although retrospective sample examinations from previous years suggests it has been present since 2010.
The RHD calicivirus has a preference for liver cells and replicates in the liquid found inside these cells. It is essentially a flesh-eating liver disease, which causes the death of most or all of the cells and tissue of the spleen.
RHD is usually diagnosed at post-mortem (an examination, or autopsy of a corpse in order to determine cause of death). It is suspected as the cause of any sudden death, especially if more than one rabbit in the household has died in the same way.
Death is due to disseminated intravascular coagulopathy or liver failure. Disseminated intravascular coagulation, (otherwise known as DIC which is a pathological process characterized by the widespread activation of the ‘clotting cascade’ - a complex set of negative feedback mechanisms used by the human body as a means of maintaining blood haemostasis - a process which causes bleeding to stop), that results in the formation of blood clots in the small blood vessels throughout the body in small blood vessels in most organs, notably the lungs, heart and kidneys, resulting in fatal haemorrhages.
Three manifestations of the RHD infection may be seen:
RHD has a short incubation period of one to four days. The virus replicates in many tissues, including the lung, liver and spleen, with consequential viremia, (where the virus enters the bloodstream and then has access to the rest of the body) and then subsequent haemorrhage.
RHDV is difficult to kill and can survive harsh environmental conditions. It can survive temperatures of 50°C for up to an hour and is not inactivated by freezing. The virus can also survive in the environment and inside rabbit carcases for months. Carcases from wild rabbits that died from RHD can be a source of infection, by spreading the virus via the faeces of scavengers.
Infection is easily transmitted between infected rabbits by the oral, nasal or conjunctival routes, with the digestive system and respiratory tract as the main portals. Food bowls and bedding can also transmit infection. Only a few virions are required to produce infection.
It is believed rabbits that recover from RHD are potentially infectious to other rabbits for one month. It is not known how long the period is for RHDV-2.
After the initial outbreak in China in 1984, later testing in rabbits exposed to RHDV showed antibodies to the virus in serum collected before the breakout in 1984.
It was therefore suggested that non-pathogenic strains of RHDV could have protected rabbits by stimulating antibody production, and in 1996, a non-pathogenic calicivirus was recovered from breeding rabbits in Italy that protected them against RHD. Subsequent investigations in Australia and the UK revealed the presence of non-pathogenic strains of calicivirus that may confer some immunity to RHD.
Most rabbits younger than four weeks remain unaffected by RHD and develop a lifelong immunity, if exposed to the disease. Unexposed rabbits become increasingly susceptible until 6 to 10 weeks old, when physiological resistance to the virus disappears. This resistance appears to be due to a rapid and effective inflammatory response by the liver, with a continued boost in white blood cells around the sites of infection.
However, this age immunity does not occur with RHDV-2 and both young and nursing kits are prone to infection. In fact, it can affect rabbits of any age but it has also been reported the variant gives rise to lower mortalities than classic RHD, although these reports are not conclusive.
What we do know is there appears to be a longer and more variable incubation period (three to nine days) and a more prolonged period of illness prior to death (up to five days).
Since the discovery of RHD, variants of the virus have emerged and have been named RHDVa and RHDVb. Non-pathogenic strains of the calicivirus have also been found. (Ones that don’t develop into disease).
The RHDVb variant has been recently shown to differ from RHDV in many characteristics, so the virus was renamed RHDV-2. There is an opinion this is a new virus, which is a different serotype (or serovar, meaning there is a distinct variation within this species of bacteria) from RHD.
The term ‘lagovirus’ encompasses all types of RHDV and its variants.
The RHD-2 virus variant appears to be replacing the classic RHDV in continental Europe and now Britain. Although believed to be less contagious than RHDV, RHD-2 is more difficult to diagnose in the early stages, meaning rabbits can carry the disease for a longer.
Subacute or chronic infections were more frequent and more rabbits survived, showing a more protracted disease with weight loss and jaundice.
RHD-2 is believed to have spread through domestic and wild rabbits in continental Europe, where rabbit farming is significantly more prevalent than in Britain, however since March 2016, RHD-2 has been recorded across Cheshire, Devon, Leicestershire, Shropshire, Worcestershire, Leeds and Moray.
It is believed that Devon and Cornwall have the most reported deaths.How is this New Rabbit Disease Spread?
RHD-2 spreads the same way as RHD, through people who have come in to contact with infected animals, through biting insects, flies, other animals, bedding and foodstuffs.
Higher temperatures are also said to help spread the disease.
Neill Gardner, chairman of the BRC (British Rabbit Council) said,
“The biggest worry about this virus is that it is endemic and spreads slower than it kills so it creeps around the country in a more sinister pattern than the first strain.”
Neill added that lack of knowledge of RHD-2 was also a major problem,
“The vast majority of owners don’t know about it.”
He added that the disease was spreading in the warmer weather and,
“Unfortunately, a lot of vets are still saying they have never seen it or that they don’t see it as necessary to vaccinate as they often underestimate the worth of the rabbit.”
In a recent interview with the BBC, Neill worryingly said,
“The fear factor is we don't know how it's spreading, with the former strain there was usually a visible sign, like bloody discharge from the nostrils, now they just drop dead”.
Vaccines are easily accessible for the original virus RHD, however, Hazel Elliott, a member of the British Rabbit Council's governing body, said European vaccine firms were applying for licences in the UK, but was unclear as to when they get them. She also said she was aware of three British breeders who had lost more than 100 rabbits in the past six months.
Peter Smith and his daughter Claudia, 15, from Morpeth, Northumberland, lost 10 of their rabbits within three days in September 2015.
Mr Smith said,
“There were no outward signs whatsoever,” he said.
“I was in the kitchen, which isn’t too far from where our rabbits are kept, and I heard an almighty squeal. We rushed out and one of the rabbits was dead.”
Mr Smith, who keeps up to 50 rabbits at a time and takes them to shows, also said there was no pattern to the deaths, with both babies and adults affected alike.
Sources reveal that at least one pharmaceutical company has produced a new RHDV-2 vaccine but Richard Saunders, a Rabbit Welfare Association and Fund veterinary expert and advisor, said about 1.3 million unprotected rabbits were still at risk in the UK, with the only vaccines that work having to be imported from France and Spain, however he also revealed that the vaccine is expected to soon be licensed in the UK.
For more information about rabbit diseases, see Harcourt-Brown and the World Organisation for Animal Health.
Richard Saunders, as introduced above, now reports that the RWAF has been assessing the disease risk of RHD-2 and the subsequent need to import a vaccine effective against the new variant disease.
He is pleased to account that the RWAF has now successfully established a special import certificate for a suitable EU member state vaccine and placed an order for a small number of vaccines to establish an ordering system into the UK.
A joint vaccine against RHD1 and RHD2 was available from the middle of June 2016 and can be ordered via your veterinary practice.
Filavie, a vaccine manufacturer in France, will be supplying NVS (National Veterinary Services Ltd), a veterinary wholesalers in the UK with the Filavac vaccine.
The licensed vaccination protocol for Filavac RHD / RHD-2 is two injections three weeks apart, with annual revaccination advised.
The effect of one injection only has not been investigated.
As with any vaccine not licensed for simultaneous administration, an interval of two weeks between this and other vaccines is advised.
This new vaccine protects against RHD and RHD-2, but not against myxomatosis; therefore, it does not replace the use of Nobivac RHD-Myxo.
It is also possible exposure to lagoviruses from the wild rabbit population is advantageous for a healthy, vaccinated pet rabbit; it may develop a stronger immunity if challenged. Not all lagoviruses are pathogenic, so natural exposure could be protective.
Standard advice with immunological products not licensed for simultaneous administration is to space them out by at least 2 weeks.
The manufacturer of Filavac advised to administer a single dose of the vaccine, followed by annual boosters in low risk situations, and 6 monthly in the case of breeding does at high risk.
In the UK, it is suggested that 'high risk' situations include rescue centres, any geographical location where
cases have been reported recently, and breeders, unless they
have a strict quarantine policy.
Generalised supportive care is being advised for rabbits that survive RHD2, including fluid therapy, syringe feeding and warmth, but bear in mind these rabbits can be infectious to others so barrier nursing is vital.
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