What is it?
RHD, or Rabbit Haemorrhagic Disease, is a serious and usually fatal infection of rabbits. It is also known as VHV (Viral Haemorrhagic Disease), and sometimes RCV (Rabbit Calicivirus), and there are two variants - RHD1 (which usually causes sudden death) and RHD2 (a newer variant which has only relatively recently been recognised).
What causes it?
RHD is caused by a type of virus called a calicivirus, that is shed by infected and (although it's rare) any who manage to survive the infection. The virus is immune to freezing, and stays stable at room temperature for over 3 months (and longer if it's cold weather). As a result, it can easily be spread from infected wild rabbits to domestic pets, and even to house rabbits, with the virus particles being carried on people's shoes, clothes and even skin. Rabbits that are lucky enough to recover can usually be expected to shed the virus for 6 weeks or longer.
What cats are at risk?
Any rabbit is potentially at risk if preventative precautions aren't taken.
What are the symptoms?
The most common symptom of RHD1 is sudden death - rabbits that appear healthy may suddenly drop dead from the infection without showing any other signs. Sometimes, a rabbit survives longer, and then they will be depressed and lethargic, have a fever, and bleed from the nose or mouth. Very occasionally, a rabbit will recover, but this is unusual. RHD2 is much more variable - sudden death (sometimes with and sometimes without bleeding) is sometimes seen, but more often the rabbit will be ill for several days, perhaps even a week or more, before succumbing. This, of course, dramatically increases the risk that other rabbits will become infected because as long as they are alive, they'll be spreading the virus.
How is it diagnosed?
The clinical signs are characteristic, but not strictly speaking enough for a certain diagnosis. Unfortunately, in most cases the only way to confirm a diagnosis of RHD is by post-mortem examination, because these rabbits do not usually survive long. In living rabbis, blood samples can be sent away for virus isolation testing.
How can it be treated or managed?
There is no treatment for RHD1 or RHD2 - most rabbits will die; those that survive do so because their immune system is able to meet and defeat the virus. In most cases, we would strongly recommend that infected rabbits are put to sleep on welfare grounds, and to prevent further rabbits becoming infected. If a rabbit has a very mild case, it is possible to attempt supportive treatment with fluid therapy and anti-inflammatory drugs, but the risk of complications is high.
Can it be prevented?
Yes - there are vaccines available for RHD1 and (now) RHD2. It is essential, however, that these vaccines are kept up to date, as immunity does reduce over time. In addition, you can minimise the risk of infection by keeping your rabbits isolated from wild ones (as well as birds and rodents that can carry the virus), for example, in a secure double walled hutch, or as a house-rabbit. However, as there is always a risk of bringing the virus into the house, unless you are able to institute full biosecurity precautions (such as foot dips and changing clothes whenever you visit your rabbits), this alone will not be 100% effective, so we would still recommend vaccination.