Introduction
A very contagious disease viral haemorrhagic disease (VHD) is one of the main rabbit diseases vaccinated against in the UK, along with Myxomatosis. Viral haemorrhagic disease is also known as the rabbit calicivirus disease (RCD) and this is because the disease is caused by a calicivirus. Animals affected by the disease include both domesticated and wild rabbits descended from Europe. The animals will almost certainly die if infected by the virus between a time period of twelve and thirty-six hours following infection. Once the virus has entered the body, it reproduces and increases its numbers in the liver, thus damaging it. The virus then travels to the organs including the lungs, heart and kidneys and causes haemorrhaging as they trigger blood clots which clog up the major blood vessels. Rabbits in the bracket of the species Oryctolagus cuniculus are the only type affected. For example, American cotton tails do not become infected by the disease.
Viral haemorrhagic disease is transmitted both directly, such as there being contact between an infected and healthy rabbit, and indirectly. Indirect transmission can occur via contaminated surfaces and insects such as fleas. The signs and symptoms of viral haemorrhagic disease include a fever, nasal bleeding, problems with the respiratory system and even collapse. The disease is not currently found to be zoonotic and no humans have been found to have adverse health implications from contact with infected animals. Vaccinations are available in the UK since there is unfortunately no cure against infection from the virus.
Transmission
Transmission can occur in a direct, but also in an indirect manner. Often a healthy rabbit becomes infected following contact with a living or deceased infected rabbit which could either be wild or domesticated. If the rabbit is exposed to the faeces of an animal with the virus then once again the virus is able to be transmitted. Fomites such as rabbit hutches or cages, feeding bowls, hay, straw, woods shavings, water bottles, human clothing, or footwear can often be sources of infection. Additionally, rodents who are near the rabbit can spread the disease. Insect such as fleas are able to act as vectors thus transmitting the virus from rabbit to rabbit. Birds, dogs, and other animals can carry the virus to the rabbit without the knowledge of the owner and so infecting the rabbit.
The virus is able to survive for very long periods of months at a time, around approximately one hundred and five days, in temperatures as high as 60°C or even below freezing. A vital aspect in preventing the spread is good hygiene and there must be as little exposure as possible to the animal from vegetation acquired from areas in contact with other unvaccinated rabbits. Contaminated and inanimate items such as hay and straw should be burned to destroy the virus. Very strong bleaches may also be used, although obviously not on the animal itself.
Symptoms
Initially, a loss of appetite, fever, and lethargy can be observed by the owner in the infected rabbit although it must be noted that rabbits (kittens) younger than six to eight weeks may not even become ill at all and survive. This is because they receive immunity from their mother’s milk. Above this age there may even be signs of slight diarrhoea as a result of contracting viral haemorrhagic disease.
Emotionally difficult for owners, the rabbit may actually scream due to the pain they are experiencing following infection. The animal may even endure muscle spasms. The disease can progress so that the infected rabbit experiences difficulty in breathing and present signs of nasal bleeding. This bleeding will be especially severe in the peracute form of infection and will result in death within a short period of only two days.
In its most severe form, and unfortunately in about one hundred per cent of cases, the unvaccinated rabbit will die as a result of the disease. Some rabbits over the age of eight weeks may be asymptomatic and death can occur suddenly with no warning at all.
Treatment and Prevention
There is no cure to save a rabbit infected by viral haemorrhagic disease. In very mild cases then supportive therapy may be administered to reduce and treat the symptoms and antibiotics are occasionally given to prevent secondary bacterial infections. Unfortunately most unvaccinated rabbits will actually die with or without this treatment. Most infected and unvaccinated animals are euthanized to prevent further suffering.
Vaccinations are highly recommended in the UK and administered as early as eight to twelve weeks old. Annual boosters are then given to provide long term immunity for the rabbit against viral haemorrhagic disease. This form of medicine is preventative and since there is no cure then British vets strongly encourage its use. The vaccination should be given before or after the vaccination against myxomatosis for the minimum time period of two weeks.
Diagnosis and Prognosis
Viral haemorrhagic disease is usually diagnosed after the animal has died due to the rapidity of the fatal effects it produces. Samples are sent to veterinary laboratories where the polymerase chain reaction (PCR) test or ELISA test is used. The virus is isolated and identified. The prognosis for unvaccinated rabbits is extremely poor and results in a very high number of fatalities. Vaccinated animals which have the contracted the disease are more likely to survive.
