Viral Haemorrhagic Disease

Viral Haemorrhagic Disease (VHD) of Rabbits

In 1984 an acute, highly fatal disease broke out among rabbits in one unit in China, and spread rapidly to other rabbitries. Its main characteristic was an acute necrotic hepatitis. It only affected animals older than 2 months often resulting in the death of the mother orphaning any baby rabbits. The disease was first seen in Europe in 1988 and was thought to have been imported from China with frozen rabbit meat used in pet foods. It soon spread over the whole continent and was also seen in Mexico and North Africa at about the same time. It was first diagnosed in the UK in 1992 and initial attempts to contain the disease failed. It was first diagnosed in Guernsey by Isabelle Vets in 1993.

Its cause established as a Calicivirus. A similar disease had been seen in hares in Europe since 1980 but this could not be transmitted to rabbits. This was known as European Brown Hare Syndrome (EBHS).

VHD is highly contagious and can be spread directly and indirectly by insects such as flies and also birds. Infection occurs by nasal, conjunctival and oral routes. The virus is very stable in the environment. It can survive for 105 days at room temperature. The incubation period is 1-3 days and death usually occurs 12-36 hours after the onset of fever.

As indicated the incubation period is short and death soon follows so few clinical symptoms may be noticed. Careful observation during the course of the disease may reveal signs such as an elevated rectal temperature (>41 C), anorexia, dullness, lethargy, collapse, convulsions, incoordination, paralysis, groans, cries, difficulty breathing, and bloody discharges from the nose. Other diseases in the rabbit can present with similar symptoms. In some rabbits (5-10% of the population) a more chronic form of VHD is seen. In the chronic disease the symptoms include sever jaundice, weight loss and lethargy. These rabbits will often die within 1-2 weeks of liver failure.

On post mortum there are obvious haemorrhages throughout most of the internal organs, the liver being the most severely affected.

There are many tests that can be undertaken but testing for antibodies can be unreliable as there appears to be a strain of VHD that causes no disease but causes antibody production. The most reliable testing method is to send frozen liver samples to Veterinary Laboratories for electronmicroscopy to look for viral particles.

Vaccination is the mainstay of disease protection. CYLAP is a completely killed vaccine (ie. not a live vaccine) and is the only vaccine currently available in the UK. The vaccine is highly effective and breaks in immunity are very uncommon. Vaccination can be carried out from 14 weeks of age and immunity requires boosting annually. Vaccination against Myxomatosis must not be done within 2 weeks of vaccination against VHD.

The incidence of VHD is probably underestimated as the rabbits die relatively quickly (compared with Myxomatosis) and so are not presented to Vets.