Rabbit haemorrhagic disease (RHD), also known as rabbit calicivirus disease or viral haemorrhagic disease, is a highly contagious disease of European rabbits (Oryctolagus cuniculus). It occurs in both wild and domestic rabbits and causes peracute, acute or subacute diseases.
RHD is caused by caliciviruses, small, non-enveloped, single-stranded RNA viruses. Rabbit haemorrhagic disease virus (RHDV) is closely related to the european brown hare syndrome virus, which causes a similar disease in hares (Lepus spp.). There are several genetically and serologically different variants of RHDV. Until 2010, six different genotypes were known which cross-react serologically. These are called “classic” RHDV or RHDV-1. A new serotype, called RHDV-2 or RHDV-b, was first detected in France in 2010 and has since spread throughout Europe and other parts of the world. The disease caused by RHDV-2 is similar to that of classic RHDV strains but is associated with a slightly lower (but extremely variable) mortality rate. RHDV-2 can also infect some hare species and, unlike RHDV-1, also infects very young rabbits.
From January 2018 to September 2019, only 0.5% of Laboklin samples were RHDV/RHDV-1 positive, but 53.3% were RHDV-2 positive. RHDV/RHDV-1 and RHDV-2 are mainly transmitted orally. Contaminated herbage can play a role here. Insects also act as mechanical vectors.
RHDV infections often progress peracutely; affected animals die suddenly or within a few days. Clinically, general signs are seen such as anorexia and lethargy, but also neurological symptoms such as opisthotonus, excitement, ataxia or paralysis. Conjunctivitis and respiratory symptoms such as dyspnoea and nasal discharge (possibly bloody) are also frequently observed. In some cases, an increased tendency to bleed can be observed. The chronic form of RHD only occurs in a small number of animals which then develop jaundice.
Hepatomegaly and splenomegaly are the most common pathologies. Histologically, acute necrotising hepatitis can be detected in affected animals. Bleeding and blood stasis in various organs are frequently observed.
In addition to the clinical examination and histopathology, RHD is mainly diagnosed by virus detection using real-time PCR. Due to the genetic differences between the RHDV strains, both RHDV/RHDV-1 and RHDV-2-specific methods must be used.
Treatment is not possible. A prophylactic vaccination is recommended. Several vaccines are available. It must be noted that vaccination should take place against both RHDV/RHDV-1 and RHDV-2. Currently, RHDV-2 cases are mostly observed in Germany, but classic RHDV strains still occur.