Rabbit hemorrhagic Disease (RHD)

Rabbit hemorrhagic Disease

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Changed on: 22.01.2019
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The rabbit hemorrhagic disease (rabbit hemorrhagic disease or RHD) causes important economic losses in the rabbit meat and fur industry and has significant negative ecological impact among wild rabbit populations and indirectly on its dependent predators. RHD has been known since the 1980s. It was first described in 1984 in China. A few years later this epidemic affected also rabbits in Europe. A similar viral disease, also caused by a Calicivirus from the genus Lagovirus, had been detected in hares under the name European brown hare syndrome (EBHS). The causative agent of the rabbit hemorrhagic disease is the RHD virus (RHDV), a  non-enveloped, single-stranded RNA virus from the virus family of Caliciviridae (genus: Lagovirus). The virus is very resistant in the environment outside the host. In 2010, the presence of a new variant of the RHD virus, called RHD virus 2 (RHDV-2), was reported in France.

The rabbit hemorrhagic disease (rabbit hemorrhagic disease or RHD) causes important economic losses in the rabbit meat and fur industry and has significant negative ecological impact among wild rabbit populations and indirectly on its dependent predators. RHD has been known since the 1980s. It was first described in 1984 in China. A few years later this epidemic affected also rabbits in Europe. A similar viral disease, also caused by a Calicivirus from the genus Lagovirus, had been detected in hares under the name European brown hare syndrome (EBHS). The causative agent of the rabbit hemorrhagic disease is the RHD virus (RHDV), a  non-enveloped, single-stranded RNA virus from the virus family of Caliciviridae (genus: Lagovirus). The virus is very resistant in the environment outside the host. In 2010, the presence of a new variant of the RHD virus, called RHD virus 2 (RHDV-2), was reported in France.

Occurrence

The rabbit hemorrhagic disease of rabbits can be detected worldwide, and is nowadays considered as endemic in Australia, New Zealand, America, Asia and Europe. Import/export of rabbit meat was also a factor for the rapid spread of the virus infection. In Australia, the virus was imported from an island that was anchored to the Australian continent. RHVD was purposely introduced here for rabbit biocontrol.

The host spectrum includes domestic and wild rabbits (Oryctolagus cuniculus). The classical RHD virus is very host-specific and not contagious for humans and other mammals. In contrast to the "classical" RHDV, RHDV-2 is also susceptible to field hares. Young animals are affected by RHDV-2 already from an age of approximately 1 month.

In 2014, cases of RHDV-2 were detected for the first time in Germany, 2016 in Austria. RHDV infections in domestic and wild rabbits were occasionally reported in Austria. Up to now, two cases of RHDV-2 (Styria, Salzburg) have been diagnosed by the AGES. The last known outbreak of classical RHD in wild rabbits was at the end of 2016, in Vienna at the Danube Island.

Transmission

The virus is transferred directly from rabbit to rabbit (via secretions and excrements) and indirectly via contaminated inanimated and animated vectors (e.g. contaminated water, food, clothing, shoes, objects, hands, blood-sucking insects). The pathogen transmission can occur orally, nasally, conjunctivally and parenterally via blood-sucking insects.

Symptoms

The incubation period is 1-3 days. Animals usually die after 12-72 hours. Young animals up to 2 months of age do not develop clinical symptoms (juvenile resistance).

The disease is often characterized by a peracute progression which is accompanied by an acute necrotizing hepatitis (liver inflammation) and a generalized coagulopathy.

The peracute / acute progression is characterized by sudden deaths without clinical symptoms or acute drowsiness, loss of appetite, high fever (> 40 °C), bloody nasal discharge as well as occasional respiratory and neurological symptoms (e.g. opisthotonus, paralysis, ataxia).
The subacute / chronic disease progression, however, is rare and is characterized by a milder clinical symptomatic: Icterus, loss of appetite, lethargy. Convalescence after the disease is rather atypical.

Control/prevention

Control/prevention

The control and prevention of RHD is achieved via vaccination prophylaxis and prevention of the introduction of the disease into rabbit population. It is reported that vaccination with a monovalent RHDV vaccine (after basic immunization) followed by semi-annual booster vaccinations, provide additional protection against severe clinical manifestations of RHDV-2 infection. Since autumn 2016, an RHDV-2 vaccine has been approved for fattening rabbits.

Diagnostics

Pathological key features for an infection are a dry tinder-colored liver, congestion of parenchymatous  organs, minor bleedings, a spleen swelling, and a pulmonary edema.

Histologically, acute hepatitis dominates due to the virus-induced destruction of numerous liver cells and acute congestion of parenchymatous organs with hemorrhages and mictrothrombosis (DIC).

In case of suspicion it is recommended to send the animal body for pathological examination to the institute in Mödling. On the basis of the necropsy and histological findings, the diagnosis of RHD is relatively safe, but a distinction between RHDV and RHDV-2 is not possible by pathological examination. The differentiation between RHDV and RHDV-2 can be carried out by means of a further molecular-biological examination (Inst. für klinische Virologie, Veterinärmedizinische Universität Wien).

At AGES, RHD is examined at the Institute for veterinary Disease Control in Mödling (Pathology Center East Mödling).
Address:
AGES-Institut für veterinärmedizinische Untersuchungen Mödling,
Robert Kochgasse 17,
2340 Mödling
Phone:. +43 50555 38112
E-Mail: vetmed.mödlingno@Spam@agesno.Spam.at


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