Rabbit hemorrhagic disease
Rabbit hemorrhagic disease
Rabbit hemorrhagic disease (RHD), or China disease, can cause high economic losses in the rabbit meat and fur industries when epidemic occurs. An outbreak has significant negative ecological impacts on wild rabbit populations and indirectly on their predators. RHD has been known since the 1980s.
The causative agent of rabbit hemorrhagic disease is RHD virus (RHDV), an unsheathed, single-stranded RNA virus of the virus family Caliciviridae (genus: Lagovirus). The virus is highly resistant outside the host. In 2010, the emergence of a new variant of the RHD virus was reported in France, referred to as RHD virus 2 (RHDV-2). Rabbit hemorrhagic disease (RHD) was first described in China in 1984. A few years later, an epidemic occurrence of this disease was also detected in Europe. A similar viral infection, also caused by a calicivirus from the genus Lagovirus, had previously been detected in brown hares under the name European brown hare syndrome (EBHS). The rabbit hemorrhagic disease virus (RHDV) is distributed worldwide. One of the ways it has spread has been through import/export of rabbit meat. The starting point for the spread of the virus in Australia was an island offshore from the Australian continent. There, the virus was used experimentally to decimate the wild rabbit population. The host range includes domestic and wild rabbits(Oryctolagus cuniculus). Classical RHD virus is highly host-specific and is not contagious to humans or other mammals. In contrast to the "classical" RHDV, field hares are also susceptible to RHDV-2. RHDV-2 affects young animals as young as about 1 month of age. Cases of RHDV-2 infection were first detected in Germany in 2014 and in Austria in 2016. RHDV infections in domestic and wild rabbits are repeatedly reported in Austria.
Control and prevention of RHD is via vaccination prophylaxis and prevention of introduction into rabbit herds. It is reported that monovalent RHDV vaccines provide additional protection against severe clinical manifestations of RHDV-2 infection after basic immunization followed by biannual booster vaccinations. A RHDV-2 vaccine has been licensed for rabbits for fattening throughout Europe since fall 2016.
Pathogen transmission occurs directly from rabbit to rabbit (via secretions and excretions) and indirectly via contaminated inanimate and animate vectors (e.g., contaminated water, food, clothing, shoes, objects, hands, blood-sucking insects). Pathogen ingestion can be oral, nasal, conjunctival, and parenteral via bloodsucking insects.
The disease is characterized by a usually peracute course associated with necrotizing hepatitis (liver inflammation) and generalized coagulopathy. Diseased animals usually die after 12-72 hours. The incubation period is 1-3 days. Young animals up to an age of about 2 months do not contract classical RHDV infection (juvenile resistance), whereas they may contract RHDV-2 infection from an age of 1 month. The peracute/acute course is characterized by sudden deaths without clinical signs or after acute onset of dullness, loss of appetite, high fever (> 40 °C), bloody nasal discharge, and occasionally respiratory and neurologic signs (e.g., opisthotonos, paralyses, ataxia). The subacute/chronic course, on the other hand, is rare and characterized by milder clinical symptoms: icterus, loss of appetite, lethargy. Convalescence after the disease is rather atypical.
The main findings at autopsy in deceased rabbits were a dry, friable, scale-colored liver, congestive organs, minor hemorrhages, splenic swelling, and pulmonary edema.
Histologically, acute hepatitis due to virus-induced death of numerous liver cells and acute congestive organs with accompanying hemorrhage due to coagulopathy and microthrombus formation predominated. Based on postmortem and histologic findings, the diagnosis of RHD is relatively certain, but differentiation between RHDV and RHDV-2 is not possible. The distinction is made by molecular biological methods.
In case of suspicion, it is recommended to send the carcass for pathological examination to relevant institutes, e.g. to the Institute of Veterinary Medicine Mödling.
Last updated: 12.06.2023