Research rwj

Does the new RHD also threaten rabbits??Rabbit Haemorrhagic Disease (RHD), also known as Rabbit Viral Hepatitis or Rabbit Haemorrhagic Hepatitis (RHD). China disease, has been occurring regularly in Europe since the 1980s. But since 2010 a new variant is spreading, which can be contagious even for rabbits.

Even more severely than from myxomatosis, rabbit stockings in NRW have suffered for years from RHD.

The disease was named Chinese disease in 1984, when it first appeared in China in Angora rabbits imported from Germany. Just two years later, the disease led to increased deaths in farmed and wild rabbits for the first time in Europe. In Australia, the pathogen was even deliberately introduced into imported wild rabbits in order to control the man-made plague. In 2010 a new variant appeared in France – RHDV-2. While the original virus only infected 7-10 week old rabbits, RHDV-2 also infected younger rabbits and in addition field hares.

The pathogen

RHD is caused by caliciviruses, which are very closely related to the causative agent of European Brown Hare Syndrome (EBHS). Different courses of disease are observed in wild rabbits. In the case of very rapid onset, spontaneous deaths occur without further signs of disease, while in the acute course, languor, respiratory distress, bloody nasal discharge and convulsions may be observed before the animals die after a few hours. Chronic disease progression is rather rare. In total, up to 100 percent of the rabbit population can die during an epidemic of the new variant. Animals that survive the disease form immunity after a few days, which can protect them from new disease in the long term.

Transmission

Also ferrets as popular hunting helpers are possible virus carriers. Photo: S. Lucker

Infected rabbits excrete the virus with all secretions and excrements, thus the most important transmission route is the direct contact between the animals. However, transmission can also occur through objects, clothing, shoes or mosquitoes and fleas. There is evidence that foxes can briefly shed viable virus after eating infected rabbits. Overall, the virus can persist infectiously in the environment during cold, dry weather for several weeks and months. In NRW areas, epidemic-like outbreaks are regularly reported, leading to the disappearance of whole populations. However, the survival of rabbits in island populations shows that undisturbed development is possible if the virus is not introduced.

Measures to be taken in case of an outbreak in the territory

In the case of acutely deceased wild rabbits, usually only bloody nasal discharge can be detected.

A therapy against RHD is not yet known, only domestic rabbits can be protected against RHDV-1 + 2 with vaccinations. However, some precautionary measures can be derived for wild rabbits from the transmission and long shelf life in the environment:

1. In any case it is recommended to bring dead wild rabbits to a Chemical and Veterinary Investigation Office (CVUA) in NRW for clarification of the cause of death (addresses s. u.), positive virus detections provide clarity about the cause, and the results contribute to the documentation of the spread. The cost of the examination is borne by the research center.

2. All dead rabbits should be removed from the territory and disposed of harmlessly to prevent further spreading.

3. Hygiene measures (change of clothing, cleaning/disinfection of shoes) are important in order not to spread the pathogen to previously unaffected areas. 4. Hunting appropriate to the population (until hunting is suspended) as well as sensibly adapted predator hunting can help to strengthen the remaining rabbit population.

Effect on the wild population

A new variant of RHD is also infectious for hares.

In Spain and Portugal, the IUCN has already classified wild rabbits as endangered. In addition to increasing loss of natural habitats, v. a. RHD and myxomatosis pose the primary threat to this species. Particularly dramatic are also the consequences for endangered predators such as Iberian lynx or Spanish imperial eagle, which depend on wild rabbits as a food source. Also in Germany a decrease of the wild rabbit population is noticeable. In addition, the spread of RHDV-2 is now also relevant for field hares. Recent studies show that the worldwide spread of RHDV-2 would not have occurred without humans as carriers. This clearly highlights the importance of hygiene as a preventive measure against the disease.

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