Calicivirus Disease, Viral Hemorrhagic Disease

Rabbit Calicivirus Disease (RCD), also known as viral hemorrhagic disease (VHD) of rabbits, is thought to have first appeared in China in 1984 and is now present in much of the world. Rabbits of the genus Oryctolagus are susceptible, which includes most show, pet, and laboratory rabbits. Wild rabbits in the US, such as the cottontail and jack rabbit, are not of the genus Oryctolagus and are not susceptible to RCD. An exception to this is a population of rabbits of the genus Oryctolagus that lives on the San Juan Islands, Washington. Humans and other mammals are not affected by RCD.

Rabbit hemorrhagic disease virus (RHDV) is an RNA virus belonging to the genus Lagovirus of the family Caliciviridae. The disease is a highly contagious virus, and up to 90% of affected animals may die. The disease progresses rapidly, with death occurring approximately 1-3 days after initial infection. The virus is hardy and disease can be transmitted by contact with infected rabbits or their excreta, rabbit products (meat, skins, offal), insects (mechanical transmission), rodents, and contaminated objects, such as cages, feeders, and clothing. Rabbits surviving infection can become carriers of the virus and spread disease to other rabbits.



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In 2010, in both wild and commercially bred rabbits a pathogenic lagovirus RHDV2 which differs from RHDV was identified in France. It is less virulent than the previous described RHDV and RHDVa strains. In addition, the clinical characteristics of the disease are different from those described in "classical" RHD, notably in terms of disease duration, mortality rates and the occurrence of disease chronic forms, which are more frequent.1

Initially the virus replicates within the liver cells and causes necrosis (destruction) of the liver. Further in the course of the infection, the virus spreads to other organs and causes bleeding in the lungs and kidneys. Only rabbits over 6 weeks are affected. This may be due to the presence of the maternal immunity at this time. Rabbits between 4 and 6 weeks may show some clinical signs, but will survive. There are three different clinical forms of the disease.

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  1. Peracute (very sudden and violent) Affected rabbits may die 1-2 days after infection with or without clinical signs. In this from of the disease, a severe bleeding from the nose may be present.
  2. Acute 2-3 days after infection, rabbits lose their appetite, are lethargic, have severe nosebleeds and may scream with pain.
  3. Mild Rabbits have poor appetite and seem lethargic. The infection may clear without treatment within a few days. Affected rabbits may develop diarrhea or "snuffles".

Diagnosis and Treatment

Diagnosis is only possible by virus isolation (making cultures). PCR and ELISA laboratory tests are available. Treatment is not possible for the peracute and acute forms of the disease. Mild cases need supportive treatment and treatment of any secondary infection. Inactivated (killed) VHD vaccine is available. If vaccinating rabbits less than 10 weeks old, it is necessary to repeat after that age. The vaccine provides good immunity against the disease but has a high incidence of vaccine reactions. This is a reportable disease, which means that any veterinarian who identifies it must notify the appropriate governmental authorities.

Nowadays, the disease outbreaks still occur on almost all continents and cause significant mortality rates, being endemic in most parts of Europe, Asia, and parts of Africa, Australia and New Zealand. As a general trend, it seems that in areas where the European rabbit is historically present as wild populations, RHDV is also present and endemic. In contrast, in regions where the European rabbit is mainly present as a domestic or industrial animal, the occurrence of virus (epidemics or rare outbreaks) seems to be correlated with rabbit colony number and density.

References

  1. Emergence of a new lagovirus related to Rabbit Haemorrhagic Disease Virus



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