The Chinese epidemic (scientific names: Rabbit Haemorrhagic Disease ( RHD for short ), Rabbit Calicivirus Disease ( RCD for short ) and Viral Haemorrhagic Disease ( VHD for short )) is an incurable hemorrhagic virus disease that only affects rabbits according to the current state of veterinary medicine . The cause of the China epidemic are caliciviruses from the genus Lagovirus , which is known as the Rabbit Hemorrhagic Disease Virus ( RHDV ). The most common are the RHDVa and RHDV-2 strains . All rabbit breeds are receptive to both sexes. Young animals up to about a month usually do not become ill, but can multiply the pathogen. Most of the sick animals are older than 3 months. The mortality , depending on the virus strain from 5 to 100 percent, with the currently running observable disease almost exclusively fatal.
In 1984, the previously unknown disease first appeared in Angora rabbits in the People's Republic of China , according to other sources in domestic and farm rabbits that came from Germany . It has since spread worldwide. The symptom complex was observed in Western Europe as early as 1986 ; the virus was probably introduced through farm animals , imported rabbit meat and rabbit wool. It first appeared in Germany in 1988.
Reconstruction of the RHDV capsid
|Rabbit Hemorrhagic Disease Virus|
The pathogen is a calicivirus with an icosahedral shell and a diameter of about 40 nanometers , the so-called Rabbit Hemorrhagic Disease Virus ( RHDV for short ), the type species of the genus Lagovirus ; the second officially recognized species of this genus (as of March 2019) is the European brown hare syndrome virus . At the end of the 1990s, a genetically different type called RHDVa was found in Germany and Italy . In October 2010, another type was detected in north-west France that also caused disease in vaccinated animals. This variant of the disease called RHD2 (nickname English bunny ebola ), triggered by the RHDV variant Rabbit Hemorrhagic Disease Virus 2 ( RHDV2 or RHDV-2 for short ) is endemic in Central Europe (France, Germany), but will also spread from the northwest in 2020 USA and from Canada to the southwest of the USA and Mexico further and further. First, a lower mortality compared to the original strain was described. RHD2 has spread rapidly from France over large parts of Europe. This virus is now considered to be “unpredictable and aggressive” compared to the previous variants. In addition to rabbits, it can also infect brown hares . A new vaccine was developed in Spain and France, but has only been available in Germany since January 3, 2017 and is currently only used in a few veterinary practices. In addition, there are numerous closely related caliciviruses that do not cause disease, but which mostly have cross-immunity with the RHDV. RHD2 is harmless to humans.
The RHDV can be detected in the blood , in the bone marrow , in all organs and in all excretions. Thus, the infection can take place through direct contact and also indirectly through biting insects and flies. Indirect transmission via objects contaminated with the virus (food, clothing, cage inventory) is also possible. The virus remains contagious in the environment for three months at room temperature and seven and a half months at low ambient temperatures.
A major feature of the disease is a profound blood clotting disorder that leads to punctiform bleeding ( petechiae ) in all tissues. Bleeding occurs mainly in the respiratory tract, stomach, intestines and urinary organs. This causes severe breathlessness in the rabbit and blood in the excretions. In addition, there is an inflammation of the liver with tissue destruction as well as fibrosis and calcifications of the liver cells . Another sign of the disease can be apathetic behavior that occurs within a very short time after infection. The China epidemic can be clearly detected by means of a blood test .
The incubation period of RHD is 1 to 3 days. This is followed by an acute to peracute course, which generally leads to death of the animal within 12 to 48 hours. In addition to the petechial bleeding, central nervous symptoms, which are mainly expressed in cramps, are typical of the clinical course. The rabbits utter a high scream in their agony. In the final stage, an overstretching of the head towards the back ( opisthotonus ) is quite typical. The RHD virus causes blood clotting disorders, bleeding in the airways and organ swelling in rabbits.
With the current state of veterinary medicine, RHD is considered incurable. The most effective way of combating the disease is to have an annual vaccination . To what extent the new RHDV strains evade vaccination protection by the established vaccine strains is still open. In addition, epidemic hygiene measures such as quarantine and banning rabbit exhibitions in affected areas have proven to be useful.
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