Rabbit haemorrhagic disease virus

Rabbit haemorrhagic disease virus (RHDV), also known as rabbit calicivirus (RCV), is the type species of the genus Lagovirus belonging to Caliciviridae family. RHDV is an important pathogen that causes a highly contagious disease in wild and domestic rabbits, rabbit haemorrhagic disease (RHD). The virus infects only rabbits, and has been used in some countries to control rabbit populations.

History
Rabbit haemorrhagic disease first appeared in China during the early 1980s. In 1984 the virus that caused the disease was discovered. The virus spread westward and reached Europe in 1988. The virus has since appeared in Mexico, Cuba, Australia, New Zealand and the USA.

Australia
The virus was imported into Australia in 1991 as a potential biological control agent. Testing of the virus was undertaken on an island off South Australia. In 1995 the virus escaped from the island. The virus was subsequently released into rabbit populations throughout Australia in an attempt to control rabbit infestations.

New Zealand
In July 1997, after considering over 800 public submissions, the New Zealand Ministry of Health decided not to allow RHDV to be imported into New Zealand to control rabbit populations. This was backed up in an early August review of the decision by the Director-General of Agriculture. By late August, it was confirmed that RHDV had been deliberately introduced to the Cromwell area of the South Island.

An unsuccessful attempt was made by New Zealand officials to control the spread of the disease. It was, however, being intentionally spread, and several farmers (notably in the Mackenzie Basin area) admitted to processing rabbits that had died from the disease in kitchen blenders for further spreading.

Had the disease been introduced at a better time, there would have been a more effective control of the population. Unfortunately, it was released after breeding had commenced for the season, and rabbits under 2 weeks old at the time of the introduction were immune to the disease. These young rabbits were therefore able to continue to grow and breed back up. Ten years on, now rabbit populations (in the Mackenzie Basin in particular) are beginning again to reach near plague proportions, though have still not quite returned to pre RCD levels.

Viral biochemistry
The RHD virion is 30–40 nm in diameter, shows a characteristic morphology, and is composed of a major protein of 60 kDa (VP60). The 7.5 kb positive-sense ssRNA genome encodes a large precursor polyprotein which undergoes proteolytic cleavage to yield the mature protein. The C-terminal region of the polyprotein gives rise to the p60 polypeptide, which is detected by antibodies against the capsid protein. Furthermore, the presence of an abundant, encapsidated, subgenomic mRNA with coding capacity for VP60 suggests that the major capsid protein could be obtained either by proteolysis of the polyprotein or by translation of the subgenomic mRNA.