Rabbit Biocontrol Advisory Group
RCD and Human Health
The rabbit calicivirus has been reported in 41 countries since being identified in China in 1983. Recent research in Britain indicates that a similar, less virulent virus may have existed in British rabbit populations for several decades.
Since 1983, a large number of people, e.g.: rabbit breeders and fanciers, veterinarians, researchers and hunters, have had extensive and prolonged exposure to rabbits with RCD.
While no humans have been deliberately challenged or infected with the virus (but primates have been), six people at the CSIRO Australian Animal Health Laboratory, who worked intensively with RCD and RCD-infected rabbits over many months, were serologically tested for RCD antibodies. No antibodies were found. This indicates that none of the staff had been infected with the virus, which would have triggered the body’s immune system to produce antibodies.
In 1995 the Office of the Australian Chief Veterinary Officer requested information from chief veterinary officers in all countries where RCD is present, plus the USA. They were specifically asked for any evidence of human infection. Assessing the risks that animal diseases, particularly domestic, pose to humans is a prime responsibility of chief veterinary officers. The sample can be considered a broad one, given the many thousands of people who have been exposed to RCD during widespread outbreaks of the disease.
All those who responded (15 countries) reported that there is no evidence of human infection and that RCD is not considered a public health risk. Provided rabbits are healthy, there is no restriction on sale of rabbits for human consumption from rabbit farms where there has been an RCD outbreak. While some countries reported that during initial outbreaks, questions about risks to humans were raised, after up to a decade of human exposure to RCD, there are still no reports of any effects on humans.
Monitoring for possible risks to humans was taken a step further in Mexico, during its intensive programme to eradicate RCD from their domestic rabbit colonies (note that there are no wild European rabbits in Mexico). Office and laboratory staff of the High Security Laboratory of the Mexico and United States Commission for the Prevention of Foot and Mouth Disease and other Exotic Animal Diseases, consumed RCD-infected rabbits which had been cooked at over 100 degrees C for a minimum of 15 minutes.
Staff were serologically monitored to determine if there was any evidence of RCD infection. During the test period only one person, who actually slept in the same location as infected rabbits, responded serologically. There was a low-level antibody response which disappeared quickly.
This individual’s response is not necessarily evidence of infection, however; it is more likely to be due to the high antigen (i.e.: foreign protein) exposure.
There are anecdotal reports, particularly from the United Kingdom, of humans being infected with the virus. However, these have not been verified medically, despite four technologies being available to test humans for evidence of infection with RCD: immune electron microscopy (IEM); virus capture ELISA; immunohistochemistry/ immunofluroescence with monoclonal antibodies; and polymerase chain reaction (PCR) amplification of defined segments of the genome of the virus.
Additional investigation of the implications of RCD for human health, in Australia, has been initiated there by the Department of Health and Family Affairs, to confirm Australian laboratory results on human exposure. The department is planing to undertake a serological survey of field agency staff and others exposed to RCD following the escape from Wardang Island. It will also seek further comment on RCD and human health from some of the 41 countries where RCD is present. Great Britain has recently advised that RCD will no longer be a notifiable disease. It was designated as such when it first arrived in the UK in 1992, in an effort to reduce spread in domestic rabbitries. Now that the disease is widespread, vaccines are available, and it is not a threat to other livestock or humans, notification is no longer considered to be necessary.
In summary, there is no scientific evidence that RCD infects humans or poses any risk to human health, despite extensive human exposure in many countries. The virus is genetically, antigenically and serologically distinct from other caliciviruses, some of which do infect humans. Field evidence supports all laboratory research, which indicates that RCD is specific to the European rabbit and all the domestic breeds derived from it.
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