The first week of March marks the release of the K5 strain of RHDV1, a virus used to control feral rabbit populations. The strain is being introduced in the hope that it will better control the rabbit populations in cooler and wet climates where the current strain has been less successful.
Rabbit Haemorrhagic Disease Virus, commonly referred to as calicivirus, was first introduced in 1996 as a new control measure due to the increasing resistance to myxomatosis, which had been introduced in the 1950s. While it did have quite a dramatic effect on the rabbit population initially, it was found that it was not very successful in wet, cool climates. Further issues were identified in 2009 when it was found that there was a naturally occurring calicivirus, RCV-A1, which confers resistance to RHDV in feral rabbits.
The Korean (K5) strain of RHDV shows promise for rabbit control because it seems to be able to overcome the effects of the protective RCV-A1 calicivirus. However, it is being implemented mostly to help ‘boost’ the effects of the currently circulating strains, and it is not expected to result in the dramatic 90% reduction in rabbit population seen with the original introduction of RHDV1. It is to be considered more in its ability to reduce the growth of the population rather than a culling measure, or as a solution to the problem.
The RHDV2 virus found in Australian wild populations of rabbits in May 2015 is also hoped to help control the rabbit populations. It looks promising; Europe has noted a decrease in rabbit numbers, currently attributed to the virus, and hopefully a similar result will be seen in Australia. It is also hoped RHDV2 will be more effective because it can cause death to young kittens and mature, vaccinated rabbits. However, because the virus has a strong competitive advantage and appears to be replacing circulating strains in Europe, it could cause issues if it is not highly virulent, as it may result in the biocontrol measures being less effective.