There is a lot happening regarding caliciviruses and rabbit control in Australia – and it heightens the importance of maintaining research efforts to combat feral rabbits, according to Peter Alexander, Chairman of the Foundation for Rabbit Free Australia.
The rabbit calicivirus (RHDV1 – Rabbit Haemorrhagic Disease Virus) first appeared in China in 1984, and was declared a biological control agent in Australia in 1995 where it had immediate impact, especially in drier areas.
RHDV1 was less effective in cooler, high rainfall areas where some rabbits have antibodies to a benign calicivirus that has long been present in Australia. The benign calicivirus doesn’t kill rabbits it infects, but antibodies resulting from those infections offer rabbits some protection against RHDV1.
In 2010, Australian researchers started looking at strains of RHDV1 from other countries to see if any of them were better at killing genetically resistant Australian rabbits, or rabbits previously infected with benign caliciviruses. RHDV1-K5 is a virus from Korea that proved more lethal against rabbits with immunity to benign forms of RHDV, and is now being released through a government controlled program in Australia.
In 2016 a different form of RHDV, RHDV2, appeared in Australia and began to spread across the country. It is highly lethal to rabbits and is effective against those with immunity to other forms of RHDV.
“The Foundation for Rabbit Free Australia is excited by the prospect of RHDV1-K5 and RHDV2 making sustainable rabbit control more achievable for landholders in both the agricultural and the arid zones,” Mr Alexander said.
“The Foundation has been able to contribute to some of the research behind biological controls for wild rabbits, but there remain significant knowledge gaps.”
With the release of RHDV1-K5 in Australia, especially targeting cooler, higher rainfall districts, and RHDV2 also spreading, researchers will be keen to understand which virus is proving most effective in different regions and how best to manage the spread of effective disease carriers.
Landholders are urged to assist by recording rabbit deaths and providing samples for analysis to aid research into the spread of different variants of the calicivirus. The RabbitScan app, available from the PestSmart website, is a handy tool for tracking where rabbit viruses are active and to help with providing tissue samples.
“Without research we would still be facing rabbit plagues, and without research we could fail to optimise the benefits of all the effort that has gone into one of the most successful biological control campaigns in Australia,” Mr Alexander said.