In 2015, an exotic strain of RHDV, known as RHDV2 was discovered in the Australian landscape. Researchers from across Australia have been monitoring this virus intensively over the past few years and have found that it has suppressed rabbit abundances by an average of 60%, with impacts most pronounced in southern and western Australia.
This result was recently published in the Journal of Applied of Ecology, where the paper states that “serological analyses suggested that RHDV2 arrived in Australia during spring 2014 and spread rapidly through the Australian rabbit population within two years”.
We know that RHDV2 is effective at killing wild rabbits. Our Centre is now working with researchers based at the CSIRO, NSW DPI, PIRSA and VIC DELWP to better understand its interactions with other strains of RHDV. The ultimate goal is to determine whether the virus [RHDV2] could be registered as an additional biological control for strategic use for the landscape management of rabbits.
However, before RHDV2 can be registered through the APVMA, its efficacy needs to be demonstrated. Researchers are now carrying out efficacy testing of RHDV2 in adult and young rabbits, and also assessing the welfare impacts compared to that of other RHDV strains as well as other control options approved for rabbit management
Work is also underway to better understand the extent to which RHDV2 can overcome acquired immunity to RHDV1, and vice versa, and are aiming to understand how immunity passed on from mothers to their offspring influences the timing and outcome of an RHDV2 infection in very young rabbits.
Are we still monitoring disease?
Absolutely, our national rabbit biocontrol monitoring program is still active, and the team will still provide free testing of rabbits that are found dead for all caliciviruses known to circulate in Australia.
Sampling kits include a sampling tube, detailed instructions how to collect a tissue sample and a return envelope, and can be requested via the RabbitScan website and results will be uploaded to the rabbit biocontrol tracker: https://www.feralscan.org.au/rabbitscan/map.aspx?mapMode=rhdv
The team is also investigating if flies can be used as an additional tool to monitor continental scale activity of RHDV. Bushflies and blowflies are a known vector of RHDV, and fly sampling and analysis is carried out in regular intervals at selected sites across Australia to validate this method.
How would rabbit control be improved if we released RHDV2 strategically, rather than letting nature run its course?
Natural outbreaks of RHDV (or RHDV2) occur when a sufficient number of susceptible animals has built up in the population (e.g. through breeding) that can carry an outbreak. Registered biocides and other controls can be applied to populations before this critical mass is reached, thereby preventing numbers from building up, resulting in less rabbit damage.
The monitoring of RHDV provides essential information regarding which virus is active when and where, and if/how this changes over time. This is important information that allows to choose from the available biocontrols/biocides in a way that will maximise management outcomes.
A very important feature of RHDV is that it can fatally infect very young rabbits. In contrast, RHDV1 strains (such as K5) can infect young rabbits but does not kill them, and results in lifelong immunity in the surviving animals. This means that the application of K5 is not recommended during the breeding season as many young animals will survive and may become next year’s immune breeding population. If RHDV2 was available as a registered biocide, it could potentially be a more robust biocide that could be applied year-round, irrespective if rabbits are breeding or not.
You can learn more about the latest rabbit biocontrol science via two important papers:
Cox, T.E., Ramsey, D.S., Sawyers, E., Campbell, S., Matthews, J. and Elsworth, P., 2019. The impact of RHDV-K5 on rabbit populations in Australia: an evaluation of citizen science surveys to monitor rabbit abundance. Scientific reports, 9(1), pp.1-11 – https://www.nature.com/articles/s41598-019-51847-w
Ramsey, D.S., Cox, T., Strive, T., Forsyth, D.M., Stuart, I., Hall, R., Elsworth, P. and Campbell, S., Emerging RHDV2 suppresses the impact of endemic and novel strains of RHDV on wild rabbit populations. Journal of Applied Ecology – https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2664.13548