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Virus combo gets jump on feral rabbits

The combined release of two common biological control agents in Australia has given farmers and landowners an advantage in the fight against pest rabbit populations.

A joint research project between Flinders University, the Department of Primary Industries and Regions SA (PIRSA), the University of Adelaide, the University of Canberra and the Centre for Invasive Species Solutions has discovered growing immunity of rabbits to the myxoma virus and the rabbit haemorrhagic disease virus (RHDV) due to a positive interaction between the viruses.

Since the release and establishment of rabbits in Australia in the mid-19th Century, farmers and the environment have had to put up with the ecological and financial disasters caused by pest rabbits.

The estimated economic benefit to agriculture from the introduced biocontrols to reduce pest rabbits – myxoma virus in 1950 and rabbit haemorrhagic disease virus (RHDV) in 1995 – exceeds $70 billion.

After analysing 20 years of data collected by PIRSA Biosecurity SA at Turretfield north of Adelaide, the researchers found that the combination of the well-known myxoma virus followed by RHDV provides a greater reduction in rabbits immune to the myxoma virus.

PIRSA Biosecurity SA Research Officer, Dr David Peacock, says it is believed the research is the the first in the world to detect this interaction between the myxoma virus and RHDV.

“We also believe it is the first to record such a positive benefit from one viral biological control agent towards another,” Dr Peacock says.

“It’s a rare demonstration of how an unprecedented, long-term monitoring programme combined with advanced ecological modelling has identified such a novel and important effect.”

Dr Louise Barnett, from Flinders University’s Global Ecology Laboratory at the College of Science and Engineering, says the study found for the first time that this specific combination of two well-known diseases is more effective in reducing pest rabbit abundance.

“This will provide agencies and landowners with more ‘bang for buck’ during their rabbit control programs,” Dr Barnett says.

“Pest rabbits compete with livestock for food and continue to cause enormous environmental and financial damage across Australia, so large-scale efforts to release viruses that limit the population are essential.

“Rabbits continue to pose a challenge for land-management agencies around the world, and our research shows that the cocktail of biological controls reduces rabbit numbers even further than expected.”

Pest rabbits cost the Australian economy up to $250 million each year in lost production and millions more in pest control.

Dr Barnett says the latest study could have major implications for landowners and farmers around the world in reducing the pest rabbit population.

“Potentially, disease outbreaks could be timed more carefully to ensure the death rate rises,” she says.

“Our research indicates that introducing RHDV after rabbits have been exposed to myxoma increases their mortality rate by another 10 percent.”

Flinders University Professor Corey Bradshaw says the data and study tested whether the two viruses are more effective when used in tandem.

“The team tested the theory that exposing rabbits to one disease altered the likelihood the population would die from the second virus, and that’s when we discovered the mortality rate from RHDV was higher than expected when a rabbit had already been exposed to myxoma virus,” says Matthew Flinders Fellow in Global Ecology, Professor Bradshaw.

The discovery has global implications with European rabbits causing environmental and agricultural damage in places such as Australia, the United Kingdom, New Zealand and in parts of South America.

The discovery will also assist efforts to save the rabbit in its natural range in Europe and support Australia’s search for other rabbit biocontrols.

Futher implications for other biological control programs are yet to be explored.

‘Previous exposure to myxoma virus reduces survival of European rabbits during outbreaks of rabbit hemorrhagic disease’ by L Barnett, T Prowse, D Peacock, G Mutze, R Sinclair, J Kovaliski, B Cooke, CJA Bradshaw has been published online at the Journal of Applied Ecology.

Source: Flinders University

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