La Trobe University is leading a quarter of a million dollar research project to develop a vaccine against liver fluke as the troubling parasite that causes the disease develops resistance to existing drugs.
Liver fluke is endemic, mainly in sheep and cattle pastures in southeastern Australia. It also affects pigs, goats, alpacas and deer, as well as humans who live in fluke-infested areas.
The disease is also of considerable concern in Southeast Asia including Indonesia, China, India, the Middle East, Africa and Europe.
Professor of Animal Sciences Terry Spithill says losses in Australia due to liver fluke, in terms of reduced production, stock deaths as well as treatment costs and prevention, are estimated at about $60-90million per year. Globally the figure is about $3 billion.
His recent Australian Research Council supported study – aligned with one of La Trobe University’s new Research Focus Areas (RFAs) Securing Food, Water and the Environment – is being carried out in collaboration with the specialist animal health company Virbac (Australia) Pty Ltd.
Professor Spithill is also co-Director of AgriBio, Victoria’s new $288 million Centre for AgrioBioscience, which opened in April on the University’s Melbourne campus at Bundoora.
A parasitic worm, liver fluke is developing resistance to the drug triclabendazole, also known as Fasinex, currently used to fight the disease.
‘This represents a substantial threat to our ability to control the parasite, with a consequent impact on economic productivity in rural communities in Australia and world-wide.’
Coupled with pasture improvement research also being carried out at Agribio, Professor Spithill says a successful vaccine could lead to substantially greater productivity for the global meat market – ¬maybe up to 15 to 20 percent – without any increase in livestock numbers and environmentally suspect methane emissions.
Using cutting-edge technologies, he and his research team are targeting a complex of the parasite’s proteins also known as ‘tegument proteins’ to try and develop the new vaccine. The team includes Dr Glenn Anderson and Dr Robert Dempster from Virbac (Australia) Pty Ltd based in Sydney.
Professor Spithill says resistance to current drugs used since the early 1980s was first reported in sheep in Victoria 1995. There is evidence that resistant parasites are now also present in beef and dairy cattle in NSW and Victoria.
A most successful parasite
Liver fluke, he says, is probably one of the most, if not the most successful parasite in terms of the number of animals it can infect. It can live inside sheep for many years, and migrates through the liver causing haemorrhage, anaemia and fibrosis, finally residing in the bile ducts.
‘It generally doesn’t kill, but it debilitates. It has insidious effects because producers – particularly in certain regions in Indonesia and Africa where all animals are affected – are not aware what the production level of a healthy animal would be like.’
Professor Spithill says vaccines offer the best long-term prospect for disease control, just as humans are protected for life with polio and hepatitis vaccines.
‘However, parasites don’t act quite like viruses,’ he adds, ‘so there may be a greater need for booster vaccination than with anti-viral vaccines’.
‘There is a threshold level of parasites below which economic losses from liver fluke are minimal. ‘But once you get above thirty to forty parasites per animal, particularly a hundred to two hundred parasites per animal, the economic losses can be substantial.
‘So a vaccine that can reduce parasite burdens below that magic threshold will be economically viable.’
Fundamentally different approach
When it comes to developing that vaccine, Professor Spithill says there are various methods. ‘The usual strategy – and we have done this in the past – is to study the parasite, the molecules it makes, and then rationally select those that look promising for vaccine development.
‘However, we’ve done some work on a particular breed of sheep in Indonesia which are highly resistant to liver fluke.’ In collaboration with partners in Indonesia, Monash and Sydney universities he and his team studied the parasite-host relationship and identified an immune mechanism in these sheep that kills the liver fluke.
‘So our idea is fundamentally different from trying to “pick winning” proteins. We’re relying on the immune response of the resistant host to lead us to the right molecules,’ he says.
Professor Spithill’s six-member research group, working in collaboration with colleagues at the University of York in the UK in 2011, were the first to define these proteins on the surface of the parasite, which they are now aiming to develop into a vaccine.
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