Pithomyces chartarum, whcih looks identical to its newly discovered toxic relative. Photo: Landcare Research / supplied
New Zealand scientists studying a complex fungal disease that affects sheep have made a scientific breakthrough.
Facial eczema is a disease caused by a toxin produced by a fungus. The fungus grows in humid conditions and hurts sheep livers, making them very sensitive to ultraviolet light and reducing productivity.
The disease is estimated to cost farmers and the economy $332 million a year.
But new research has revealed there are two species of this fungi in New Zealand pasture, not just one as previously thought.
Scientists have named the new fungus species Pseudopithomyces toxicarius - identified as the primary producer of sporidesmin, the toxin produced by spores of the fungus. The new species is in addition to the better-understood non-toxic Pseudopithomyces chartarum.
The study's lead author Dr Bevan Weir, senior scientist at Manaaki Whenua Landcare Research, said the teams extensively studied the organisms, genomes and toxins found in New Zealand pasture and abroad.
"It was amazing when we got the first DNA sequencing data and there was just this incredibly clear split showing that there was definitely these two species on pasture," Weir said.
"It was a fantastic experience figuring out that we've kind of cracked it, and that in the past there have been reports of non-toxic strains or less toxic ones, and now we know the reason why."
He said the discovery followed years of hard work and dedication by research institutes, the agriculture industry and farmers.
AgResearch, Manaaki Whenua, Beef and Lamb and the Livestock Improvement Corporation were involved in the study, led by Beef and Lamb.
The seven-year project to eliminate the impacts of facial eczema in livestock was valued at $20.75m, and the government assigned $8.3m to it in March last year.
Weir said identifying the primary cause of facial eczema was a "critical step forward" in reducing its impact.
"The complicated thing is that although these species are really genetically distinct and have very different genes, under the microscope they are completely identical. So you can't tell them apart at all, even under our really good research microscopes.
"And this is a problem for assessing facial eczema risk, because at the moment the main method of assessing risk is doing spore counts, and it's still a good method, but some of those spores that the vets and farmers are counting under the microscope will be from the non-toxic species."
Weir said the ongoing sheep poo collection work will help them identify where the toxic and non-toxic species were found around New Zealand - but there were generally very little toxic examples found in the South Island, and more in the North Island.
AgResearch lead author Christine Voisey said the teams were grateful to the farmers that supported the study by providing samples that were vital to this research.
"Working on this project has been one of the most rewarding experiences of my career," she said.
"There is still much to learn about the biology of Pseudopithomyces, but this research brings us closer to developing tools that will help mitigate the impacts of facial eczema on New Zealand's farmers."
Beef and Lamb general manager of farming excellence Dan Brier said the research gave the sector a clearer foundation for developing more accurate diagnostic tools and effective management practices.
Sign up for Ngā Pitopito Kōrero, a daily newsletter curated by our editors and delivered straight to your inbox every weekday.
