Pseudopithomyces toxicarius – the causal agent in facial eczema in livestock.
Sporidesmin, when ingested by cattle, damages the liver and bile ducts. The damaged liver cannot get rid of phylloerythrin, a breakdown product of chlorophyll, which builds up in the blood causing sensitivity to sunlight, which in turn causes inflammation of the skin. FE has cost New Zealand’s economy an estimated $332 million annually.
Now, a significant breakthrough in understanding FE in livestock has brought New Zealand closer to reducing the disease’s devastating impacts. Until recently, sporidesmin, the toxin responsible for FE, was thought to be made by the fungus Pseudopithomyces chartarum (formerly Pithomyces chartarum).
Earlier this year, a consortium of researchers from AgResearch, Manaaki Whenua, Beef + Lamb New Zealand (B+LNZ) and the Livestock Improvement Corporation were able to show that in fact few Pse. chartarum strains appear capable of making sporidesmin, and a new species, Pseudopithomyces toxicarius, is the primary sporidesmin producer. Pse. toxicarius resembles Pse. chartarum closely and is easily misidentified.
The research reclassified the fungus using global data, which was made possible through the International Collection of Micro-organisms from Plants (ICMP) fungal collection, including a critical 1958 specimen. Providing a clearer understanding of the disease’s causes will also enable better tracing of where it has spread, as well as paving the way for more effective control strategies.
Senior scientist Dr Bevan Weir, an expert on fungi, was a lead researcher in the identification process. “This breakthrough is the result of years of hard work and dedication from our research teams and the farming community,” says Bevan. “Identifying Pseudopithomyces toxicarius as the primary cause of facial eczema is a critical step forward and a testament to the commitment of everyone involved.”
FE risk is currently assessed on-farm using spore counting methods, but because of the above problems of misidentification, the counts may have included non-toxic spores, leading to inaccurate risk assessments. However, the researchers urge farmers to still keep monitoring and participating in studies like the B+LNZ Sheep Poo study, because spore counting remains an important tool for farmers to understand and manage FE risk in their regions.
With a clearer understanding of the fungus that produces sporidesmin, researchers are now better equipped to develop tools and diagnostics that will help eliminate the effects of FE on New Zealand’s farming industry. The work also showcases the long-term value of New Zealand’s scientific collections in guiding future management and control.
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