When told the subject of her research has a bit of an alien predator vibe, Natacha Hogan is quick to agree.
“Oh, I like that,” said the assistant professor in the Department of Animal and Poultry Science. “When you look at the structures of these mycotoxins, some really are scary looking. Many are very complex structures with multiple rings fused together and many functional groups hanging off the sides. They sort of look like spiders.”
Hogan’s view may be coloured by knowing what mycotoxins do.
These poisonous substances are produced when fungi infect a plant—although their purpose is a subject of debate. Researchers have noted greater volumes are produced when growing conditions are poor, such as when plants suffer from heat stress or insect damage. When plants activate response mechanisms to deal with the stress or damage, they open themselves up to fungal colonization and mycotoxin accumulation. One theory is that mycotoxins actually prevent the host plant from making enzymes that combat the fungi, which allows it to spread.
That’s a little creepy, but things get worse—much worse—when mycotoxins are ingested.
“When these toxins get into animal cells, they can do a lot of nasty things,” said Hogan. “They affect the ability of animal cells to make proteins. So rapidly dividing cells are most dramatically affected—such as immune cells, ones during early embryonic growth and cells that line the gut.”
Along with reduced growth, decreased immune function and reproductive issues, deoxynivalenol or DON (one of several mycotoxins produced by Fusarium fungi) can cause nausea and vomiting—which is why it’s often called "vomitoxin.” It also causes diarrhea, abdominal pain and fever. In humans, it can cause acute gastroenteritis, and also affect growth and immune function. That’s why most countries rigorously test for DON levels in human food, and have strict limits on allowable levels—one part per million in North America, half that in Europe and Asia. There are also maximum levels for livestock feed, but since lesser grades are used for animal feeds, the potential for problems is much greater.
The economic impact in the livestock sector is measured in the billions annually, and that has spawned a global effort to develop fusarium-resistant cereal varieties, come up with effective ways to keep fusarium-damaged grain out of feed and protect animals who ingest it.
Hogan’s passion is learning how mycotoxins wage their terrible war on living organisms.
“I love trying to understand what goes on in an animal when toxicity occurs,” she said before quickly adding, “I know that sounds horrible. But it’s fascinating to look at how normal physiology works and then what happens when you have a compound that disturbs that.”
It was this fascination that persuaded the Prince Edward Island native to abandon her long-held dream of becoming a large animal vet and instead pursue a PhD in toxicology. She initially worked on man-made, industrial toxicants, but mycotoxins and their effect on livestock gave her a chance to marry her two interests.
Her work includes finding acceptable risk thresholds for mycotoxins in feed and reducing contamination by using state- of-the-art seed-sorting technology to physically remove fusarium- infected kernels from feed batches. But another focus is testing feed additives designed to prevent the cells of animals from absorbing mycotoxins like DON.
“The tricky part is that the last thing you want to do is change the nutritional value of feed and alter the uptake of vitamins, minerals, and energy sources,” she said. “So there’s a lot of work being done to figure out what we can add to feed that can remove, detoxify, or prevent the uptake of mycotoxins, but does not bind to nutrients in feed.”
Anything showing potential to reduce their toxicity is being tested. That list includes physical, chemical and biological methods, products derived from clay, diatomaceous earth, microorganisms and even the cell walls of yeast.
“Several manufacturers make these kinds of products,” she said. “For example, protein and lipid constituents on yeast cell walls provide binding sites for DON molecules. This prevents absorption of mycotoxin into cells, across the gut wall and distribution throughout the body. Adding yeast can improve immunity, increasing resistance to infection and regulate the micro-environment of an animal’s digestive tract. So yeast and its components can protect against mycotoxin toxicity from multiple angles. Or at least that’s the idea.”
Unfortunately, there’s another problem.
“When you make feed from grain, you can have a whole complement of mycotoxins,” said Hogan. “So one product may only prevent absorption of one type—which is great, but the best product will have binding and detoxification ability against a wide range of mycotoxins.”
But while the task is huge, so is the resolve.
“This is one of the biggest issues in Western Canada for both grain and livestock producers—we’ve had what you might call some bumper years for fusarium in recent years. It’s certainly a concern for producers, veterinarians, toxicologists and industry.”
The incidence of fusarium spikes in wetter years, but the overall trend since the turn of the century is up. That’s likely a result of the increasing popularity of one of the most positive developments in Prairie agriculture in recent decades—no-till farming. Leaving straw and other plant material on the surface of a field reduces erosion and boosts soil health, but it also provides fungi with a refuge from soil micro-organisms that feed on them.
And scientists know there are lots of fungi producing a vast range of mycotoxins—more than 300 are now known and more are being discovered all the time as detection methods improve.
But Hogan is hopeful the threat of these nasty organisms can be contained.
“What’s really great is that mycotoxin research is often a collaborative effort between academia, industry and government,” she said. “Everyone wants to find the smoking gun, the way to overcome the risk that mycotoxins pose to animal production and human health.”
Glenn Cheater is the owner of High Bluff Media in Winnipeg and Edmonton.