[This article by Hannah Thomasy originally ran at Ensia and has been republished here with permission.]
Probiotics — microorganisms administered to provide health benefits to the host — seem like the new wonder drug, with some evidence suggesting that they may be an effective treatment for human ailments from gastrointestinal disorders to depression. But disease ecologists don’t think we should stop with humans. They want to see if we can use probiotics to treat diseases in other animals as well.
Except in cases where diseases spread to humans, wildlife epidemics can go largely unnoticed. And yet these epidemics are happening all around us. The deadly chytrid fungus has caused the extinction of 90 amphibian species. White nose syndrome (WNS) has killed more than 6 million bats just in the past 12 years. A bacterium called Vibrio coralliilyticus is bleaching and killing corals from Australia to Hawaii. Now, researchers are using probiotics to help animals fight back.
Combating a deadly fungus
Probiotics come in many different types with many different potential health benefits. Some have been tested to treat or prevent gastrointestinal disorders like irritable bowel syndrome. Chewable probiotics may help prevent oral diseases like dental cavities. Probiotics applied to the skin may improve burn healing. Beneficial microbes can produce compounds that inhibit the growth of disease-causing bacteria, are anti-inflammatory or improve the integrity of the intestinal wall.
Scientists suspect that some bacteria might be useful in treating wildlife diseases as well. “Lots of bacteria that are out in nature produce different types of chemical metabolites that they can use as chemical warfare against other microbes,” says disease ecologist Valerie McKenzie. “That’s a natural process that’s been happening for as long as microbes have been around.”
McKenzie’s lab at the University of Colorado Boulder studies the amphibian skin microbiome — the many microorganisms, from bacteria to archaea to fungi, that exist (and co-exist if all is going well) in and on animals — with the goal of combating the spread of the deadly chytrid fungus. In 2016, her lab showed that probiotic treatment increased survival in captive toads exposed to chytrid fungus. But taking a treatment from the lab into the field is no simple task.
The efficacy of a given probiotic treatment is likely to be affected by an amphibian’s immune system, its current microbiome and environmental factors like temperature, all of which can vary widely in nature. Even once all of these factors have been taken into account, there’s still the question of when, where and how to apply the probiotic.
Field trials seeking to answer these questions are underway. And though the concept of a one-size-fits-all probiotic seems attractive, McKenzie stresses the importance of using native microbes in these trials, because nonnative microbial species could harm ecosystems.
Combating white nose
After at least 100 years of infecting bats in Europe and Asia, the WNS fungus appeared in a cave in upstate New York in 2006. To this day, no one is quite sure how the fungus ended up there or how to stop its deadly march across North America.