Scientists have discovered that the fungus that is killing amphibians worldwide releases a toxic fungal factor that disables the immune response of the host animal, killing it, according to researchers at Vanderbilt University. The findings, published in the journal Science, represents a piece to the puzzle as to why the immune systems of amphibians are unable to fight off Batrachochytrium dendrobatidis, Louise Rollins-Smith, associate professor of Pathology, Microbiology and Immunology told the Vanderbilt University News. Rollins-Smith, who has been studying amphibian immune response to the fungus for more than 10 years, said that amphibians have excellent immune systems that are almost as complex as human immune systems and should be able to recognize and clear the fungus but why they are unable to do so remain a mystery.
Batrachochytrium dendrobatidis is decimating amphibian populations worldwide. Dart frog.
Early studies show that some frogs produce anti-microbial peptides on their skin in an effort to fight off the fungus. The fungus penetrates the layers of skin and the immune cell response should be able to clear it.
The Vanderbilt study shows the macrophage and neutrophil cells are not impaired and can fight off the fungus, but at the stage of the fight when lymphocytes should activate, they fail to do so because the fungus exerts its toxic fungal factors, which the researchers also believe causes neurological changes as well.
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"Fungal infection causes rapid behavioral changes — frogs become lethargic and start to crawl out of the water — suggesting that even though the fungus stays in the skin, the toxic material is having effects elsewhere,” Rollins-Smith said.
The research was funded by the National Science Foundation. The lead authors are J. Scott Fites, a graduate student in the Department of Biological Sciences and Jeremy Ramsey, Ph.D, who graduated from the university's Department of Pathology, Microbiology and Immunology. Others who contributed to the paper include Whitney Holden, Sarah Collier, Danica Sutherland, Laura Reinert, Sophia Gayek, Terence Dermody, M.D., Thomas Aune, Ph.D., and Kyra Oswald-Richter, Ph.D.