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Photo: Will Merydith

Around the world, the decline of hundreds of amphibian species has been linked to the mysterious and deadly chytrid fungus Batrachochytrium dendobatidis. More than 300 species are nearly extinct because of this epidemic, and many more have probably already been lost to the disease.

Until now, researchers thought the the fungus occurred only in amphibians, since no studies demonstrated that the fungus can grow on live non-amphibian hosts. National Geographic explains the perplexing situation:

One of the biggest mysteries is how chytrid can persist in a frogless pond. Researchers saw it happen many times and were perplexed: If all of a pond’s amphibians were wiped out, and a few frogs or salamanders came back and recolonized the pond, they would also die—even though there were no amphibians in the pond to harbor the disease.

New research refutes the assumption that only amphibians can carry the disease, however. Field collections in Louisiana and Colorado found that up to 29 percent of the live crayfish recovered were harboring the fungus. The team also found that crayfish presence was a strong predictor of amphibian infection with the fungus.

Bringing their findings back to the lab, the researchers discovered that crayfish maintain the infection for up to 12 weeks. Over 90 percent of crayfish exposed to the disease in contaminated water became infected, 36 percent of which died as a result. Water that the authors filtered to remove the fungus still caused some crayfish to die or resulted in gill infections in others, implying that the fungus may release chemicals that contribute to pathology even in the absence of infection, though this requires further investigation. Finally, they confirmed that crayfish can indeed pass the infection on to amphibians.

No one knows for sure where the fungus originally came from or why it’s been such a problem in recent decades, but this research suggests one way that it could have been spread. Crayfish are sometimes moved from pond to pond as fish bait and are sold around the world as food and aquarium pets.

Their results may eventually help explain B. dendrobatidis‘ virulence, persistence and patterns of spread. And as scientists learn more about which species carry the disease, their research could lead to new strategies for managing this pandemic. The more we can discover about this disease, the better chance we have of eventually finding a solution before the majority of the worlds’ amphibians succumb to a fungal death.

More from Smithsonian.com:

Are Appalachia Salamanders Carrying a Deadly Fungus? 
Three New Frog Species Face an Uncertain Future