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US Salamander Hotspot Could Fall to New Disease
A newly described fungal disease is killing salamanders and newts in Europe and could soon land on U.S. shores, according to a major new study.
The disease invades the skin of salamanders and newts, and is related to another fungus that has been wiping out frog and other amphibian populations around the world. Researchers say there is time to slow the spread of the new disease, but only with quick action.
"If it gets here, it's going to be really bad," said Karen Lips, a biologist at the University of Maryland who participated in the new research.
That's because the United States is home to the world hotspot of salamander diversity: More species of salamander live in the southern Appalachian Mountains than anywhere else on the planet, according to the North Carolina-based Highlands Biological Station. Unfortunately, these salamanders are likely very vulnerable to the newly discovered fungus. [Biodiversity Threats: Maps of Species Hotspots (Images)]
A disease arises
The fungal threat first reared its head in 2010 in the Netherlands, where volunteers noticed sudden die-offs in wild fire salamanders (Salamandra salamandra), said An Martel, a professor of pathology at the University of Ghent in Belgium, who led the study. The volunteers sent some of the dead salamanders to Belgium for study, but the specimens were too decomposed to make a diagnosis, Martel told Live Science.
Without knowing the cause of the die-offs, the volunteers decided to start an emergency conservation program, trapping wild salamanders and keeping them in captivity in hopes of saving them from disease.
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"When they captured them, they looked healthy and it didn't seem anything was wrong with them," Martel said. "After a few weeks, they started dying in captivity."
The deaths at least gave Martel and her colleagues something to work with. They tested the tiny corpses for known amphibian diseases. All the tests came back negative.
Finally, the researchers isolated a fungus from the infected animals' skin. They discovered that it was a new species, dubbed Batrachochytrium salamandrivorans. The newfound fungal species is a chytrid fungus closely related to another amphibian fungus, Batrachochytrium dendrobatidis, which has driven approximately 400 species of amphibians to extinction or near extinction in the past few decades.
Martel and her colleagues reported the discovery of the new fungus in 2013 in the journal Proceedings of the National Academy of Sciences. In the new study, published today (Oct. 30) in the journal Science, the researchers go several steps further, describing results of a detective hunt to track down the origin of the disease and the identity of its likely victims.
Tracing the infection
First, Martel and her team exposed 35 amphibian species to spores from the deadly fungus, finding that only salamanders and newts contracted the disease. Of those, the vast majority died within two weeks. [In Photos: Bizarre Frogs, Lizards & Salamanders]
"Frogs and toads, they are not susceptible, because the fungus cannot invade their skin," Martel said.
Next, the researchers tested 5,391 species of wild amphibian from around the world, looking for the DNA fingerprints of the fungus. That's when the University of Maryland's researcher Lips got involved.
"They contacted us to see if we had samples that we could contribute to help understand the global distribution of this thing," Lips said. "We sent them a bunch of samples from North America."
The tests revealed the good news that the disease has not yet spread to North or South America. In fact, researchers found it only in Asia and Northern Europe. In Asia, the fungus is not associated with disease outbreaks, killing relatively few individual salamanders and newts. This suggests that the fungus evolved there and survives in tandem with the amphibian population.
To pin down that origin story, the researchers tested species of salamander and newt to find out which could carry the fungus and survive. The scientists found several surviving Asian species, including the Japanese fire-belly newt (Cynops pyrrhogaster), the Chuxiong fire-bellied newt (Cynops cyanurus) and the Tam Dao salamander (Paramesotriton deloustali).
The researchers combined those results with an evolutionary analysis, which revealed the fungus originated about 60 million years ago. Together, those findings strongly suggest that B. salamandrivoranshas been living in more-or-less peaceful coexistence with its Asian hosts for millennia. When transferred to European salamanders and newts that did not co-evolve for millions of years to survive the infection, however, the fungus swiftly turned deadly.
Halting a pandemic
Finally, the researchers turned to one last piece of the puzzle: How did this fungus travel from Asia to Europe? They tested live amphibians in European pet shops, in shipments at London's Heathrow airport and at an exporter in Hong Kong. Three of the animals, two of which were already in Europe, had B. salamandrivorans.
"A lot of the species that have this really ancient history for infection have been in the pet trade for a long time and in really high numbers," Lips said. For example, the researchers report, more than 2.3 million Chinese fire-belly newts (Cynops orientalis) were imported to the United States between 2001 and 2009. Terrarium owners prize the newts for their striking red bellies.
Halting the spread of the disease likely depends on regulating the Wild West pet trade, Lips said. Currently, there is no way in the United States to regulate the live-animal trade. The Lacey Act, enforced by the U.S. Fish & Wildlife Service, covers illegal trade only among protected or invasive vertebrates, mollusks and crayfish — not pathogens or diseases potentially spread by the live-animal trade. Europe is similarly unprotected, Martel added. [10 Deadly Diseases That Hopped Across Species]
The world was unprepared when B. dendrobatidisstarted decimating amphibian populations, said Vance Vredenburg, a biologist at San Francisco State University who has documented these declines but was not involved in the current study. With B. salamandrivorans, there is a chance.
"It's clear that human trade in live animals can affect the spread of pathogens, and this pathogen in particular, so we can stop it," Vredenburg told Live Science. "We can slow it down, at least, with laws and [by] enforcing laws."
People can slow the spread by never releasing pet amphibians into the wild, no matter how much more humane that seems than euthanizing the animals, Vredenburg said.
Citizens can also turn to politics. Two bills under consideration by the U.S. Congress could help regulate the pet trade. H.R. 5156, currently under consideration by committee, would authorize the Secretary of the Interior "to identify and declare wildlife disease emergencies" and to coordinate responses. Govtrack.us gives this bill an 11 percent chance of becoming law. Meanwhile, the Senate Bill 1153 would similarly improve the regulatory process for the live animal trade. Govtrack.us predicts that S.1153 has a 3 percent chance of becoming law.
If inaction continues, salamanders could suffer the way frogs and toads have from B. dendrobatidis, Vredenburg said. Places that once rang out with croaking calls all night are now silent except for the buzzing of insects, he said. Amphibians, which have lived on this planet for nearly 360 million years and survived four mass extinctions, are now dying off 40,000 times faster than they ever have before in the history of the world, Vredenburg said.
"[The fungus] is driving amphibians to extinction or near-extinction in the most protected habitats on Earth," he said. And the fault lies with humans: "We have changed the biosphere," Vredenburg said. "We have made the world a lot smaller by connecting pathogens and hosts in ways that they weren't connected before."
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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.