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Amphibians—the big-eyed, swimming-crawling-jumping-climbing group of water and land animals that includes frogs, toads, salamanders and worm-like caecilians—are the world’s most endangered vertebrates.

Amphibians—the big-eyed, swimming-crawling-jumping-climbing group of water and land animals that includes frogs, toads, salamanders, and worm-like caecilians—are the world’s most endangered vertebrates. One-third of the planet’s amphibian species are threatened with extinction. 

Now, U.S. populations of these vulnerable creatures could face a new foe: the Batrachochytrium salamandrivorans fungus, or Bsal. The Bsal fungus causes an amphibian disease that decimated wild European salamander populations. For more than seven years, amphibian and wildlife disease experts from the USGS have been working on a coordinated response to this disease, including disease surveillance efforts and planning what to do if it is detected in the U.S.  

The rough-skinned newt is a western U.S. species of salamander that is highly susceptible to Bsal, based on laboratory studies. (Credit: Teal Waterstrat, U.S. Fish and Wildlife Service)

As of May 2022, the Bsal fungus has not yet appeared in U.S. salamander populations. However, scientists caution that without preventive measures, the fungus is likely to emerge via the international pet trade or through other human activities. From 2010 to 2014, for example, over 750,000 salamanders were legally imported into the U.S.  

“The eastern U.S. has the highest diversity of salamanders in the world, and the introduction of this new pathogen would likely be devastating,” said Katherine Richgels, a scientist at the USGS National Wildlife Health Center, or NWHC.

Salamanders control pests by eating insects like mosquitos and are food for larger animals. Their moist, permeable skin makes them vulnerable to drought and toxic substances, so they are exceptional indicators of ecosystem health. The health of important ecosystems, including the forests and wetlands where most amphibians are found, are valuable beyond their intrinsic worth. These amphibian havens contribute billions of dollars to the economy by supporting recreation and the fishing and timber industries.

“If we lose salamanders, we lose an important part of what keeps many of our forests and aquatic ecosystems vital, along with the benefits those ecosystems provide for the American people,” said Susan Jewell, a U.S. Fish and Wildlife Service biologist.

 

The salamander situation

This map shows the total relative risk of Bsal by U.S. county. (Credit: USGS, Katie Richgels et. al.)

The Bsal fungus was identified in 2013 as the cause of mass wild salamander die-offs in the Netherlands and Belgium. Bsal likely originated in Asia and spread to wild European populations through the global import and export of salamanders.

In the U.S., the risk of Bsal is highest for the Pacific coast, the southern Appalachian Mountains, and the mid-Atlantic regions, according to USGS research.  

“Because Bsal could be so devastating to native U.S. salamanders if it’s introduced here, we must make sure it doesn’t establish, or become endemic – and that duty is urgent,” said Dan Grear, a wildlife disease ecologist at the USGS NWHC.

In the wildlife health field, a disease is considered established or endemic in a population when that infection becomes constantly maintained in a geographic area. Once endemic, a disease is almost impossible to eradicate.

“Because of the devastating effect that we expect Bsal will have on native U.S. salamanders if introduced, there is an urgent need to ensure it does not establish,” Jewell said.

 

A proactive policy

Chinese fire belly newt
The Chinese firebelly newt is one salamander species that NAS found outside its native U.S. range. (Credit: Jeff Lorch, USGS)

In January 2016, the USFWS issued a rule that lists more than 200 species of salamanders from 20 genera as injurious wildlife under 18 U.S.C. 42(a), also known as title 18 of the Lacey Act. The rule prohibits the importation and some shipment of wildlife species that are officially designated as injurious unless a permit is issued.

“The rule minimizes opportunities for Bsal to be introduced, established, and spread in the U.S.,” Jewell said.  

The USFWS used a Bsal risk assessment published by the USGS NWHC and the USGS Nonindigenous Aquatic Species database, or NAS, to help inform its rule.  

“The NAS site showed us that salamanders had been found outside of their native U.S. range,” Jewell said. “That evidence was useful to our finding that Bsal could establish and spread in the country.”  

By understanding the Bsal threat before a potential arrival, wildlife managers have a critical advantage in fighting the disease.

 

Disease detectives, rapid responders, and a proactive plan 

Scientist swabbing newt.
A USGS scientist swabs a central newt in Wisconsin to look for Bsal.

What if Bsal does arrive in the U.S.? 

USGS NWHC scientists act as wildlife disease detectives, investigating the cause of death during die-offs and screening sick or dead animals for infectious diseases. This disease surveillance could help detect the presence of Bsal in North America early in an outbreak.

But scientists from the USGS Amphibian Research and Monitoring Initiative, or ARMI, weren’t content to wait around until the disease showed up to do something about it. So they began a program of Bsal surveillance sampling on public lands, working with the NWHC to test for signs of the disease.

USGS scientists also proactively led a workshop, developed a report, and helped establish the North American Bsal Task Force to coordinate a response to Bsal. The task force developed is a strategic plan to reduce the likelihood that Bsal would be introduced or become established in North America through education and management actions. The Bsal Strategic Plan highlights resources and strategies that local-level natural resource managers and the caretakers of captive salamander populations can use to watch and sample for Bsal, verify the detection of Bsal, and contain and eradicate the disease if its presence is confirmed.

One helpful resource available is a Rapid Response Plan Template. This template outlines the recommended response to a laboratory-verified detection of Bsal and can be adapted to fit the specific needs of the responsible agency or organization.

“Time is of the essence when wildlife diseases emerge,” said Grear, who is also a member of ARMI. “Early detection can help scientists and management agencies respond as quickly as possible and hopefully eradicate Bsal swiftly if it’s found in the U.S.”

Based on the risk assessment, the ARMI and NWHC began conducting an intensive national Bsal survey in 2016 and published their results in 2020. Bsal was not found, according to that report. 

Still, the Bsal threat raises numerous questions that have yet to be answered.  

“Understanding which other species might be carriers, ensuring early detection of Bsal if it arrives here, rapidly responding if a detection is found, and finding new ways to protect amphibians are all crucial efforts where the USGS can continue to play a key role,” Jewell said.

This map shows the sites where Bsal surveillance sampling by the USGS Amphibian Research and Monitoring Initiative has been conducted. (Credit: USGS)
A map of the United States showing the ranges of the two salamander species that had lethal responses to Bsal in laboratory exposure trials. (Credit: USGS)