Batrachochytrium salamandrivorans (Bsal) is a recently discovered fungal pathogen from Asia that is emerging and causing salamander declines in Europe. Unregulated trade of infected non-native salamanders is believed to be the route of entry.  North America is home to the greatest diversity of salamanders in the world. Currently, no regulations exist in North America that require pathogen-free trade of amphibians. Estimates of trade volume and pathogen prevalence suggest that thousands of Bsal-infected salamanders could have already crossed U.S. borders, although to date, no positive Bsal detections have occurred. Risk models developed by the U.S. Geological Survey based on environmental suitability suggest that the likelihood of Bsal invasion in North America is high. However, these and other risk analyses have not taken into consideration the susceptibility of amphibian host species, which could affect Bsal invasion potential.

In 2016, a collaboration among the University of Tennessee, Tennessee Wildlife Resources Agency, and North Carolina Wildlife Resources Commission began to investigate the relative susceptibility of North American salamander species to the foreign pathogen, Bsal.  One year later the NGOs, Liquid Spark, BAND Foundation, and Amphibian Survival Alliance, joined the effort along with researchers from University of Massachusetts, Vanderbilt University, Washington State University, and Universidad Nacional Autónoma de México. 

“Liquid Spark is proud to that our first 1% for the Planet donation in 2016 started the seed grant for this critical early research on the Bsal threat to salamanders in the Great Smoky Mountains, our agency’s “backyard.” It’s extraordinarily gratifying for us to play a part in a project that ultimately has the protection of amphibian biodiversity on an entire continent – North America – at stake. Fast forward to 2019 – and key grants from federal sources have amplified this project across North America. We support Amphibian Survival Alliance (ASA) because ASA is a proven organization at the forefront of watershed and ecosystem protection. We know our donation goes immediately to work being conducted by Dr. Gray to assess the threat of this invasive pathogen in southern Appalachia. Our relationship with ASA and the UT Center for Wildlife Health has been great; Dr. Matt Gray, the lead scientist on the Southern Appalachians project at the Center for Wildlife Health, Institute of Agriculture, University of Tennessee, Knoxville, TN keeps us apprised of recent research developments and we get to visit his team to see the ongoing experiments and learn how that research translates to field applications. This is a transparent, meaningful conservation partnership at its very best,” said Julie Thorner, president, Liquid Spark, Inc.

This initial collaborative effort resulted in testing 29 North American amphibian species to Bsal infection and development of the disease, Bsal chytridiomycosis. In biosecure environmental chambers, salamanders of these species were exposed at the University of Tennessee to one of four Bsal zoospore doses (103-6), and their condition monitored for at least six weeks. Because Bsal is a skin pathogen, the team swabbed animals every six days after pathogen exposure to estimate Bsal infection intensity. Of the species tested, approximately 75% became infected and 30% developed Bsal chytridiomycosis. Generally, dose-dependent infection prevalence and mortality were observed in susceptible species. Gross signs of Bsal chytridiomycosis included necrotic ulcerations that penetrated through the epidermis and sometimes into granular glands with occasional focal hemorrhaging. In addition, diseased salamanders demonstrated excessive skin shedding and altered behavior. Susceptible species that developed Bsal chytridiomycosis and experienced mortality included five lungless salamander species (Family Plethodontidae) and four newt species (Family Salamandridae). In particular, several species of conservation concern (e.g., Green salamander, Aneides aeneus; Striped newt, Notophthalmus perstriatus) developed Bsal chytridiomycosis. In addition, some abundant species with large geographic distributions (e.g., Eastern newt, N. viridescens; Rough-skinned newt, Taricha granulosa) were very susceptible, and could contribute significantly to the amplification and spread of Bsal in North America. Seven additional salamander species in Plethodontidae, Ambystomatidae, and Cryptobranchidae maintained Bsal infections without disease developing, and could serve as carrier species. The team also documented that some frogs species could become infected with Bsal, illustrating the host range of Bsal is broader that previously thought. Several species that became infected with Bsal are traded internationally (e.g., Mexican axolotl, Ambystoma mexicanum), and could facilitate translocation of Bsal into naïve locations, such as North America. Nine amphibian species tested were resistant to Bsal infections, which is hopeful, and could provide insight into developing disease treatment and management strategies. 

“The invasion of Bsal into North America would be devastating and could result in cataclysmic biodiversity losses that exceed the impacts of Batrachochytrium dendrobatidis and Pseudogymnoascus destructans – two other invasive fungal pathogens known to kill wildlife species,” said Matt Gray with the Center for Wildlife Health, Institute of Agriculture, University of Tennessee.

Our results suggest that most North American amphibian communities will be composed of a combination of amplification, tolerant and resistant host species, which will facilitate the emergence, spread and maintenance of Bsal in the western hemisphere if the pathogen is introduced. Natural resource and wildlife health agencies should deem the introduction of Bsal into the USA, Canada and Mexico as a serious conservation threat, proactively establish regulations to reduce the likelihood of introduction, and support research and planning activities that evaluate disease response and management strategies that could fight an invasion if Bsal emerges in North America.

Bsal represents an existential threat to salamander species in North America.  Salamander are not often seen, yet they perform vital ecosystem services.  The work performed by Dr. Matt Gray is vital to understanding the risk posed by Bsal to salamanders.  Support from Liquid Spark and other organizations is an example of how the private sector, NGOs and wildlife disease experts can come together in the effort to control an invasive wildlife disease,” said Reid Harris, director of international disease mitigation, Amphibian Survival Alliance.

Recent federal grants by the U.S. National Science Foundation (Division of Environmental Biology, Ecology of Infectious Disease Program, Grant #1814520) and U.S. Fish and Wildlife Service (competitive state wildlife grant TN-U2-F19AP00047 awarded to Tennessee Wildlife Resources Agency) are helping expand research on Bsal in North America.  More information of the Bsal project led by the University of Tennessee is available at: https://ag.tennessee.edu/fwf/bsalproject/. 

By Matthew J. Gray, Ph.D., Center for Wildlife Health, Institute of Agriculture, University of Tennessee, Knoxville, TN, mgray11@utk.edu 

Photo: Todd Amacker