A new form of chytrid fungus threatens US salamanders

Nearly a third of our planet’s amphibians are in decline, but most of the attention thus far has been focused on frogs. The usual causes for wildlife decline are certainly to blame – habitat loss, pollution, climate change – but frogs also have to contend with an infectious disease called Chytridiomycosis, which is caused by a pathogen called Batrachochytrium dendrobatidis (Bd), also known as the chytrid fungus.

Chytridiomycosis is a nasty disease, first making infected animals anorexic and lethargic. Frogs then grow thicker skin, which impedes their ability to absorb nutrients (and for some species, their ability to breathe) from the water in which they live, while they simultaneously lose skin on their limbs. Their hind limbs often convulse. They grow ulcers, and then they start to hemorrhage. The frogs lose their fear, making them easily susceptible to predation, as well as their righting response, which suggests that they no longer have a good sense of their location and orientation in space.

In 2013, a related fungus was discovered called Batrachochytrium salamandrivorans (Bsal). As its name suggests, it targets salamanders and newts. They may look more like lizards, but salamanders, like frogs, are amphibians, and the disease is starting to seriously affect them as well. (Newts are a type of salamander.)

In late 2014, a team of researchers led by An Martel of Ghent University in Belgium formally described the emergence of Bsal in Science Magazine and attempted to estimate just how severe an outbreak the world’s salamanders have to contend with. They verified that the pathogen is limited to salamanders, which at least means that frogs and toads don’t have to worry about yet another deadly pathogen. They suspect that Bsal first evolved in association with its salamander hosts in Asia and has probably existed there in a wildlife reservoir for at least 30 million years. Several Asian species that the team tested don’t succumb to the disease, which supports the reservoir hypothesis. They calculate that Bsal and Bd probably diverged from each other some 67.3 million years ago, each going on to infect its own set of amphibians.

Since Bsal has not historically been distributed continuously throughout the world, its spread from Asia to Europe – and thus the transition of the disease to outbreak status – was likely our fault. Amphibians, their eggs, and their parasites get moved around the world thanks to the nursery trade, but the Science study instead drops their blame on the international pet trade. Hundreds of thousands of Asian salamanders and newts move around the globe on an annual basis thanks to herpetology enthusiasts. Indeed, more than 2.3 million individuals of a single species, Cynops orientalis, the Chinese fire belly newt, were imported into the United States between 2001 and 2009.

“Our study demonstrates that the process of globalization with its associated human and animal traffic can rapidly erode ancient barriers to pathogen transmission, allowing the infection of hosts that have not had the opportunity to establish resistance,” wrote Martel.

That’s why the Center for Biological Diversity and Save the Frogs! petitioned the US Department of the Interior (which oversees the US Fish and Wildlife Service) last week to place an emergency moratorium on the import of salamanders and newts into the United States. They say that Bsal has already severely impacted fire salamanders in the Netherlands and Belgium, and they worry about possible impacts that Bsal could have on New World amphibians as well.

Indeed, Martel’s team verified that New World species are susceptible to the disease. It’s especially threatening for the eastern newt, a species found in 33 US states. And some conservation activists also fear that the striped newt, a species that’s been a candidate for Endangered Species Act (ESA) protection since 2011, could be wiped out entirely if the disease spreads to the US. While the disease has spread through Northern Europe and the UK, more than 180 samples taken from eastern US salamanders have so far been negative for the pathogen.

While it isn’t one hundred percent certain that the pet trade is to blame (the Bsal fungus could also be wind-borne or transported by migrating birds, though those vectors wouldn’t sufficiently explain why the disease has only recently begun to spread across the globe), the authors of the petition argue that the US is a global hotspot for salamander biodiversity, with some 190 species, more than any other place on Earth. Twenty of those species are already listed on the ESA, with an additional three (including the striped newt) listed as candidates, and a whopping 37 awaiting listing decisions from the US Fish and Wildlife Service.

“The available data show that if Bsal is allowed to enter the United States it is likely to have fatal impacts on native species and it will be nearly impossible to stop its spread,” they write. “Bsal’s introduction would have devastating impacts, with likely massive salamander die-offs, population extirpations, and species extinctions across the United States.” – Jason G. Goldman | 20 May 2015

Sources:
Petition to institute an emergency moratorium on imports of all live salamanders and to list all live salamanders in trade as injurious under the Lacey Act unless free of batrachochytrium salamandrivorans (PDF)

Martel, A, et al. (2014). Recent introduction of a chytrid fungus endangers Western Palearctic salamanders. Science, 346(6209), 630-631. DOI: 10.1126/science.1258268.

Header image: Eastern Newt; Durham County, North Carolina, United States, via Wikimedia Commons/Patrick Coin.

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