Bd favors frogs, while Bsal prefers salamanders, but both fungi produce the same, brutal disease called chytridiomycosis. When spores of either species attach to a susceptible amphibian, which number in the hundreds, they harvest its skin cells to produce a so-called mother cell that generates even more spores.

This is a nightmare for these animals, which famously use their skin to take in water and, in some cases, breathe.

“Grossly, you’ll see these ulcers being created on the skin,” says Matt Gray, an ecologist at the University of Tennessee, who has been studying the genus Batrachochytrium for years. “It looks like somebody has taken a cigarette butt and burned the animal. Ultimately, it causes disease and death.”

When Bd was discovered in 1998, it was already spiraling into a pandemic, infecting streams and ponds from South America to Australia and, of course, the animals that call them home. Now scientists fear Bsal is headed down the same path — this time at the expense of what could be hundreds of salamander species.

Bsal is native to Asia, scientists believe, where it lives in relative harmony with local amphibians that likely co-evolved with the pathogen over millennia. But sometime earlier this century, Bsal apparently hitched a ride to the Netherlands through the pet trade. There, it escaped into the wild, where it thrived. In a matter of years, Bsal wiped out nearly 96 percent of the country’s native population of fire salamanders.

An infected fire salamander (Salamandra salamandra) covered in small, deadly Bsal ulcerations. Scientists believe the pathogen has nearly wiped out fire salamanders in the Netherlands. Photo by F. Pasmans

Scientists say it’s only a matter of time before the fungus travels the same route to the U.S., home to the world’s largest number of salamander species, more than half of which may be susceptible to Bsal infection, according to Gray’s unpublished research. Not even a restriction recently placed on the pet trade — a ban on the import of 201 species that scientists believe to be susceptible — can stop it, they say.

“It really does seem to be a matter of when and not if,” says Priya Nanjappa, the former national coordinator for the nonprofit Partners in Amphibian and Reptile Conservation (PARC), one of two nonprofit groups addressing the threat of Bsal in the U.S.

Like other amphibian experts, Nanjappa is worried. But she points out an important silver lining: Scientists, possibly for the first time, have advanced notice of the emerging threat. They know Bsal is coming, they know what to look for, and, thanks to decades of research on Bd, they have a good idea of how it will spread. So instead of waiting to be caught off guard by an outbreak, they can proactively search for the fungus — and pounce when they find it.

The path of a pathogen

No matter how much time you have, finding Bsal isn’t easy. Salamanders may be difficult to spot on a hike, but they’re incredibly widespread, hiding under logs, in mud and water in New York, California, and every state in between. Then there’s the pathogen itself. There are dozens of ports along the coast into which pet amphibians are imported and thousands of pet stores. Where to even begin?

For all that we don’t know, there’s a lot we do: the distribution of salamander species, the location of pet stores, the quantity of live amphibians imported into different ports. We even know the temperatures in which Bsal can thrive (15 to 20 degrees Celsius, or 59 to 68 degrees Fahrenheit). With data, you can build models. And with models, you can guess where Bsal is most likely to be introduced.

In 2016, researchers from the U.S. Geological Survey (USGS) did just that. Using geographic data on the pet trade, salamanders and the pathogen, they built a series of heat maps showing where Bsal is most likely to enter the U.S. and where salamanders will likely experience the most dramatic declines.

Heat map of the U.S. showing the total relative risk of Bsal to native U.S. salamanders based on the introduction and consequences assessment published in the journal Royal Society. Figure from Richgels, et al., 2016, via CC BY 4.0

Deep red pixels were concentrated in Florida, Southern California and New York, epicenters of the pet trade. Their maps also showed dark hues in the Appalachian Mountains and Pacific Northwest, where species diversity is greatest.

When Bsal arrives, that’s where it will most likely show up, they reasoned. Now they just had to go look for it.

The search begins

Two decades of research on Bsal’s cousin, Bd, has its advantages. For one, scientists know how to quickly test amphibian skin for different species of fungi. It’s like identifying the killer at a crime scene: When researchers come across a salamander in their search, they collect material on its skin, run a DNA test, and look for a match in their database of deadly fungi, which now includes Bsal.

“You take a swab and rub it along the skin of the animal,” says Dede Olson, an ecologist at the U.S. Forest Service. “The fungi comes off on your swab, and then you run the genetics on that swab to see what you found.”

It’s with this method that USGS researchers traveled to the darkest reds on the map in 2016 to begin testing salamanders — a whopping 10,000 of them. If Bsal was present in the U.S., surely they’d be able to find it.

Robert Fisher is part of the team in Southern California that was responsible for collecting around a quarter of the samples. “We’re close to LAX, which is where most of the Asian salamanders are coming through,” says Fisher, a biologist at USGS. “Whether Bsal has jumped from the pet animals to wild animals is the crux of this surveillance.”

With tools for genetic analysis, finding Bsal is only as hard as finding its wet-bodied hosts — which can be difficult, even though they’re widely distributed.

You’re often standing “chest-deep” in pond water, fighting back mosquitos and flies, says Daniel Grear, a colleague of Fisher’s who leads the surveillance effort at USGS. “Usually it depends on having a team of people with fine mesh nets walking around a pond to where we think the newts are going to be.”

A USGS researcher looks for eastern newts (Notophthalmus viridescens) in a pond in Dane County, Wisconsin.

And searching on land isn’t much easier. “They’re really hard to find because they live in burrows,” Fisher says of L.A.’s slender salamanders. “When we started the surveillance, it was so dry. By the time we got the sample kits [to swab the salamanders] it was really hard to get good numbers of them.”

The USGS team persisted, swabbing salamander after salamander. Meanwhile, another search for Bsal was underway, in tanks and terrariums across the U.S.

Wild amphibians tell only half the story. Or at least that was the thinking behind a project led by Blake Klocke, a scientist at George Mason University, designed to sniff out Bsal in the pet trade. In 2014, Klocke asked salamander owners across the country to swab their cold-blooded pets at home and mail the samples to a lab for diagnosis.

Two years later, he had 639 swabs representing 65 species, most of which were susceptible to Bsal. Now he just needed to run the genetic tests.

Scientists hold their breath

Last December, USGS researchers swabbed their 10,000th salamander. After analyzing the final sample, they sighed in relief and discarded the Q-tip-like swab, as they did with thousands of others.

“We didn’t detect it,” Grear says. “If Bsal was present and widespread in any area we sampled we would have detected it — we think. Overall, our confidence that it’s not here and not widespread has increased.”

Results from Klocke’s study on pet salamanders were equally favorable: Nobody’s pet tested positive for the pathogen (though some of them did register positive for Bd, which the researchers also screened for).

“Bsal has not been detected to date in captive collections or in wild populations in the U.S.,” the authors wrote. “Our results suggest that if Bsal is present in private captive U.S. salamander collections, it occurs at extremely low prevalence.”

Great news, right? Yes, Grear says, but he’s quick to mention that the results are not definitive.

“10,000 is a lot of samples, but there are still a lot of areas that we couldn’t assess,” he says. “There’s still a chance that it’s here.”

Plus, they do nothing to change the outlook for American salamanders, he adds. No matter how confident scientists are that Bsal is bound to Europe and Asia by the ocean, there’s always a risk of introduction. And so there’s always a need for surveillance.

The search continues

Since the USGS study, salamander surveillance has died down, Grear says. Monitoring amphibians takes an enormous amount of resources, and after the study failed to turn up Bsal, much of the attention to the threat dried up.

“There’s been nothing quite as extensive as what we did,” Grear says. “It’s [a lack of] resources, money and attention to it.”

That doesn’t mean there aren’t scientists up to their waist in pond water searching for fungus. Several government organizations, including the National Park Service and state wildlife agencies, have ongoing amphibian monitoring programs. For them, searching for Bsal simply means adding the fungus to the existing slate of diseases for which they already screen.

“It coincides with our normal monitoring,” says Lori Williams, a biologist with the North Carolina Wildlife Resources Commission. “We go out into the field and swab for two kinds of chytrid fungus now.”

A green salamander is swabbed for the presence of Bsal. The procedure is relatively uninvasive, and the subjects are generally released unharmed. Photo courtesy of the North Carolina Wildlife Resources Commission
A researcher swabs a juvenile eastern newt (Notophthalmus viridescens), which is in its vibrant, land-dwelling “red eft” stage of development. Photo courtesy of the North Carolina Wildlife Resources Commission

National parks like Great Smoky Mountains are also monitoring their amphibians for disease, says Tracy Thompson, a veterinary medical officer with the National Park Service. “We have great parks that are watching their reptile and amphibian populations,” she says. Over the next several months, she’ll be helping them prepare a Bsal surveillance plan, especially those in regions at greatest risk to invasion.

Even outside government initiatives people are in pursuit of the pathogen: independent scientists, graduate students and, in one case, a concerned high schooler, Olson says. “Anyone that’s concerned can do surveillance,” she says. “We kind of have recipe books on how you collect samples.”

The general public was also called on to help search. In the summer of 2017, Partners in Amphibian and Reptile Conservation (PARC), a program run by the Department of Defense, launched an email-based alert system that allows anyone to report sightings of sick or dead salamanders.

“We want reports of apparently sick, dying or dead animals with disease signs,” Olson said in a press release announcing the alert system. “It would help if the greater community of nature enthusiasts and recreationists would report their observations of disease events, as these can be cryptic and go unnoticed.”

So far, they’ve only received a dozen or so reports, Thompson says, perhaps because few people regularly encounter salamanders, let alone are familiar with the alert system or the threat of Bsal. None of them were verified cases of Bsal.

Forest Service staff are also combing through photos submitted to the citizen science platform iNaturalist, Olson says, which visually captured tens of thousands for North American salamanders “We’re looking to see if anything falls under the category of disease,” she says.

An uncertain outlook

Still, many scientists question whether the current search effort is adequate. The range over which Bsal could emerge is simply too expansive, they say, and there just aren’t enough eyes on the ground. Or eyes on the ground that are keenly perceptive to Bsal’s effects.

“Unlike in human health, where we have all of these hospitals paying attention to something new, the chance of catching the first outbreak of Bsal is almost zero,” says Katie Richgels, a biologist at the USGS and lead author of the heat map study.

Gray agrees: “The likelihood of someone seeing it, reporting it, and confirming that it’s Bsal … it’s a huge sequence of events, so the chance of it entering [and being] detected is low. By the time we figure out it’s here, it will probably have already been in the system for a while.”

Even if we do, out of luck, find the pathogen when first it arrives, Richgels says, it’s still unlikely that we’ll be able stop an outbreak. As she and other scientists point out, there’s no cure and no treatment for a diseased population. “In my honest opinion, if it gets here, it’s spreading, and we’re looking at catastrophic losses of a couple of species or more,” she says.

This raises an important question: Is resource-intensive surveillance even worth the effort if scientists can’t stop Bsal’s spread when it arrives?

Without a doubt, Grear says. While the spread of Bsal can’t be thwarted altogether, it can be slowed, he says, such as by dumping antifungals into a pond or quarantining infected habitats. These efforts buy researchers time: time to learn more about the disease; time, perhaps, to develop a cure. But they’re only effective if you know where to use them.

Pinpointing the pathogen also gives scientists a better shot at saving the most at-risk species, Grear says. With the USGS heat maps, for example, scientists can predict the likely route Bsal will take when it lands on American soil. If critically endangered salamanders are on its path, researchers can move them into captivity before the pathogen arrives.

Such a maneuver would be extreme, Grear says, but it highlights what makes the threat of Bsal so unique among wildlife diseases: Days, months, or even years before the pathogen arrives, scientists are calculating different response strategies that are informed by in-depth studies.

“With Bd, the science community was measuring the impact after the fact, assessing how much damage it was doing while it was spreading,” Grear says. “Here, we’re getting baseline data so that multi-agency groups are better prepared to take action. That’s unique and positive in the world of wildlife diseases.”

It’s precisely this preparedness that gives many scientists hope that salamanders may not face the same fate as frogs and bats (which are battling their own fungal plague).

“We are more alert than we ever have been for any other wildlife issue previously,” Olson says. “I’m hopeful.”

 

 

Banner image: A fire salamander (Salamandra salamandra). Photo by Christian Jansky via Wikimedia Commons (CC BY-SA 1.0)

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Article published by Morgan Erickson-Davis
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