New Disease Emerges as Threat to Salamanders
The invasive chytrid fungus is spreading in Europe; new policy could prevent its introduction in the United States.
The death knell for the fire salamanders of the Netherlands offers a sharp warning about the ecological risks of pets as invasive disease vectors. A study published in Science in October shows that the salamanders succumbed to a type of chytrid fungus, which causes a disease known as chytridiomycosis, that originated in Asia; the pathogen, called Batrachochytrium salamandrivorans, can be transmitted by some Asian salamanders and kill susceptible species within two weeks. More than 2.3 million Chinese fire belly newts, one potential reservoir for the disease, were imported into the United States between 2001 and 2009. The disease is lethal to 12 of the 17 non-Asian salamander species tested.
The pathogenic chytrid fungi are disquieting examples of how quickly an invasive disease can decimate an entire class of the tree of life. More than 200 amphibian species have gone extinct already due to a related pathogen that emerged in the 1990s, B. dendrobatidis.
The new invasive chytrid showed up in the Netherlands in 2010 when volunteers in an amphibian monitoring program looked for fire salamanders in the country’s three wild populations and returned with barely any: The population had experienced a 96 percent decline, and no one knew why. Because it was so sudden, ecologist Annemarieke Spitzen-van der Sluijs of the NGO Reptile, Amphibian, and Fish Conservation the Netherlands knew that she had either a chemical spill or disease outbreak on her hands. She sought the help of wildlife disease veterinarians An Martel and Frank Pasmans of Ghent University, Belgium, who tested the specimens for all known causes of such dramatic amphibian declines and came up with null results.
The remaining 150 or so Dutch-origin fire salamanders were kept in captivity, but they also began dying. As Martel performed necropsies, she noticed microscopic fungal growth in skin lesions typical of the known chytrid fungus. “Because the fungal organisms looked very similar to B. dendrobatidis but the tests for it were negative, we knew that this was a new species,” she says. She and her colleagues published these results in Proceedings of the National Academy of Sciences of the U.S.A. last year. Their new study in Science, led by Martel and Pasmans, reveals the origin and current distribution of the new chytrid fungus B. salamandrivorans, as well as the susceptible and reservoir species among the more than 5,000 amphibian individuals from around the world that they tested.
The new chytrid disease has not been detected in the Americas yet. Karen Lips of University of Maryland, who is a coauthor on the Science paper and an expert on chytrid fungus, wants to keep it that way. She, along with several US-based conservation NGOs, is pushing for tighter controls on the pet trade to prevent the otherwise inevitable spread of the disease to the United States. According to this new study, two common salamanders of North America, the red-spotted newt in the east and the rough-skinned newt in the west, are susceptible to the new chytrid disease. “All evidence says if it gets here and escapes into the wild, it’s going to spread all over North America,” says Lips. “Even though most of our North American salamanders were not tested, if you look at the phylogenetic tree, it suggests that at least some of them are going to be susceptible to this disease.”
North America has the highest diversity of salamanders in the world, with hotspots in the southern Appalachian Mountains. Lips says that about 50 percent of North America’s salamanders are already threatened. This new disease could push many of these species toward or over the brink of extinction.
“In this day and age, our biggest threats are emerging infectious diseases. But, officially, there’s no way the United States has to require anybody to show that their imports of live animals are clean, and they have no legal tool to prevent that introduction,” declares Lips. “We’re not only blindfolded, but our hands are tied as well. It’s only a matter of time before one of those infected animals is imported, and either escapes or is released.” The US Fish and Wildlife Service (FWS) holds the key to regulating live animal imports that could affect wildlife, but Lips says current legislation needs updating to deal with emerging infectious diseases.
The Invasive Fish and Wildlife Prevention Act, a proposed bill awaiting congressional approval, would give the FWS more control over monitoring and regulating invasive fish and wildlife and their diseases. Another amendment could also address the threat of B. salamandrivorans: Under the Lacey Act, a law regulating the trade of live organisms, FWS can regulate the importation of foreign amphibians, if they are deemed “injurious to human beings, to the interests of agriculture, horticulture, forestry, or to wildlife.”
Lips and many researchers and conservationists would like the FWS to allow the import of salamanders only if they are shown to be free of such lethal invasive disease. Under Title 50 of the Lacey Act, the FWS has passed such measures for imported trout and salmon after several viruses posed a threat to domestic fish. Similar legislation to prevent spread of the first chytrid disease was proposed by the Defenders of Wildlife, a conservation-oriented NGO, in a petition in 2009, but the legislation has not moved forward.
In response to an emailed inquiry about Lips’s points, FWS public affairs specialist Laury Parramore stated: “The Service is very concerned about the potential mortality the salamander chytrid could cause. The United States has more salamander species than any other country, and many are already federally listed as endangered or threatened. The Service takes this issue seriously and is looking at various options under our authorities, but we have not yet completed our review.” To prevent the introduction of this invasive disease, Lips and those at FWS think that policy and science need to be proactive.
Meanwhile, the new salamander disease has already spread from the southern Netherlands to Belgium. Martel explains, “The first outbreak was discovered in the Netherlands in 2010 and lasted until 2012. Then, at the end of December 2013, we had the first outbreak in Eupen, Belgium, which is approximately 30 kilometers south from the first outbreak. Then, in April this year, we had the third outbreak in Robertville, Belgium, which is again about 30 kilometers south. If the disease continues to progress at the same rate, which we expect because there are no natural barriers in Europe to prevent it, then in about 25 to 50 years, all the salamanders in Europe will be affected.”
The remaining 150 Dutch fire salamanders are surviving in captivity, but there currently is no funding for a captive breeding program. The researchers do not want to release them back into the environment until the disease is gone from the outbreak areas, a situation they are monitoring now. According to Martel and Spitzen-van der Sluijs, they do not know yet how to slow the spread of the disease, but preventing further introductions through the pet trade will keep the pathogen from spreading even more quickly.
Although some treatments have been proposed for the first chytrid fungus, B. dendrobatidis, such as immunization protocols and probiotics, none have been sufficiently tested in the field. Perhaps insights gained from the first chytrid disease will accelerate research on the second, but at present very little is known about the basic biology of B. salamandrivorans or how it compares to B. dendrobatidis. Without fast and strategic action, the new chytrid disease could exacerbate worldwide amphibian declines and extinctions, especially for salamanders.—Katie L. Burke