Asian fungus threatens salamanders: lethal pathogen is spreading through the global pet trade.
The fungus, nicknamed Bs, for Batrachochytrium salamandrivorans, came to the attention of scientists during baffling die-offs of rare fire salamanders in the Netherlands. Another Batrachochytrium species, B. dendrobatidis, or Bd, has ravaged amphibian populations in recent decades. But An Martel of Ghent University in Belgium and her colleagues ruled Bd out in the Netherlands die-offs and discovered that the culprit was an unknown relative, which researchers named last year (SN: 10/5/13, p. 18). Now, after more surveys and lab tests, Martel and collaborators have started to answer questions in the Oct. 31 Science about the spread and targets of Bs.
"It is appropriate to be exceptionally concerned, if not alarmed," says Jamie Voyles of New Mexico Tech in Socorro, who studies the killing mechanisms of the other Batrachochytrium fungus. So far, no evidence shows the newly recognized disease has reached North America, home to a quarter of the world's known salamander species. But the continent is a market for amphibians from Asia, and as veterinary pathologist Allan Pessier of San Diego Zoo Global puts it, "we need to focus on disease screening and biosecurity for imported animals."
This new salamander pathogen came as a shock to biologists already dismayed by more than 20 years of amphibian disease outbreaks. In 1999, Pessier and others identified that Bd, a chytrid fungus, was the cause. Generally mild-mannered, chytrids usually break down dead stuff in the environment.
The second killer chytrid, Bs, seems to target salamanders, Martel and colleagues report. The team attempted to infect 35 species picked from different branches of the amphibian genealogical tree. The fungus seemed unable to attack frogs, toads or legless snake-shaped amphibians called caecilians. But it quickly killed 41 of the 44 individual salamanders tested from Western temperate-zone species.
"It's not a pleasure to see," Martel says. In a susceptible species, the fungus "literally eats the skin off an animal."
In the infection tests, Asian species were more resilient to Bs, suggesting the fungus originated in Asia, the researchers say. Asia also looked like the probable origin after the team's epic efforts to check for pathogen DNA on 5,391 wild amphibian specimens worldwide. Bs turned up on only two of the four continents surveyed. Animals tested positive in Thailand, Vietnam and Japan, where biologists have not reported salamander die-offs. These species may have evolved for millions of years with the pathogen. Bs was also detected in the Netherlands and Belgium, where wild salamanders have died.
The new study makes a good case for an Asian origin of Bs, says Timothy Y. James of the University of Michigan in Ann Arbor and a coauthor of a massive genetic study of the Bd fungus.
To see if an Asian disease could travel via the global trade in live animals, Martel and colleagues checked skin samples from 2,335 captive animals in such places as European pet shops, a Hong Kong export business and London's Heathrow Airport. Three salamanders in the sample, two of which were sent to Europe in 2010, carried the fungus. Lab tests with two other species show that one salamander touching another can transmit the disease, the researchers report.
No wild North American salamanders have tested positive for Bs, although surveys so far have big gaps, says study coauthor Karen Lips of the University of Maryland in College Park. She warns that if the disease does strike North America, the inner workings of ecosystems could change. Tiny salamanders darting through leaf litter or burrowing into soil often get overlooked, but "these things are superabundant," she says.
She fears a repeat of the nightmare she chronicled in Panama in 2004 as the first amphibian-killing fungus swept through. Bd exterminated some 30 of 74 amphibian species at her study site and shook up the rest of the community, even reducing numbers of certain snakes that eat amphibians.
To prevent such loss and disruption, Lips calls on Congress to pass proposed legislation requiring health checks for imported amphibians. Regulations already address keeping crop plants and livestock from bringing new disease into the United States, she points out.
Caption: Skin lesions on the face of a fire salamander show the ravages of a chytrid fungus species discovered last year, now suspected of escaping from Asia.
Please note: Illustration(s) are not available due to copyright restrictions.
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|Title Annotation:||LIFE & EVOLUTION; Batrachochytrium salamandrivorans|
|Date:||Nov 29, 2014|
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