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Frog-Killing Chytrid Fungus Hits Rarely Seen, Wormlike Amphibians

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caecilian Don’t feel bad if you’ve never seen a caecilian, let alone don’t know how to pronounce the word. These rare, legless amphibians—which look like a cross between a worm and a snake—spend most of their time underground, far from the prying eyes of scientists and other humans. Although some of the 190 or so known caecilian (think “Sicilian”) species can reach massive lengths—1.9 meters in some cases—they are rarely studied and very little is known about them.

Here’s something we do know: Caecilians, like the frogs and salamanders to which they are related, are apparently now at risk from the deadly chytrid fungus Batrachochytrium dendrobatidis (Bd), which has already caused hundreds of amphibian extinctions around the globe.

This news of the chytrid fungus’s spread comes from scientists in England with the Natural History Museum and the Zoological Society of London, who caught more than 200 caecilians and tested them for Bd. The scientists traveled to five countries in Africa and South America and studied 29 different species. They found the chytrid fungus living in the skin on 58 individual caecilians, many of which later died from the infections. The results are detailed in the May 2013 issue of EcoHealth.

“The fungus was known to infect and potentially kill both the other major groups of amphibians, but we did not know if it definitively could infect caecilians in the wild, and whether it could potentially also kill them,” museum zoologist and lead researcher David Gower said in a prepared statement. “We now know both of these are the case, and so this potentially major threat needs to be taken into consideration in caecilian conservation biology.”

Bd is a particularly nasty fungus for amphibians. It infects and damages the skin, which amphibians use to breathe and absorb water. Once the fungus takes hold it causes a disease called chytridiomycosis, which is usually fatal. Although recent evidence shows that the chytrid fungus is probably more than 40,000 years old, its exact origins are unknown. The fungus probably didn’t start spreading around the world until sometime in the latter half of the 20th century. It has now been blamed for close to 300 amphibian species extinctions. By most estimates, as many as a third of all known amphibians now carry the fungus and face declining populations or even possible extinction as a result.

There is no known cure for Bd at this time nor do scientists know exactly how it spreads. Previous research has shown that the fungus often arrives in new areas via the commercial frog trade, which distributes the animals for uses as food, pets, dissection learning tools or pregnancy tests. It has even been shown to travel from pond to pond on the legs of birds. We already knew that the fungus can stay viable in water, but the new research into caecilians seems to indicate that Bd can also live in and spread via soil.

The authors of this study point out that the IUCN Red List of Threatened Species currently lists most of the 190 caecilian species as “data deficient,” meaning there is not enough scientific information to assess their conservation status. With chytrid now known to be present in these little-understood species, it may be time to learn what we can, while we can, before it is too late.

Photo: Geotrypetes seraphini, a caecilian from Cameroon that tested positive for the chytrid fungus. Courtesy of the National History Museum

Previously in Extinction Countdown:

John R. Platt About the Author: Twice a week, John Platt shines a light on endangered species from all over the globe, exploring not just why they are dying out but also what's being done to rescue them from oblivion. Follow on Twitter @johnrplatt.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Heteromeles 12:14 pm 05/22/2013

    There are two annoying parts here:

    –Not a lot of mycologists study chytrids, so there’s not a huge body of knowledge to draw on when dealing with them.

    –Glomalean fungi (which I worked on, which are also primitive fungi) are known to have bacteria living inside their hyphae, and I can hope the same is true for Bd as well.

    Not that I expect mycologists to work on amphibians without funding, but I’d strongly suggest blast searching Bd and its relatives for traces of bacterial and viral DNA, and then to see if there’s a way to infect Bd with a bacterium or virus that kills it slowly and/or (better) weakens it to the point where amphibians readily survive infection. The reason I’d prefer weakening Bd to a quick kill is that, with biocontrol, you don’t want to kill the host (Bd in this case) too quickly. Instead, you want the control agent to spread throughout the entire Bd population and suppress it while leaving the amphibians alive.

    Link to this
  2. 2. LizNeeley 12:31 pm 05/22/2013

    It’s hard hearing more bad news on the Bd front, makes me feel very grim. Think it’s important to acknowledge the emotional side of this science.

    Strongly suggest reading ecologist Karen Lip’s guest post: “What if there is no happy ending” She traces the history of discovering this epidemic, and how we move past frustration and hopelessness. In it she says,

    “I have been thinking about change and shifting baselines a lot recently, as I struggle to comprehend as everything – from frogs and fish, to bats, bees and forest trees – decline in number. I remind myself, “Nothing is as constant as change.” It’s inevitable. This is the most honest and most hopeful thing I can say: evolution happens. Life is resilient.”

    Link to this

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