By Jason
Bittel 3/28/19 Washington Post
There is a
plague ripping through the amphibian species of the world. It’s caused by
fungus that’s invisible to the naked eye and spreads easily by many means. It
kills by disrupting the way these creatures breathe through their skin,
essentially suffocating frogs and salamanders.
The disease
is called chytridiomycosis, and according to a landmark study published
Thursday in the journal Science, it’s even worse than we thought.
Scientists
once estimated that about 200 species of frogs and salamanders have been harmed
by the disease, but the study concludes that chytrid fungus has contributed to
declines in at least 501 amphibian species. Ninety of the species are thought
to have gone extinct because of it. Populations in tropical Australia, Central
and South America seem to be hardest hit, though populations in Africa, Europe
and North America are also affected. According to this accounting, the epidemic
has caused the worst loss of biodiversity of any disease ever recorded.
“It’s a
staggering thing to consider,” said Jonathan
Kolby,
one of the study’s authors and a herpetologist specializing in conservation and
wildlife diseases at James Cook University in Australia. “We’ve never before
had a single disease that had the power to make multiple species extinct, on
multiple continents, all at the same time.”
Carly Muletz
Wolz, a
molecular pathogen scientist at the Smithsonian National Zoo’s Center for
Conservation Genomics, said she was not surprised by the findings and that it
was important to finally see the scale of the problem quantified.
“This is the
newest, best estimate on where things stand,” said Muletz Wolz, who was not
involved in the study. “And it’s probably even worse than this, because you
only know what you know.”
The scope of
the chytrid fungus’s onslaught on the amphibian world is unprecedented. West
Nile virus, now a relatively well-known pathogen, affects just 23 bird species.
The fungus laying waste to bat populations across North America, white nose
syndrome, is attacking about a dozen species.
“You’ve got
hundreds if not thousands of frog species that could go extinct, and they’re
getting much less attention from a global health perspective,” said Kolby, who
helped establish the Honduras
Amphibian Rescue and Conservation Center.
Scientists
suspect the lineage of the chytrid fungus that has been ravaging frog
populations became more virulent in the 1980s, after it hybridized with another
lineage. As more people transport infected amphibians in the global pet trade,
the more opportunity there is for the fungus to spread and further hybridize
“There’s
nothing preventing hybridization from happening again, and if it happens again,
who knows what that hybrid offspring will act like,” Kolby said. “We could have
another global wave of disease, which could be similar, different or even worse
than the one we’re facing now.”
In 2013,
scientists discovered a species of chytrid that goes after salamanders, called
Batrachochytrium salamandrivorans. Fortunately, this species has not yet made its
way into the United States. In 2016, the U.S. Fish and Wildlife Service made it
illegal to import 201 high-risk species of salamander as a safeguard against
outbreaks.
There are no
such restrictions in the frog trade.
Kolby said
the United States and other countries need to enact stricter biosecurity
measures for several reasons. It’s already
been shown
that frogs and toads can harbor the fungus that afflicts salamanders, so only
banning certain salamander species may not be enough to protect native species.
In many
ways, the United States already does a good job of preventing the spread of
diseases that affect crops and livestock, Kolby said, thanks to agencies such
as the Agriculture Department and the Centers for Disease Control and
Prevention. Chytrid fungus may have slipped through the cracks, however,
because it does not immediately affect humans.
“What
concerns me is there’s going to be a next time. By not using this as a learning
experience about what happens when we aren’t being careful, it almost
undoubtedly ensures that the wildlife trade is moving other pathogens right
now, be it for mammals, birds, fish. You name it,” he said.
It is unclear
how a global amphibian decline will disrupt the various ecosystems they
inhabit. Many species improve water quality by clearing waterways of vegetation
when they are in the tadpole stage of development. Other frog species play a
crucial role in keeping mosquito numbers in check by feasting on their larvae.
And countless other species rely on frogs as a food source.
Even though
the outlook is darker than it’s ever been, glimmers of hope exist. Kolby and
his co-authors were able to find documented population trends for 292 frog
species that have seen declines because of chytrid. Of those, 60 species have
shown some evidence of recovery, possibly because they evolve to resist the
fungus. The scientists note, however, that these recoveries are mostly of individual
populations, rather than rebounds for the species at large.
“It at least
gives us something to look at in terms of why some species are recovering and
why others are not,” said Muletz Wolz.
Kolby said
he can understand how the news fuels a sense of hopelessness.
“But I think
that’s the worst thing that could come out of this,” he said. “I still look at
this as just one huge opportunity to learn how to not let this happen again.”
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