Fatal
Frog Fungal Disease Figured Out
Electrolyte imbalance stops amphibians' hearts.
Nature News ^ | 22 October 2009 | Emma Marris
One may well remember just a few short years ago where it had been
declared that because of global warming frogs were dying out around the world
and the ecological armageddon that would sone swallow the rest of the earth –
Well here now is the results “A fungal disease” that has largely come and gone,
and no admission of wrong by the environmental mafia for crying wolf,
Posted on Friday,
October 23, 2009 8:00:37 PM by neverdem
Frogs
are suffering from a fatal fungal infection.Vance T. Vredenburg/SFSU
A fungal infection that is killing amphibians
around the world acts by disrupting the flow of electrolytes across their skin,
ultimately causing heart failure. The discovery is helping to raise hopes that
a treatment for the infection could one day be given to amphibians in the wild.
Batrachochytrium dendrobatidis, a kind of chytrid fungus that causes the skin disease
chytridiomycosis in amphibians, was likely spread around the world by the South
African clawed frog (Xenopus laevis) in the 1930s and
1940s, when the frog was widely used as a pregnancy test. A pregnant woman's
urine, injected under the frog's skin, would contain sufficient hormones to
make the animal ovulate.
But although the South African clawed frog seems
to have immunity to the disease, many other amphibians are not so lucky.
According to one study led by chytrid expert Karen Lips of the
Jamie Voyles, a disease ecologist at
Voyles and colleagues monitored the progression of
the infection, took blood and urine samples and measured electrolyte flow
across skin samples. They found that levels of two ions — potassium and sodium
— were greatly reduced in infected frogs, and that the ability to move these
ions back and forth across the animals' skin had been greatly impaired.
"Frog skin is really unique because it is
permeable to water but it must maintain proper concentrations of these
[electrolyte] ions," says Voyles. In infected frogs, "the electrolyte
balance is all out of whack".
The low potassium levels, in particular, were
probably responsible for a breakdown of the electrical regulation of the heart,
and the frogs ultimately died because their hearts stopped. The work is
reported in Science2.
The team found that an electrolyte-rich solution,
similar to sports drinks but more concentrated, delayed death in infected
frogs. But it couldn't cure them. "Because the skin is damaged, we can't
really keep them from dying unless we fix the problem in the skin," says
Voyles.
Although captive frogs can be bathed in an
antifungal medicine to rid them of their infection, there is no easy way to
treat the hundreds of species of wild amphibians at risk of being wiped out by
the fungus.
Voyles's work is just one piece of research that
might someday lead to a treatment that could be deployed in the wild.
Geneticist Erica Rosenblum of the University of Idaho in Moscow is looking at
gene expression in both the fungus and the host to determine what makes the
fungus so lethal — and why amphibian immune systems don't seem to be aware of the
infection.3
"Jamie has found that their osmotic regulation is all screwed up, they are
essentially having heart attacks," she says. "Mine is an earlier
question: why don't they have an immune response?"
One possible treatment is being pursued by Reid
Harris, a microbial ecologist at
Harris would first like to try the technique on
populations of frogs in captivity — so-called survival assurance colonies held
in zoos and other institutions awaiting the day when
they can be safely returned to the wild.
Despite all these advances, Lips says that she has
seen too many frog populations destroyed by the fungus to retain her optimism
about saving what is left. "I don't know that there is enough money going
to the right labs quickly enough to make a difference," she says.
"More governments and NGOs need to step up. I mean, we are losing half the
amphibians on the planet. And throwing amphibians into zoos is a short-term
solution. It doesn't solve any problems."