Previous research has shown that altering or reducing the skin microbiome leaves amphibians more vulnerable to chytridiomycosis infection, she says. Whether by competing for space, or by providing antimicrobial compounds, the skin microbiome is probably protective.
Moreover, amphotericin B is much less toxic to frogs than is itraconazole.
Rollins-Smith suggests that a more benign cure for chytridiomycosis might involve treatment first with amphotericin B, followed by itraconazole, which would enable a lower, less toxic dosing with the latter.
"That makes sense," says Gratwicke. "It would also correspond with my field observations."
Chytridiomycosis is a skin disease. Clinical signs include reduced appetite, weight loss, lethargy, and loss of righting reflex. Death is thought to result from disruption of sodium and potassium ion transport in the skin, resulting in osmotic imbalance and asystolic cardiac arrest.
Gratwicke and others hope eventually to be able to cure chytridiomycosis with probiotic treatments that would add protective bacteria to the skin. But such efforts have yet to bear fruit. B. dendrobatidis was first identified as a threat to amphibians in 1998.
There are about 7,000 amphibian species in the world, including roughly 6,000 frogs, 600-700 salamanders, and about 200 caecilians, says Gratwicke. The International Union for Conservation of Nature lists 122 "missing" species of frog, on its "red list," most of which are likely extinct, including 90 for which chytridiomycosis is listed as the essential threat. Some salamanders and caecilians are also endangered. (Caecilians are legless borrowing creatures that look like the progeny of a mating between a snake and a worm).
|Contact: Jim Sliwa|
American Society for Microbiology