In the remote jungles of eastern Panama, a frog-killing fungus that has decimated some 200 species of amphibians globally is zeroing in on some of its last targets.
The likely demise of frogs there, including the bright orange Atelopus certus is ultimately attributed to human activity, illustrating man's harmful impact on the planet.
Below are details about frog chytrid and why it matters.
WHAT IS FROG CHYTRID?
Frog chytrid is a bacteria called Batrachochytrium dendrobatidis, or Bd. It causes a disease called chytridiomycosis on some amphibians. Infection interferes with vital skin functions including hydration, body temperature control, electrolyte balance and respiration. Advanced infection kills by cardiac arrest.
"It's so fast and so dramatic the way it just kills them outright," said Robin Moore of Conservation International.
Scientists still do not know exactly where frog chytrid originated - it was described in 1998 well after it had spread to different corners of the globe - but theories trace it to trade in chytrid-carrying frogs resistant to Bd.
Once present, the fungus fans out gradually. A recent study showed it arrived in Panama via Mexico at some point after 1970. As soon as it strikes a susceptible amphibian population, a massive die-off can be witnessed in a season.
CAN IT BE STOPPED?
Scientists say there is probably no way to stop chytrid's spread. The only surefire way to save endangered species is by maintaining breeding populations in captivity, which has required scientists to overcome complex husbandry hurdles. The Panama City-based Smithsonian Tropical Research Institute and the Houston Zoo are leading international efforts in Panama.
Only a few highly endangered frogs appear to have survived. An ongoing experiment in San Francisco State University last year found yellow-legged frogs bathed in a chytrid-fighting bacteria survived Bd's arrival last summer.
Those not bathed in the bacteria died.
In Ecuador, scientists found an Atelopus species not seen since 1995 as part of a Conservation International global project to locate 100 "lost" amphibians. The discovery was encouraging, but only four of the 100 on the list were found.
Scientists are working to discover how the Rio Pescado stubfoot toad, or Atelopus balios, resisted chytrid. "It was a huge discovery," said Moore. "These ones that are hanging on could provide the silver bullet."
While many species of amphibians may have been wiped out before Bd's arrival, scientists point to the small pocket of Panama as well as Madagascar, Sri Lanka and Papua New Guinea -- which are believed to be chytrid-free -- as a chance for scientists to mitigate what they consider the fungus' inevitable arrival to all susceptible corners of the planet.
WHY DOES IT MATTER?
Chytrid helps to illustrate what some scientists are calling the Anthropocene, a period of geological time marking mankind's adverse impact on the planet that likely began with the Industrial Revolution.
The discussion may still take a couple of decades, while scientists examine the extent to which humanity's effects on the Earth will register permanently on the geological record.
Widespread extinctions of life forms, the global spread of invasive species, rising sea levels, climate change and human population growth are all considered contributing factors. More than 40 percent of the world's 6,000-plus amphibians are declining due to pollution, habitat loss and chytrid.
"The variety and diversity and uniqueness of these changes really do suggest it's quite a significant turning point," said Jan Zalasiewicz, a geologist at the University of Leicester in England. "I still almost have to catch myself in disbelief that such a profound and unique set of changes is going on."
(Reporting by Sean Mattson)