Over the past few decades, biologists have been watching in horror as a deadly disease has swept the globe, devastating amphibian populations and causing many species to go extinct. Caused by a fungus, scientists have now finally been able to identify its origin, revealing it likely emerged in East Asia before being spread around the planet by the international pet trade.
The disease, known as chytridiomycosis or chytrid for short, is caused by a highly infectious and frequently deadly strain of fungus that has wiped out not just entire populations of frogs and toads from the Amazon to the Mediterranean, but whole species. Its impact on the environment and the planet’s biodiversity cannot be understated.
With no effective cure or treatment for the disease, in many cases the only course of action is to bring threatened frogs into captivity and keep them as an insurance population should their wild relatives not pull through. Because of its severity, finding out the diseases’ origin has been of high priority to better understand where it came from and in turn how we might be able to treat it.
Chytrid is caused by a fungus called Batrachochytrium dendrobatidis, frequently shortened to just Bd. By carrying out a genetic analysis of samples of Bd collected from all around the planet, the team of researchers were able to construct a detailed map of the pathogen, and trace it back to where it likely originated, publishing their results in Science.
They found that there were four main lineages of the fungus, three of these found widely across most continents. But there was one stand-out strain that caught the team’s attention, which is found only in South Korea on native frogs.
The genetic diversity of this Korean Bd strain was much more diverse than that of the others, suggesting that it is of older origin, and most likely to resemble the ancestor to all other strains. It seems that the Korean Peninsula is ground zero for this amphibian plague.
“Biologists have known since the 1990s that Bd was behind the decline of many amphibian species, but until now we haven’t been able to identify exactly where it came from,” explained Dr Simon O’Hanlon, lead author of the study. “In our paper, we solve this problem and show that the lineage which has caused such devastation can be traced back to East Asia.”
They think that the deadly strain of Bd is incredibly recent, only appearing between 50 and 120 years ago. This coincides with the sudden expansion of global connectedness, and with it a boom in the pet trade. They suspect that patient zero is the Oriental fire-bellied toads native to East Asia, as it became increasingly popular as a pet.