Frogs around the globe are dying because of a fungus that can affect all amphibians and is said to be the worst infection of any vertebrate anywhere.
According to a new study published in the journal Science, the deadly fungus originated in the Korean Peninsula and only spread to other regions in the last 50 to 120 years.
It is now on almost every continent (Antarctica is the only exception). About 44 per cent of Alberta frog populations have this fungus. In B.C. more than 11 per cent of all amphibians sampled showed evidence of the fungus, and those rates are only growing.
In order to understand how the fungus evolved to be such a potent pathogen, it’s essential to know where it originated. The team from the University College London and collaborators around the world sampled all the frogs they could find looking for evidence of the fungus. Once they had over 200 samples, they analyzed the data.
“We constructed what’s known as a phylogenetic tree, so we were looking at the population structure. And that revealed to us these genetic lineages that exist in the world,” said Simon O’Hanlon, lead author and research associate in the Department of Infectious Disease Epidemiology at the Imperial College London.
“From our research, what we found was [an] extremely high diversity of isolates of this fungus that are native to the Korean Peninsula. So these isolates showed at least twice as much genetic diversity as any other genetic lineage of this fungus in the world.”
Fungus digests the skin of frogs, impairing their ability to breathe
The fungus, called Batrachochytrium dendrobatidis, or Bd for short, grows on the skin of amphibians and releases enzymes called proteases, which effectively digests the skin. The effects are especially problematic because frogs rely on their skin to breathe when submerged in water. If the integrity of the skin is compromised, they can’t regulate their water balance or oxygen intake, and that eventually leads to heart failure.
This fungus also seems to be very well adapted to infecting most of the 6,000 amphibians on the planet, making it a risk to all frogs, salamanders, newts and any other amphibian.
However, while the fungus is native to the Korean Peninsula, it isn’t deadly to the native species. It’s not clear if it’s the fungus strain that isn’t quite as deadly or if the frogs that live there are used to living with the threat and have adapted to it. But once frogs who haven’t lived with it come in contact with the fungus, it is that much more deadly.
Impact of ‘worldwide loss of amphibian biodiversity’ still unknown
Frogs are a sentinel or indicator species, meaning they live on land and in water and can be affected by the toxins and deadly pathogens that exist everywhere in the environment. This makes them particularly useful for research, as scientists use them as an indicator for the health of ecosystems.
Amphibians are a major source of food for reptiles and birds, and they’re also very good at controlling pests like insects.– Simon O’Hanlon
They’re also crucial to the existence of other species and the overall health of our ecosystems, and the impact of their potential extinction is still unknown.
“We really don’t know what the knock-on effect of this kind of worldwide loss of amphibian biodiversity is going to be,” said O’Hanlon. “Amphibians are a major source of food for reptiles and birds, and they’re also very good at controlling pests like insects. So when we lose that many frogs, and species are driven to extinction, we don’t really have a good handle yet on what the potential effects on our ecosystems could be.”
Global pet trade linked to spread of the deadly fungus
The fungus was almost certainly imported because of the global trade in frogs for pets and food. And that’s likely still true today. This research can’t trace the first incidence of the spread of the fungus out of Asia, but frogs are often transported across oceans as part of the pet trade.
Researchers are hoping to gain a recognition that regulations on the trade of amphibians (and all animals) are necessary and essential to help control the movement of pets between continents and the biota that lives on the animals traded for domestic use.