Since its discovery almost two decades ago, the disease chytridiomycosis has devastated amphibian populations globally. Caused by a type of fungi, the deadly infection, also known simply as chytrid, has driven multiple species of amphibian to the edge of, and some into, extinction. Whilst it’s possible to cure the disease in the lab, the fungus thrives in the same damp, humid environments that are so loved by their amphibian hosts, making it difficult to eliminate in nature.
But in a world first, by treating tadpoles with antifungals and the environment with a chemical disinfectant, researchers have announced that they have quite incredibly managed to cure the disease in two wild populations of frogs. The amphibians in question are Majorcan midwife toads, of which around 1,000 are thought to remain on the Mediterranean island. The toads have been previously saved from extinction through captive breeding programs.
A Majorcan midwife toad has succumbed to chytridiomycosis. Jaime Bosch/MNCN
“By combining the antifungal treatments with this environmental disinfection, we have so far managed to clear the infection for three years now in one of the ponds,” explained Dr. Trenton Garner, who co-authored the paper published in Biology Letters, to IFLScience. “In one other pond, we also managed to clear it successfully, but another has retained the infection. So basically, we’re one pond shy of clearing chytrid from infecting this species on the entire island.” Dr. Garner is, however, confident that they will be able to clear the last pond, and “kick it right off the island.”
The disease is caused by the highly infectious fungi Batrachochytrium dendrobatidis (Bd) and is thought to have possibly originated in Africa, but has now spread to almost every continent. Not all frogs are susceptible to the disease, but in those that are, it causes the amphibians’ highly porous skin to thicken and prevents water and other important salts from being absorbed by the amphibians. This disrupts the balance of electrolytes in the body, eventually causing the frog's heart to stop beating.
One of the few ponds in which the Majorcan midwife toad lives. Jaime Bosch/MNCN
Amphibians can be cured of the disease in the lab by bathing them in antifungal treatments. But when Dr. Garner and his colleagues from the Zoological Society of London, the Museum of Natural History in Spain, and Imperial College London then reintroduced cured tadpoles back into the island ponds, they found that they were somehow reacquiring the infection. “We decided we had to do something else, and we took the step up and used the environmental disinfectant,” said Dr. Garner.
While it might sound dramatic, the team purposely chose a disinfectant that they presumed would have minimal impacts. So far during the past three years, things seem to be going well, according to Dr. Garner. “Certainly from the amphibian side of things we’re not seeing any negative impact of [development to adulthood] in the sites we’ve applied them, so they’re still laying eggs and hatching out tadpoles,” he explains.
Dr. Garner finishes by noting that while this news is incredibly exciting and definitely a ray of hope, it is simply another tool in the arsenal needed to help protect amphibians and prevent them from slipping into extinction. He warns that while a lot of focus has gone into chytridiomycosis, there are a whole host of other pathogens that are affecting amphibians, and we need to come up with other tools to fight these.