Frogs Are Experiencing the Greatest Disease Threat to Biodiversity Ever

By Isa Arellano

It’s no surprise that climate change and the destruction of ecosystems have caused severe threats to many animal species populations around the world. For most people, these factors are the first thing they think of as the reasons behind rapidly declining populations in animal species across the globe. 

What you may not know is that for amphibian species, there is a lesser known third threat to their numbers: a devastating fungal disease known as chytridiomycosis. 

What is chytridiomycosis? 

Chytridiomycosis is a disease that infects the skin of amphibians, such as frogs and salamanders, where the fungus produces zoospores that spread into the surrounding environment. These zoospores can remain alive in water for weeks and infect other amphibians, resulting in widespread outbreaks in entire ecosystems. [1] 

It is caused by Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal), which are fungi thought to have originated in Asia near the Korean peninsula and then spread around the world via human trade and travel. The fungi can now be found in every continent except Antarctica and is estimated to affect around 1,300 amphibian species, 501 of which have declines attributed to chytridiomycosis. The disease is particularly harmful to frogs. [1,3] In its native areas, Bd and Bsal can still be found on frogs and salamanders but because these populations have evolved alongside the fungi, these species of amphibians do not develop the disease. The introduction of these Bd and Bsal to new amphibian populations in other regions of the world that did not have any natural resistances turned a minor environmental hazard into a full-fledged pandemic. [2] 

What are the effects on amphibians? 

The skin is an important organ for amphibians, providing not only a protective barrier for the animals but also functions as an absorbent layer for breathing and drinking. [2] Frogs infected with chytridiomycosis experience impairments with oxygen exchange, thermoregulation, nutrient intake, and hydration. [1] It can also irritate the skin and cause shedding and lesions. These lesions allow for harmful bacteria to penetrate the animals’ internal organs, resulting in fatal septicaemia. Amphibians may also experience cardiac arrest due to potassium imbalances caused by ion transport facilitated by skin. [2] 

The severity and widespread nature of chytridiomycosis have left the amphibian populations of certain areas particularly vulnerable. In the early 2000s, over 40% of “the amphibian community collapsed” in tropical highland areas such as Panama. [2] It has been the cause of hundreds of extinction in dozens, if not hundreds, of amphibian species around the world. The Cornell Wildlife Lab even goes so far as to say that chytridiomycosis has caused the “most significant losses of biodiversity from disease in recorded history.” [1]  

But there may be hope for amphibians. 

Although the disease is having catastrophic effects on amphibian populations and their biodiversity, recent research by scientists at Queen’s University Belfast have found that for amphibians in the tropical regions that were hit the hardest signs of stabilization have occurred, with some species potentially having developed resistance or tolerance to chytridiomycosis. One of the research leads, Luke Goodyear, stated that “the peak of devastation might be behind us” in those regions. [4] 

However, the panzootic is still at large.  

Despite the hopeful indicators of recovery to chytridiomycosis in regions most affected by the disease, scientists have also noted that in colder areas like Europe, amphibian populations are continuing to decline as a result of the fungal infections. In fact, the QUB group’s research paper is the “first research to show the increasing impact on these amphibian species at this scale.” Dr. Pincheira-Donoso theorises that this may be because the seasons in colder climates coupled with the low population density of amphibians in those regions have naturally slowed the spread of chytridiomycosis, resulting in a more gradual impact and thus a slower evolution of resistance to Bd and Bsal. 

As scientists continue to research chytridiomycosis and its effects on amphibians, it becomes increasingly important to be aware of how human activity impacts the environment and encourage conservation action before things worsen for our slimy friends. 

References 

[1] “Chytridiomycosis | Cornell Wildlife Health Lab.” 2024. Cornell Wildlife Health Lab. 2024. https://cwhl.vet.cornell.edu/resource/chytridiomycosis. 

[2] “Chytridiomycosis Guide: What It Is and Why It’s Endangering Amphibians.” n.d Discover Wildlife. https://www.discoverwildlife.com/animal-facts/amphibians/facts-about-chytridiomycosis-disease. 

[3] White, Lewis. 2019. “Chytrid Fungus Threatens Even More Amphibians than Previously Realised – Discover Wildlife.” Discover Wildlife. April 2, 2019. https://www.discoverwildlife.com/news/chytrid-fungus-amphibian-declines-extinction. 

[4] “Lethal Pandemic Disease Slowing down the Extinction of Amphibians in Tropical Climates, Study Shows.” Qub.ac.uk . January 23, 2026. https://www.qub.ac.uk/schools/SchoolofBiologicalSciences/News/Lethalpandemicdiseaseslowingdowntheextinctionofamphibiansintropicalclimatesstudyshows.html.