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Where Have the Frogs Gone?





Written by: Aiai Calmer ‘26

Editor: Jasmine Shun ‘24


In the leafy shadows of our planet’s forests, a silent epidemic has been unfolding, one that has managed to escape public attention but has still completely rocked the field of ecology and conservation biology. It hasn’t affected humans or any other mammal, but rather an animal you may pass by every summer night that sings in a harmony of croaks and chirps—frogs.


First identified in the 1990s, Chytridiomycosis is caused by two kinds of chytrid fungi, known as Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) [1]. By 2016, this fungus had been documented in over 60 countries spanning six continents and was named by the International Union for Conservation of Nature (IUCN) as a significant factor in the endangerment of 41% of frog species globally [2]. By 2019, the first global tally of chytridiomycosis found that chytridiomycosis had caused a major decline, if not complete extinction, in at least 501 frog and salamander species [3].


Chytridiomycosis attacks the amphibians’ skin, an organ responsible for their respiration and hydration. Dysregulation of this vital organ can lead to heart failure. Initially, conservation efforts focused on captive breeding programs and habitat management to mitigate the impact of the disease. However, these efforts were only able to slow the disease’s progression, not stop it. Bd is waterborne and spreads rapidly by human activity, so the only way to eliminate it is to dry up every Bd hotspot, which isn’t possible from an ecological perspective. Researchers faced a challenging task: finding a treatment or any other sustainable solution for a disease that had already shown devastating effects on local and global ecology in a very short period of time.


In recent years, the search for a cure has taken an innovative turn. Researchers have been exploring the potential of probiotic therapy, a method that leverages beneficial skin bacteria found on some amphibians. These bacteria produce substances that inhibit the chytrid fungus by literally resisting pathogens and further training and improving the amphibian immune system. Research published in the 'Proceedings of the Royal Society in Biological Sciences' in 2016 demonstrated that introducing the Bd-inhibitory probiotic Janthinobacterium lividum to boreal toads significantly improved their survival rates by 40% [4]. However, there are still some major issues attached to this solution: how would scientists inoculate every single amphibian in the world with this probiotic and is it a viable solution for every species of amphibian in every varying environment?


Another promising area of research is the exploration of low-virulence chytrid fungi as a kind of vaccine against deadlier strains of the fungus. In 2020, research published in Nature provided strong evidence for this hypothesis. The team of scientists found that European midwife toads who were exposed to some low-virulence strain of chytrid fungus were protected against BdGPL, global pandemic strains descendent of the Bd chytrid fungus [5]. The idea is similar to vaccinations in humans: doctors inject a passive form of the virus to build immunity against the virus. If the person is exposed to the active, more dangerous form later on, they are better protected and are more capable of fighting the real virus off. It’s important to note for the research at hand that while this strategy worked well for midwife toads, it was not as effective for newts and not effective at all for salamanders. The same question stands for this research: how do we make this solution viable for a wider range of amphibians across the globe?


In addition to these very specific solutions, there are some broader remedies being implemented that may be applicable to more than just one amphibian species. In 2011, Woodhams et al. proposed several environmental disease mitigation strategies including active management of the fungus in potential hosts and habitats [6]. In one particular example, it turns out that certain microcrustacean species may be able to predate Bd zoospores. There’s also the potential to create chemical treatments that limit infectious zoospores in the environment since Bd is “susceptible to drying, salt, and a broad range of antibiotics and chemicals”[7]. All of the methods described in this paper are still in a relatively early stage of development and are mostly conceptual hypotheses but there is consistent research being done working toward implementation.


As we continue into the 21st century, the chorus of frogs in our forests has been quieted, but there is still hope. The ongoing efforts to combat Chytridiomycosis are not just about saving individual species but are part of a larger journey to maintain the ecological balance of our natural world and preserve biodiversity. The international movement of scientists to save the frogs is a beautiful reminder of the relentless human pursuit of solutions to protect our world’s most vulnerable species. 


Works Cited


1. Lips K. Overview of chytrid emergence and impacts on amphibians. Philosophical Transactions of the Royal Society B: Biological Sciences [Internet]. 2016 Dec 5;371. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5095542/


2. Guardian of Ecuador’s diverse - and vanishing - frog species. Nature [Internet]. Available from: https://www.nature.com/articles/d41586-023-00889-2#:~:text=According%20to%20the%20International%20Union,habitat%20destruction%20and%20climate%20change


3. Scheele BC, Pasmans F, Skerratt LF, Berger L, Martel A, Beukema W, et al. Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity. Science. 2019 Mar 29;363(6434):1459–63. 


4. Kueneman J, Woodhams D, Harris R, Archer H, Knight R, McKenzie V. Probiotic treatment restores protection against lethal fungal infection lost during amphibian captivity. Proceedings of the Royal Society B: Biological Sciences. 283(1839). 


5. Greener MS, Verbrugghe E, Kelly M, Blooi M, Beukema W, Canessa S, et al. Presence of low virulence chytrid fungi could protect European amphibians from more deadly strains. Nature Communications. 2020 Oct 26;11(1):5393.

6. Woodhams DC, Bosch J, Briggs CJ, Cashins S, Davis LR, Lauer A, et al. Mitigating amphibian disease: strategies to maintain wild populations and control chytridiomycosis. Frontiers in Zoology. 2011 Apr 18;8(1):8. 


7. Ibid; Johnson M, Berger L, Philips L, Speare R. Fungicidal effects of chemical disinfectants, UV light, desiccation and heat on the amphibian chytrid Batrachochytrium dendrobatidis. Diseases of Aquatic Organisms [Internet]. 2003 Dec 29 29;57(3):255-60.


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