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The chytrid, a pathogenic fungus

Dyeing poison dart frog (Dendrobates azureus). The chytrid fungus (Batrachochytrium dendrobatidis), a pathogen responsible for the decline of population declines in 500 amphibian species and the presumed extinction of 90 others, was first isolated and described from a frog of the family Dendrobatidae (Longcore et al. 1999).
Credit: Biodôme de Montréal
The chytrid, a pathogenic fungus
  • The chytrid, a pathogenic fungus
  • The chytrid, a pathogenic fungus
The chytrid, a pathogenic fungus

As I write these lines, our world is on pause. For several months now, we have attentively followed the wildfire propagation of a viral disease known as COVID-19 around the world. From Asia to home, nobody will contest the role that the massive, growing and tireless international movement of humans has played in the shockingly fast evolution of this pandemic. Yet, simultaneously, but more subtly, the international commerce of animals, plants and  comestible goods is also contributing to the spread of pathogens that threaten a multitude of animal and plant species, adversely affecting ecosystems on which we depend for such ecological services as pollination, food security, carbon fixation and climate control.

An epizootic affecting animals

Amphibian populations already face a number of devastating threats, including habitat loss, climate change and invasive species. However, the final blow to many often arrives abruptly in the form of a fungal pathogen called the chytrid fungus (Batrachochytrium dendrobatidis), believed to originate from Korea. This fungus has been especially lethal to amphibians inhabiting moist tropical areas in Central America and Australia. Upon infecting its highly permeable skin, the chytrid causes a thickening of an amphibian’s skin that interferes with cutaneous respiration, triggering an imbalance of electrolytes that leads to cardiac arrest within a matter of days. Chytridiomycosis is now known as the emerging infectious disease responsible for the greatest loss in biodiversity ever recorded, having lead to the decline of 500 amphibian species and the presumed extinction of 90 others, in only 50 years. Researcher Matthew Fisher, a specialist of fungal pathogens, has described apocalyptic scenes wherein one could walk on a carper of frogs killed by the chytrid fungus. Unfortunately, only 12% of affected species have shown signs of rebounding; and then, only at the local level. Although treatments that successfully heal individuals from infection have been developed, the chytrid can persist in the environment, rendering wider scale treatment of individuals ineffective. Moreover, some amphibian species act as asymptomatic carriers of the fungus, thereby serving as disease reservoirs. It’s in this urgent context necessitating amphibian conservation action that the Montreal Biodome, along with 50 zoological institutions in the United States and Canada, has committed itself to maintaining a genetically sound captive population of Panama golden frogs (Atelopus zeteki), in the hopes that it can one day be released back into its native habitat that is presently contaminated by the chytrid.

A motivation for change

The economic, political and social impacts of COVID-19 prompt motivation to revise our habits and activities, to avoid future pandemics. For decades, researchers like Matthew Fisher have been asking for additional measures to increase biosecurity during international exchanges of animals, plants and goods. Perhaps, in the present context, their voices will be better heard.

The arrival of COVID-19 forced this worldwide pause upon us, and consequently, research and conservation projects aiming to protect amphibians from the chytrid fungus and other important threats are also on hold; just when amphibians need us most! Such projects are mainly supported by zoological institutions, universities, governments and nongovernmental organizations, but these entities have also been adversely affected - financially and otherwise - by the current pandemic. Would you like to lend a hand to the people that help amphibians? Visit such sites as  Save the Frogs, Amphibian Ark, or the Atlas of Amphibians and Reptiles of Quebec to find out what you can do!

Sources:

  • Fisher, MC, Henk, DA, Briggs, CJ, Brownstein, JS, et al. (2012). Emerging fungal threats to animal, plant and ecosystem health. Nature 484: 186-194
  • O'Hanlon, SJ, Rieux, A, Farrer, RA., Rosa, GM., et al. (2018). Recent Asian origin of chytrid fungi causing global amphibian declines. Science, 360 (6389): 621-627
  • Longcore, JE, Pessier, AP, Nichols, DK. (1999). Batrachochytrium dendrobatidis gen. et sp. nov. a chytrid pathogenic to amphibians. Mycologia (91) 2: 219-227
  • Russo, CJM. Russo, Ohmer, MEB, Cramp, RL, Franklin, CE. (2018). A pathogenic skin fungus and sloughing exacerbate cutaneous water loss in amphibians. Journal of Experimental Biology, 221, jeb167445. doi: 10.1242/jeb.167445.
  • Scheele, Pasmans, F, Skerratt, LF, 2019). Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity. Science 363 (6434): 1459-1463.
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