Chytrid: What is it and why does it suck?

What is it?

Chytridiomycosis (chytrid for short), also known as Batrachochytrium dendrobatidis, Bd, or frog plague, has many names and an awful track record of global amphibian destruction. According to the Chytridiomycosis fact sheet provided by the Australian Department of Sustainability, Environment, Water, Populations and Communities (2013), amphibian chytrid is a highly infectious disease that has been causing frog and salamander declines–some populations have seen a 100% mortality rate–since at least the 1970s. Other types of chytrid fungi are usually found underwater on dead plants or animals but Batrachochytrium dendrobatidis is a particularly nasty variety that feeds on live prey (“Amphibian Chytrid Fungus” 2018). This fungus isn’t like athlete’s foot or ringworm; it’s deadly. To understand why this is such a huge deal, we need a crash course in amphibian physiology.

Amphibians and their skin-lungs:

Two lined salamander (Eurycea bislineata). It is a member of the lungless salamander family (Plethodontidae)

Most amphibians depend on water because their skin acts like a giant external lung and needs to be kept moist. Frogs and salamanders have highly vascularized semi-permeable skin that allows for partial or total gas exchange. Some salamander species–and at least one frog species–have forgone lungs altogether and breathe solely through their skin, a process called cutaneous respiration (Vitt & Caldwell 2013).

Note: Keep this is mind when handling amphibians. You wouldn’t go nonchalantly poking someone’s exposed lung, so be mindful of the fact that improper capture of amphibians can damage their ability to breathe. Furthermore, salt and chemicals from your skin can pass through the amphibian’s skin and into their bloodstream. Avoid handling when you can, and don’t hold an amphibian longer than is necessary. Make sure your hands are clean and moist or that there is a barrier between your hands and the animal so your amphibian friend can survive the encounter and walk away happy and healthy!!!

Why does chytrid suck?

The chytrid fungus is dangerous to amphibians because it damages the skin and blocks both water and gas exchange. Over time the infected animal becomes lethargic, dehydrated, and unable to avoid predators. In many cases (though some species are naturally resistant to the effects of the fungus) the chytrid infection is fatal (“Amphibian Chytrid Fungus” 2018). Along with being virulent, amphibian chytrid fungus is also highly contagious AND spreads through water and soil through spores (“Chytridiomycosis” 2013). It occurs on every continent that has amphibians but no one knows exactly where it came from (“Amphibian Chytrid Fungus” 2018). It can be cured individually with antifungal medication but because it affects amphibians on such a large scale it is impossible to contain and treat infected populations. In Australia alone, amphibian chytrid led to the extinction of at least four species of frogs and has drastically reduced the populations of at least ten others (“Chytridiomycosis” 2013). Globally, amphibians are dying off at an unprecedented rate and without intervention it could lead to the mass extinction of amphibians worldwide (Rosenblum, Voyles, Poorten & Stajich 2010).

What can we do about it?

Even though we don’t know where the fungus comes from, we do know how it’s spread. Make sure to clean off boots or waders when moving from place to place, avoid releasing amphibians in different bodies of water than where they were found, and don’t cross contaminate your catch containers or nets. Also, citizens like you and me can help scientists assess the biodiversity worldwide by…..

JOINING THE GLOBAL AMPHIBIAN BIOBLITZ!

The best way to figure out how chytrid–amid other factors–affects worldwide amphibian populations is by seeing what’s out there. By logging amphibian observations, photos and locations, everyday citizens can help scientists and conservationists get an idea of the bigger picture and move forward with conservation efforts. Sign up with inaturalist, get out into the muck and look for amphibians!!

Invasive Cuban treefrog (Osteopilus septentrionalis) found in Melbourne, Florida

Citations:

Amphibian Chytrid Fungus. (2018). Retrieved April 2, 2019, from https://www.nps.gov/pinn/learn/nature/chytrid.htm

Chytridiomycosis (Amphibian chytrid fungus disease). (2013). Retrieved April 2, 2019, from https://www.environment.gov.au/biodiversity/invasive-species/publications/factsheet-chytridiomycosis-amphibian-chytrid-fungus-disease

Rosenblum, E. B., Voyles, J., Poorten, T. J., & Stajich, J. E. (2010, January 29). The deadly chytrid fungus: A story of an emerging pathogen. Retrieved April 2, 2019, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2813266/

Vitt, L. J., & Caldwell, J. P. (2013). Cutaneous Respiration. Retrieved April 2, 2019, from https://www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/cutaneous-respiration

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