What is chytridiomycosis?

Chytridiomycosis is a lethal disease of amphibians caused by the aquatic chytrid fungal pathogen Batrachochytrium dendrobatidis (a.k.a. “chytrid fungus” or “Bd”). This disease is the worst case of disease-caused vertebrate biodiversity decline in recorded history.

            Where has this pathogen been found?

World Distribution of the Chytrid fungus (source).

Figure. Orange points are published accounts, white points are unpublished (M. Fisher, www.spatialepidemiology.net/Bd ) 

How does the chytrid fungus kill amphibians?

There is still considerable debate on this topic, but in most cases, infection leads to hyperkeratosis of the skin ("thickening" of the skin, sometimes up to 40 times thicker than normal). These two photos show a cross sections of healthy frog skin (left) and infected frog skin (right).
Disruption of the skin's normal functions leads to multiple complications, usually leading to death.  In amphibians the skin is one of the most important organs; many species do not have lungs and breathe entirely through their skin.

The effects can be devastating! Just below the world map are photos of dead frogs and a very sick frog (Southern Mountain Yellow-legged Frogs) at my study site in Kings Canyon National Park, California.

What is the life cycle of the chytrid fungus? 

            see Biology of the phylum chytridiomycota

Can the chytrid fungus be contained?

            see How to prevent the spread of chytridiomycosis (PDF)  

How is a chytrid infection detected?

            We use a non-destructive technique (skin swabs) that allows us to sample live amphibians without harming them (see a video demonstration).  We use a real-time PCR assay to test whether the animals are infected with the chytrid pathogen (Batrachochytrium dendrobatidis). 

            What is real-time PCR?

            How does real-time PCR allow estimation of infection load?

We use a PCR assay that enables us to measure the presence and quantity of Bd zoospores collected from amphibian skin swabs. The technique compares the amount of Bd DNA in the sample to a universal set of standards (know quantities of Bd DNA). Below you can see output from one of our sample runs. All of the samples that cross the green horizontal line are positive for Bd.  Those that cross the line earlier (i.e. at a lower cycle number) have more Bd DNA, those that cross the line later have less Bd DNA.            

Other links for chytridiomycosis:

            AmphibiaWeb page:  chytridiomycosis

            Taxonomy:  (chytrid fungi online)

            Tree of Life description of chytridiomycete fungi

            Scientific literature on chytridiomycosis



chytrid fungus

Vredenburg Amphibian Research Group









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David Liittschwager