The frustrating case of chytridiomycosis researchers

I began my research career working with amphibians, in particular the Eleutherodactylus frogs of Puerto Rico. One of the reasons I distanced myself from the whole area, other than just finding new interests, was largely a feeling of frustration over the lazy science that was taking place and occupying all the spaces, and funding, in amphibian declines: chytridiomycosis. This disease is caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd) and has been associated with population declines and extinctions in several places in the world since the 90s. The problem is that big conservation projects are being put in place while basic questions still get no attention.

Although Koch postulates were met (the disease is caused by the Bd and it can kill individuals after infection), there is more than plenty of evidence that some species and populations can survive or are not affected by Bd. Why most researchers in the area still talk about presence as reason enough for a threat to all the species in an area?

I attended the 2013 ESA meeting and one of the presentations was on a model of infection of the disease. The problem was that the model made several assumptions that were obviously wrong, but were not justified. In particular, the presence of the zoospores in the medium was ignored, when it is known that the fungus has to re-infect the individual from the outside. The fungus creates more zoospores in the skin cells, which are expelled to the medium to infect other cells. Cell to cell infection seems to not take place.

Another example of the many problems in this area is the case of the “wave” of infection of Bd that covered Central America. The problem with this wave was that the analysis ignored everything we know about landscape ecology, infectious diseases, and even the Bd fungus biology. This fungus, which travels only as a zoospore in water, supposedly crossed the whole of Central America, across mountains, cities, and vastly different landscapes, at a steady rate. No alternative hypotheses were tested or any known animal or human epidemic was used to justify the wave hypothesis.

In the case of Puerto Rico, Bd has no effect on the most common species, yet some researchers insist on studying it as a threat. Last I heard, the only way they found to infect and kill the frogs was submerging them in a solution with an insanely high density of the fungus, something that will never happen in the field. Again, biology and infectious disease behavior were ignored to sustain the story of a “risk” of Bd.

In the case of the presentation I saw at ESA, I asked if there had been any comparison with infectious disease models, data, or examples – the answer was “no”. How come there is so much money being invested into this problem, yet no one can tell if it behaves like any known disease, in order to learn more from it? How come zoos are going crazy building “amphibian arks” to save species without first confirming that Bd is a threat to the species they are removing from the field?


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