Batrachochytrium Dendrobatidis

Batrachochytrium Dendrobatidis is a deadly disease that has decimated populations of frogs the world over.  It is found on the skin of frogs and was first discovered by an English Biologist called Lee Berger in Australia in 1988.  She was asked to look into why there had been a huge and rapid decline in amphibian numbers in Australia over a fairly short period of time, like two decades.  She was asked to carry out this work by as there was a belief that a fungal infection could not really be responsible for wiping out an entire species.  During her work Berger discovered a fungus called chytrid fungus (formally Chytridiomycota).  Chytrids are part of a group known as zoosporic organisms that are within the fungi kingdom. This chytrid fungus interferes in a big way with the skin of a frog and causes it to be unable to absorb water and electrolytes and ultimately and sadly leads to the death of the frog affected.

Batrachochytrium dendrobatidis spreads through water, dispersing zoospores into the water, which then move by way of flagella, to reach a new host and attach and enter it through the skin.  This means that via a sporangia (which is like an enclosure where spores can be formed)  new zoospores are produced.   The disease spreads when the new zoospores reinfect the original host.  There are signs that can indicate when an amphibian has been infected and it can include things such as reddening of the ventral skin (so, on the front of the frog, for example the belly),  convulsions and sloughed skin on the body.  The frog may also sit in a funny position with its legs far away from its body, and it may fail to seek shelter, become lethargic and be unable to flee from danger.  It can also sometimes display little skin tags and ulcers on its skin.

There have been populations of frogs wiped out in Central, North and South America, as well as eastern Australia, east Africa, and Dominica.  At the moment, sadly there is not really any known effective way of controlling the spread of this fungus and Batrachochytrium dendrobatidis is likely to spread further as time goes on.

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It is not known if chytridiomycosis is some form of older pathogen that has increased in virulence recently, or whether it is a new pathogen that has hit the frog population.  However, the first documented case of Batrachochytrium recorded was way, way back in 1863 and was found in the extremely rare Titicaca frog which lives in Lake Titicaca which is one of the world’s highest large freshwater lakes situated between Peru and Bolivia. 

 

Lake Titicaca

Climate change is probably going to be encouraging the spread of the fungus, as temperatures rise in forest environments, and the evaporation rate increases cloud formation.  This cloud formation will consequently reduce the daytime temperature, but it also will increase the night time temperature as the clouds prevent any heat accumulated during the day, from escaping up and away into the sky, which could well be resulting in perfect temperatures for the growth and reproduction of the chytrid fungus.  The fungus is not able to survive for long in temperatures above 30°C and if the cloud formation was not there during the day, the heat would probably kill it off.

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