Chytridiomycosis

Croaking science is a new way for student volunteers and scientist to explore what’s occurring in the world of Science. Croaking Science looks at science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicates this in layman’s language to a wider audience. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists. We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.

Croaking Science reporter Rhiannon Laubach looks at the history of chytridiomycosis and its impacts on the Fire Salamanders in Europe

The current worldwide loss of amphibians has reached crisis level. Some 40% of amphibian species in parts of Central America are at risk of extinction and there are also large scale losses in Europe, North America and Australia.  The main cause for this is an infectious disease known as ‘fungal chytridiomycosis’, chytrid or Bd for short.  Click here for a map showing global chytrid distribution.

Chytrid is a fungus that infects vertebrates with spores that grow in the top keratin layers of the infected host’s skin. Symptoms of chytridiomycosis in amphibians include lethargy, lost righting reflex and an abnormal posture. The amphibian’s skin can be ulcerated and slough off in an uncharacteristic way and haemorrhages can occur in the eyes, muscles and skin. The disease is fatal to almost all amphibians (Martel & al 2014).

The earliest evidence for chytrid has been found in a museum collection of African clawed frogs that were collected in Africa in 1938. The exportation of these frogs around the world, for human pregnancy testing and other research, is the likely vector for the spread of the fungus. The first case of chytrid outside of Africa was recorded in North America in 1961 (Laurence 2008). Its spread is made easier because particular species such as the African clawed frog can be affected by the fungus asymptomatically meaning that they do not show any symptoms of the disease.

It used to be thought that there was only one species – Batrachochytrium dendrobatidis – with several different strains that infected all amphibians. However, Dutch scientists studying high mortality rates in the fire salamander (Salamandra salamandra) have discovered a new species of chytrid known as Batrachochytrium salamandrivorans (meaning salamander skin-eating fungus).

In the Netherlands, the fire salamander population has decreased so dramatically that it has brought it to ‘the edge of extinction’ in this country.  From 2010 to 2013, the salamander population decreased by 96%.  When researchers analysed the dead salamanders to see what was causing the fatalities, they were able to isolate the new species of chytrid.

Salamanders that are affected by this disease, usually die after suffering from anorexia, apathy and ataxia.  The infected animals have deep ulcers and shallow erosions all over their bodies which are then colonised by bacteria.

It was necessary for the researchers to find out if the new chytrid species was definitely the cause of the salamandrid mortality.  These experiments involved infecting salamanders with chytrid.  This research seems quite cruel but was necessary as the researchers needed to see how the fungus infected the salamanders.

Summary of experiment:

• Healthy salamanders were inoculated with spores of the chytrid fungus, they all died by day 18.  Two healthy salamanders where introduced into the tank, these salamanders where fatally infected.
• The common midwife toad (Alytes obstetricans) is easily infected by Batrachochytrium dendrobatidis, toads have been experimentally infected with Batrachochytrium salamandrivorans.  The toads where not colonised bythe new fungus species suggesting that it does not affect, or easily affect, other amphibian species such as frogs or toads (Martel & al 2014).

Amphibians are a diverse and charismatic class of species.  On a worldwide scale they are increasingly threatened by a wide range of threats such as habitat loss and climate change. Chyrtrid may be what pushes many vulnerable species to extinction.  As a result of their plight 2014 has been designated as Year of the Salamander by the Amphibian Survival Alliance and their partners.

What you can do

This can be a depressing topic but there are things that we can all do to help protect amphibian populations:

• Find out more, click here to find out more about Chytrid
• Try to make your gardens as amphibian friendly as possible
• Record and monitor the health of amphibian populations.  You can report diseased or dead animals found in your garden to the Garden Wildlife Health project.  This will help researchers build a better picture of the state of our garden wildlife and understand the threats that it faces
• Support amphibian friendly charities.  There are lots of ways you can support Froglife you can: become a Froglife Friend, donate, shop online with Give as you Live (at no extra cost to you) or volunteer

References

Lawerence, D. (2008). Batrachochytrium dendrobatidis, Chytrid disease. Available: http://depts.washington.edu/oldenlab/wordpress/wp-content/uploads/2013/02/Batrachochytrium-dendrobatidis_Lawrence.pdf. Last accessed 2nd April 2014.

Martel,A., Spitzen-van der Sluijs, Blooi, M., Bert, W., Ducatelle, R., Fisher, M., Woeltjes, Bosman,W., Chiers, K.,Bossuyt,F., Pasmans, F. (2014). Batrachochytrium salamandrivon sp nov. causes lethal chytridiomycosis in amphibians. Available: www.pnas.org/cgi/doi/10.1073/pnas.1307356110. Last accessed 31 March 2014.