Amphibian chytridiomycosis

For more than 20 years, ZSL has been at the forefront of research on amphibian chytridiomycosis, a disease which has devastated amphibian populations globally. 

Summary of the research

The global decline of amphibians is one of the most important biodiversity crises facing us today. Amphibian declines have many causes, but until the late 20th century infectious disease had not been identified as a factor. In the mid-1990s, however, an international team of scientists led by Professor Andrew Cunningham, a researcher from ZSL’s Institute of Zoology (IoZ), identified a novel infectious agent, Batrachochytrium dendrobatidis (Bd), a chytrid fungus that produces the amphibian disease chytridiomycosis, and demonstrated that this was a major cause of amphibian mortality and declines on at least two continents.

At this time, Prof. Cunningham was Chair of the Pathology & Disease Working Group of the IUCN’s Declining Amphibian Population Task Force, which enabled him to bring together amphibian decline researchers and pathologists across the world and which resulted in this discovery; an effort described as "an exemplary example of international scientific collaboration" (Nature 394, 418-419). Prof. Cunningham and the team were each awarded a medal by the CSIRO in Australia for this work. 

Subsequently, IoZ’s scientists have spent close to two decades working on this disease, including collaborating with researchers from dozens of countries to understand the current status and underlying drivers of the distribution, spread and impacts of Bd. In particular, we have described infection and lethal impacts in dozens of amphibian species across Europe, the Caribbean, South America, Africa and Asia. 

Mountain chicken frog

As the amphibian decline crisis deepened, a ZSL amphibian working group was established to bring staff together from across the organisation to maximise our efforts to combat amphibian declines through research, in-country conservation and capacity building and conservation breeding in ZSL London Zoo. Some of our zoo-bred animals, housed under biosecure conditions, have been released back into the wild with careful post-release monitoring to learn from successes and failures alike. In all these areas we work closely with other institutions, including universities, governments and other conservation non-governmental organisations.

Our work and other studies have shown that the mortality caused by chytridiomycosis can cause catastrophic and persistent amphibian population declines that may, in extreme cases, result in species extinctions. Collectively, this has identified environmental conditions and amphibian taxonomic groups that are at greater risk of disease emergence and decline due to chytridiomycosis. Using state-of-the-art genome sequencing technology, we have shown how the recent evolution of Bd produced a novel, hypervirulent and now globally-distributed form of the pathogen that is predominantly responsible for amphibian mortality and declines worldwide.

We continue to identify new variants of Bd using next-generation sequencing technologies and we are currently investigating how competition amongst genetic variants may be behind the evolution of hypervirulence. In addition, ZSL staff were involved in the recent discovery of a completely new species of chytrid fungus that is devastating fire salamander populations in Western Europe and we have been at the forefront of working with the British government to try to mitigate any impacts this new disease might have on amphibians in the UK.

We are constantly translating our world-class research on chytridiomycosis into conservation strategies that combat this threat to amphibians. IoZ scientists have shown how introduced and non-native species may commonly harbour infections and how movement of amphibians for trade and even conservation purposes can expand the range of Bd and other pathogens.

We work with national and international entities to develop strategies that our research indicates will reduce the risk of infection being spread by the amphibian trade and reduce the risk of spill-over from captive to wild populations. We are at the forefront of amphibian welfare, developing methods for treating infection in both captive and wild populations. Our latest work takes our welfare research into the wildlife conservation setting: we are the first to publish evidence that infection can be cleared from wild amphibian populations.

• Find out how ZSL is working to protect mountain chicken frogs
   
• ZSL hosted a scientific event in April 2017 on conserving the mountain chicken frog: the impact of chytridiomycosis under scrutiny. Listen to the podcast