Frog Fungi - A Global Problem Affecting Amphibians

Chris -   Amphibian species around the world are subject to an increasing threat in the form of a fungus.  Over 200 amphibian species are thought to have become extinct and the problem isn't just restricted to frogs, toads and newts.  During the 19th century, for instance, a fungal infection caused the potato famine in Ireland and, according to new research, it could affect food security today.

Planet Earth podcast presenter Sue Nelson went to London Zoo's reptile house - of Harry Potter fame - to meet up with Trent Garner, from the Institute of Zoology, and Matthew Fisher from the department of infectious disease epidemiology at Imperial College London.

She began by asking Matthew why we haven't we heard more about fungal infections affecting biodiversity...

Matthew -   Fungal infections haven't really been a problem until the last two decades and what we've noticed is that there are far more infections now than there used to be.  I mean we know about fungi driving frogs extinct but there have also been very aggressive emergences in bat populations in North America, bat white-nose syndrome, and we're also seeing dramatic emergences in forests, so we all know about Dutch Elm disease but also in crops too.  There are new virulent forms of fungal lineages which can devastate entire crops, so UG99 has a demonstrated potential to wipe out a quarter of the world's wheat supply.  So, we've been thinking very hard about why this is occurring and what these trends that we're observing actually mean.

Sue -   Let's look, in particular, at how a fungus affects one particular species and that's frogs. Trent, how bad have frog populations been affected?

Trent -   In some parts of the world they are thinking that species have actually gone extinct due to this fungus and that's a rather unusual thing, to have a parasite drive its host to extinction.  Not only has this happened in one part of the world but it has actually happened on multiple continents and that's the thing that's so worrying that such an unusual occurrence can actually be replicated on a global scale.  Of course that's not just species extinctions that are happening, we're seeing catastrophic population declines where the remnant populations are so small that they could go extinct at the blink of an eye for any reason, because there's just not enough numbers there to maintain the population and again this is occurring at a global scale.

Sue -   I think it's time, listening to those helicopters, to actually go inside the reptile house, get out of the noise here, and perhaps go and see some of the frogs that have been affected...

...It's still noisy but it's a popular time, lots of school children and familiar glass fronted cases containing snakes and lizards, geckos on my left there, African Bull Frog and a Blue Poisoned Dart Frog - oh, that is beautiful, that is a vivid blue isn't it?

Trent -   They are beautiful aren't they?  They come from a family of frogs that has been heavily affected by the fungus in Latin America.  Some of the species within the family are presumed extinct due to the emerging infectious disease.

Sue -   Is the fungus that affects these frogs the same, Matt, that affects all frogs around the world or are there different strains?

Matthew -   No, there's one single strain that's emerged and we've dated that to the mid 1970s or perhaps a little bit earlier than that and that seems to have emerged pretty much simultaneously in five continents.

Trent -   If we go over here there's actually a salamander species called the axolotl and it's a member of the family of ambystomatid salamanders and, while we don't have any evidence of this species actually being affected by the disease, they certainly are infected with the fungus, and it's a critically endangered species.

Sue -   Matthew mentioned about the spread over five continents, what has caused the fungus to be spread in that way?

Trent -   I think that's a really good question and I think we're still developing the evidence base to actually answer that question. Certainly, a lot of people invoke amphibian trade as being responsible for the spread and we do have some evidence that amphibian trade has been responsible for some spread events.  Exactly how it's been responsible for spread overall is yet to be determined.

Sue -   When you have a fungus that can affect and potentially devastate crops of wheat or rice that's extremely worrying.  What can be done about this?

Matthew -   We would argue that much stronger international bio-security is necessary. We see the doors to our country as absolutely wide open for the trade of animals and plants in the nursery trade or in the pet trade and these hosts have the demonstrated potential to carry new infections into countries and we're witnessing the effect of that, the manifested potential of these pathogens.  So we need to quarantine more and we need to give the international organisations which control trade in bioactive material more muscle.

Sue -   Do you think it's too late, Trent?

Trent -   No. I agree with Matt that we need to tighten up regulations and tighten up enforcement to reduce the risk of disease being transported around. But even if disease occurs in an area, even if disease does emerge in an area, I do think that steps can be taken to reduce forcing of infection and potentially reduce the effects of the parasite without necessarily eliminating the parasite.

Chris -   Trent Garner from the Institute of Zoology and Matthew Fisher from the department of infectious disease epidemiology at Imperial College London.  And a longer version of that report from Sue Nelson can be heard in the latest Planet Earth podcast. You can download it from our website or via Planet Earth Online.