Toads in a hole? Fungal disease threatens UK toad population

New study models potential effects of chytrid fungus

Imperial College London News Release

Under strict embargo for
00.01 GMT
Wednesday 28 November 2007

The UK's toad population could be facing a bleak future because of a deadly fungal disease, according to a new study published today in the journal Proceedings of the Royal Society B.

The deadly chytrid fungus Batrachochytrium dendrobatidis (Bd) is highly effective at causing extinctions among local populations of amphibians and it has already wiped out vast numbers of amphibians in areas including Australia and South America. In the UK, the chytrid is found only in Kent, but researchers fear that in time it may spread across the country.

The fungus lives in the water and on the skin of host amphibians and the new study shows that the length of time that is able to survive on its own in water is key to determining what its impact might be.

One reason suggested for its devastating impact is that it is able to survive in water for long periods of time, allowing it to infect large numbers of amphibians as they pass through. However, the amount of time that the chytrid is able to survive outside the host is not known.

The researchers at Imperial College London and the Institute of Zoology used mathematical models to see the effects of introducing the chytrid into a breeding population of common toads (Bufo bufo), varying the amount of time that it survived outside the host.

The new models showed that if the chytrid was able to live outside the host for a year, the impact on UK toads would be considerable, with severe declines in the numbers of toads and, in some cases, extinction in 10 years within infected areas.

Research has demonstrated that the chytrid is able to live for at least seven weeks outside the host. However, the rapid declines in amphibian numbers elsewhere in the world support the idea that the chytrid may be able to persist for a much longer period of time than has so far been demonstrated in the laboratory.

Dr Mat Fisher, corresponding author of the research from the Department of Infectious Disease Epidemiology at Imperial College, said: "We don't know enough about the chytrid to predict how it is going to behave in the UK, but we start to see dramatic effects if the chytrid lives for longer than 7 weeks outside the host. We strongly suspect that it can live for longer because of the devastating effect it has had elsewhere, and the new models show that this would be very bad news for toads in this country."

The models showed that there was little effect on the UK toad population size if the chytrid was only able to live outside the host for seven weeks.

Bd infects the skins of amphibians such as frogs, toads, salamanders and newts and is thought to interfere with their ability to absorb water. More than 140 species of amphibians are known to be affected by it. Some are very susceptible and die quickly while others, which are more resistant, are carriers of the pathogen. One lucky species, the common British frog (Rana temporaria), appears to be completely resistant to Bd.

-ends-

**Photographs of the common toad are available in 300 dpi***

For further information please contact:

Laura Gallagher
Press Officer
Imperial College London
e-mail: l.gallagher@imperial.ac.uk
Telephone: +44 (0)207 594 6702 or ext. 46702
Out of hours duty Press Officer: +44 (0)7803 886 248

Notes to editors:

1. "Persistence of the emerging pathogen Batrachochytrium dendrobatidis outside the amphibian host greatly increases the probability of host extinction" Proceedings of the Royal Society B, 28 November 2007

Kate M. Mitchell (1)(3), Thomas S. Churcher(1), Trenton W.J. Garner(2), Matthew C. Fisher(1)*

(1) Department of Infectious Disease Epidemiology, Imperial College London
(2) The Institute of Zoology, Zoological Society of London
(3) Current address: Centre for Infectious Diseases, University of Edinburgh

*Corresponding author: matthew.fisher@imperial.ac.uk.

2. Rated as the world's fifth best university in the 2007 Times Higher Education Supplement University Rankings, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 11,500 students and 6,000 staff of the highest international quality.

Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

With 66 Fellows of the Royal Society among our current academic staff and distinguished past members of the College including 14 Nobel Laureates and two Fields Medallists, Imperial's contribution to society has been immense. Inventions and innovations include the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of our research for the benefit of all continues today with current focuses including interdisciplinary collaborations to tackle climate change and mathematical modelling to predict and control the spread of infectious diseases.

The College's 100 years of living science will be celebrated throughout 2007 with a range of events to mark the Centenary of the signing of Imperial's founding charter on 8 July 1907. Website: www.imperial.ac.uk