Captive breeding introduced infectious disease to Mallorcan amphibians

September 22, 2008

A potentially deadly fungus that can kill frogs and toads was inadvertently introduced into Mallorca by a captive breeding program that was reintroducing a rare species of toad into the wild, according to a new study published in the September 23rd issue of the journal Current Biology.

The study, by researchers from Imperial College London and international colleagues, reveals that captive Mallorcan midwife toads released into the wild in 1991 were infected with the chytrid fungus Batrachochytrium dendrobatidis (Bd). Measures to screen the health of the toads did not pick up the fungus, because at the time it was not known to science.

The chytrid fungus, which lives in the water and on the skin of host amphibians such as frogs, toads, salamanders and newts, has been known to cause amphibian population extinctions in Europe. Globally, the disease has been found in over 87 countries and has driven rapid amphibian declines in areas including Australia and Central America, pushing some species to extinction. Bd is currently rare in the UK, having only been detected in three locations.

The new study suggests that an endangered species of frog from South Africa, Xenopus gilli, which was housed in the same room as the Mallorcan midwife toads, was responsible for spreading the infection to them.

The captive breeding and reintroduction program for the Mallorcan midwife toad has been highly successful in increasing the numbers of the rare toad on the island. Over half of all the current populations on Mallorca are derived from reintroductions.

Although the chytrid fungus can be deadly, toads appear to be doing well in three out of the four populations in Mallorca infected with the chytrid fungus. This finding suggests that there are unidentified factors that are preventing the extinction of these populations. The situation is being closely monitored by the Mallorcan conservation authorities.

Global efforts to save amphibians from extinction hinge on species being taken into captivity and bred until they can be reintroduced to the wild. The researchers behind the new study say their findings reveal the risks of reintroducing species into the wild even when health screening is carried out, and highlight the need to ensure that species bred in captivity do not become infected with pathogens from other species.

As soon as Bd was discovered in the late 1990s, screening for the disease was incorporated into amphibian conservation plans. Zoos are now moving towards breeding threatened frogs in strictly quarantined, biosecure facilities in an effort to prevent the disease spreading in captivity.

The chytrid fungus has also been added to a list of diseases that need to be quarantined compiled by the World Organization for Animal Health. It is hoped that these quarantine measures will help those involved in conservation efforts to stop Bd from spreading further, by controlling the international trade in infected animals.

Dr. Mat Fisher, one of the authors of the study from the Department of Infectious Disease Epidemiology at Imperial College London, said: "Our study has shown that species reintroduction programs can have unpredicted and unintended effects. However in this case we believe that the toads are going to survive the infection. The global conservation community is united in its goal of saving species from the effects of Bd, and we now have international legislation which should prevent this disease being accidentally introduced into the wild."

The researchers reached their conclusions after comparing the specific genotype of Bd from infected wild toads from across Mallorca, and infected toads from mainland Spain, the UK and the rest of the world. They found that the disease in all Mallorcan toads was of the same genotype, and that this was a different genotype from those on mainland Europe and elsewhere.

Bd infects amphibians' skin and is thought to interfere with their ability to absorb water. Over 257 amphibian species are known to be affected by Bd. Some species are very susceptible and die quickly while others, which are more resistant, are carriers of the pathogen.

Source: Cell Press

Explore further: Research could lead to protective probiotics for frogs

Related Stories

Research could lead to protective probiotics for frogs

July 30, 2015

In research that could lead to protective probiotics to fight the "chytrid" fungus that has been decimating amphibian populations worldwide, Jenifer Walke, PhD, a postdoctoral researcher at Virginia Tech University, Blacksburg, ...

New insight into lethal fungus infection in wildlife

May 21, 2015

The introduction of a lethal fungus infection that could threaten the UK's amphibian populations has not been caused by exposure to infected colonies of African clawed frogs, according to new research from the Universities ...

Genetic variation is a necessity

April 28, 2015

The Earth is constantly changing. For new species to be able to adapt and cope with the changes, there must be sufficient genetic diversity, or genetic variation, in the population. But what type of diversity is required ...

Evolution makes invading species spread even faster

April 22, 2015

Today, invasive animals and plants spread all around the globe. Predicting the dynamics of these invasions is of great ecological and socioeconomical interest. Yet studying them is fundamentally challenging because of the ...

Recommended for you

For 2-D boron, it's all about that base

September 2, 2015

Rice University scientists have theoretically determined that the properties of atom-thick sheets of boron depend on where those atoms land.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.