A potentially deadly fungus that can kill frogs and toads wasinadvertently introduced into Mallorca by a captive breeding programmethat was reintroducing a rare species of toad into the wild, accordingto a new study published today in the journal Current Biology.
The study, by researchers from Imperial College London and internationalcolleagues, reveals that captive Mallorcan midwife toads released intothe wild in 1991 were infected with the chytrid fungus Batrachochytriumdendrobatidis (Bd). Measures to screen the health of the toads did notpick 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 hostamphibians such as frogs, toads, salamanders and newts, has been knownto cause amphibian population extinctions in Europe. Globally, thedisease has been found in over 87 countries and has driven rapidamphibian 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 SouthAfrica, Xenopus gilli, which was housed in the same room as theMallorcan midwife toads, was responsible for spreading the infection tothem.
The captive breeding and reintroduction programme for the Mallorcanmidwife toad has been highly successful in increasing the numbers of therare toad on the island. Over half of all the current populations onMallorca are derived from reintroductions.
Although the chytrid fungus can be deadly, toads appear to be doing wellin three out of the four populations in Mallorca infected with thechytrid fungus. This finding suggests that there are unidentifiedfactors that are preventing these populations from extinction. Thesituation is being closely monitored by the Mallorcan conservationauthorities.
Global efforts to save amphibians from extinction hinge on species beingtaken into captivity and bred until they can be reintroduced to thewild. The researchers behind the new study say their findings reveal therisks of reintroducing species into the wild even when health screeningis carried out, and highlight the need to ensure that species bred incaptivity do not become infected with pathogens from other species.
As soon as Bd was discovered in the late 1990s, screening for thedisease was incorporated into amphibian conservation plans. Zoos are nowmoving towards breeding threatened frogs in strictly quarantined,biosecure facilities in an effort to prevent the disease spreading incaptivity.
The chytrid fungus has also been added to a list of diseases that needto be quarantined compiled by the World Organisation for Animal Health.It is hoped that these quarantine measures will help those involved inconservation efforts to stop Bd from spreading further, by controllingthe international trade in infected animals.
Dr Mat Fisher, one of the authors of the study from the Department ofInfectious Disease Epidemiology at Imperial College London, said: "Ourstudy has shown that species reintroduction programs can haveunpredicted and unintended effects. However in this case we believe thatthe toads are going to survive the infection. The global conservationcommunity is united in its goal of saving species from the effects of Bdand we now have international legislation which should prevent thisdisease being accidentally introduced into the wild."
The researchers reached their conclusions after comparing the specificgenotype of Bd from infected wild toads from across Mallorca, andinfected toads from mainland Spain, the UK and the rest of the world.They found that the disease in all Mallorcan toads was of the samegenotype, and that this was a different genotype from those on mainlandEurope and elsewhere.
Bd infects amphibians' skin and is thought to interfere with theirability to absorb water. Over 257 amphibian species are known to beaffected by Bd. Some species are very susceptible and die quickly whileothers, which are more resistant, are carriers of the pathogen.
Source: Imperial College London