Scientists say a fungus that has devastated global frog populations has reached Madagascar, putting the island’s 500 endemic frog species in danger.

The amphibian-rich islands of Madagascar, Borneo and New Guinea have remained conspicuously free of the Batrachochytrium dendrobatidis (Bd) fungus, which has caused population crashes on every continent where amphibians occur.

But a Zoological Society of London (ZSL) team has discovered frogs carrying Bd in five areas in Madagascar between 2010 and 2014. In some places almost all frogs were infected. Their study, published in the journal Scientific Reports, indicates the fungus is now established and widespread on the island.

Scientists blame Bd, a chytrid fungus, for the decline or extinction of at least 200 species of frog. The International Union for the Conservation of Nature (IUCN) has called it “the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and its propensity to drive them to extinction”.

Study author Gonçalo Rosa said the strain of Bd had yet to be confirmed. It is possible that it is a form native to Madagascar and may not pose a threat to the local frogs. But some early tests suggest the presence of the global pandemic strain which can wipe out entire populations within a few years of arriving in an area.

“If we have a very virulent lineage, like this Global Pandemic Lineage, it can be a worry because we know that it can be really nasty to these frog populations and it’s been involved in massive declines,” said Rosa.

Map of all sites sampled for Bd. Circles represent sites of surveys conducted between 2005–2014, and red colouring highlights Bd-positive sites. Location name, site name, the month-year of detection and prevalence are provided for each location with Bd-positive occurrences. Photograph: ZSL/Nature

“We can expect that in Madagascar as well, but we just don’t know what species can be affected and the degree of susceptibility. We can predict that if there are native species being subjected to a novel pathogen, that should have a huge impact. But it’s just a guess, a worrying guess.”

Amphibians absorb water and salts through their skin. In a large number of species Bd causes chytridiomycosis, a dysfunction that causes the skin to overproduce keratin and harden. The disease often results in death. The team has not yet observed any frogs suffering these symptoms or the masses of dead frogs strewn along pond banks usually associated with a full blown chytrid outbreak.

It is likely some of Madagascar’s frogs could be resistant, as has occurred in other parts of the world. But should the disease take hold it will place added pressure on frog populations already squeezed by habitat destruction. Rosa’s team discovered two species carrying the disease, Mantidactylus pauliani and Boophis williamsi. Both are already critically endangered because of logging.

Madagascar is famous for its geographical and evolutionary isolation. The very isolation that until now has protected it from the spread of Bd. Of the world’s 6,500 frog and toads, around 7.5% are endemic to Africa’s largest island.

“If we are talking about impacts in terms of biodiversity, the loss in Madagascar would be much higher,” said Rosa.