When populations of newts and salamanders experienced a sudden, massive crash in the Netherlands last years, scientists wanted to know why. Upon investigation, they revealed something horrifying: The culprit is Batrachochytrium salamandrivorans, a previously unknown fungus brought to Europe by humans. Many species of newts and salamanders are at risk, though frogs and caecilians appear to be safe.

The fungus followed a weird path to where it is today. It’s believed to have originated in East Asia, with instances of it being found as early as 1861. However, animals in that reason show no signs of disease, indicating that the fungus has been around for some time. Due to globalization and the demand for “exotic” animals, it’s suspected that the intercontinental amphibian trade brought it to Europe.

“When a disease has been around for a long time, animals develop resistance to it. Globalisation has resulted in the movement of humans and animals all across the world, bringing pathogens into contact with hosts that haven’t had the opportunity to establish resistance. As a consequence, pathogens like B. salamandrivorans that are brought to a new environment can very rapidly threaten many species with extinction,” said Professor An Martel of Ghent University in Belgium.

It’s hard to overestimate the magnitude of the international amphibian trade. It’s estimated that over two million Chinese fire belly newts were smuggled into the U.S. between 2001 and 2009. That’s bad news for any native populations not familiar with the fungus: The researchers say it’s easily transmitted between species through casual contact.

Thus far, the disease has only been found in the Netherlands and Belgium, though researchers say spread is inevitable and will happen soon. They note that the great crested newt, a protected species in Europe, is particularly vulnerable to the fungus and dies rapidly once infected. All in all, 5,000 species from four continents were screened to determine the risk of infection.