Rapid spread of a deadly fungus threatens amphibians

The highly contagious fungus Batrachochytrium dendrobatidis (Bd) is killing off amphibians in many parts of the world. So far, comparatively little data has been available from Africa. Now a research team led by Vance Vredenburg from San Francisco State University reports that the fungus has been present there for many decades. However, it has spread considerably in recent years.

Bd primarily attacks the skin of frogs, newts and other amphibians and massively impairs their breathing. The disease caused by the fungus, chytridiomycosis, often leads to the death of the animals. Bd epidemics already existed in North America in the 1970s and 1980s. The chytrid fungus also spread in Central and South America as well as in Australia. With amphibians, it threatens an animal class that is already particularly endangered.

With a good 1200 species, around 16 percent of the approximately 8600 amphibian species known worldwide live in Africa. Studies had already shown that the chytrid fungus is also present here. In order to find out when, where and how the pathogen spread across the continent, Vredenburg and his team analyzed a good 4,600 amphibian samples collected since 1908. They tested samples from museum specimens as well as from living amphibians from a number of countries for the pathogen through genetic analysis. They also evaluated specialist literature dating back to the 19th century for indications of Bd infections in Africa.

The team found the earliest evidence of the pathogen in a sample that dates back to 1933 in Cameroon. A total of 3.2 percent of the amphibian samples evaluated up to 1999 were positive. In contrast, almost 19 percent of the samples taken since 2000 contained evidence of the pathogen, as the group writes in the journal Frontiers in Conservation Science.

After 2010, the proportion of Bd evidence continued to rise - to 21.6 percent of the analyzed samples. The results also show that the development varied in individual countries. Regions in East, Central and South Africa are particularly at risk.

"We show that Bd has become more common in Africa since 2000," Vredenburg is quoted as saying in a statement from the journal. "The rapid increase could signal that disease-related declines and amphibian extinctions in Africa may already be unfolding without anyone knowing."

The causes of the spread are not yet clear. "We cannot exactly explain this sudden increase in the number of cases," says Vredenburg. “Amphibians are very sensitive to temperature fluctuations.” He speculates that climate change could make them more susceptible to the pathogen. In addition, the increasing international travel and goods traffic promotes the international spread of the pathogen.

Bd has also been detected in Germany. However, there have been no large-scale analyzes here so far, says biologist Dirk Schmeller from the Institut National Polytechnique (INP) in Toulouse. The fungus Batrachochytrium salamandrivorans (Bsal), on the other hand, has been better researched. "The Bsal fungus attacks the skin of salamanders like salamanders," says Schmeller.

What can be done to preserve amphibians in Germany and other regions of the world? "First and foremost, we have to protect our ecosystems," says Schmeller. "Studies show that the fungi have greater problems multiplying in healthy ecosystems with clean water." His advice: People who often spend time near bodies of water should observe hygiene measures so that the pathogen is not spread. It can help to let wet bathing suits dry in the sun before jumping into the next lake.

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