Deadly, Highly Contagious Fungus Spreading in Amphibians 'Worst in History'

A highly contagious and deadly fungal disease—considered the worst to affect wildlife in recorded history—is spreading, placing amphibians across an entire continent at risk.

The fatal disease, known as chytridiomycosis, is caused by a microscopic fungus called Batrachochytrium dendrobatidis (Bd). Infection with this fungus has a devastating effect on frogs, toads and other amphibians.

The disease causes the skin of these animals to slough off while resulting in other symptoms like lethargy, weight loss, and, ultimately, heart failure. The disease is very contagious, transmitted via spores released by the fungus.

"The risks are significant," Vance Vredenburg, a professor in the Department of Biology at San Francisco State University, told Newsweek. "In fact, this disease is the worst in recorded history. It has infected over 1,000 species of amphibians and has caused declines in approximately 500 species—dozens have gone extinct."

Since the 1980s, the pathogen has spread and caused mass die-offs of amphibians around the world. It continues to spread to this day.

A study published in the journal Frontiers in Conservation Science has now found that the fungal pathogen is spreading across the African continent, a region that scientists thought had escaped the worst of the disease.

But Vredenburg and his colleagues found that the disease has already established itself in Africa and that its spread in the past two decades or so seems to have been overlooked in the region. The researchers found that it will likely become more prevalent, and that amphibian declines and extinctions might already be occurring there under the radar.

"Since 2000, Bd has spread throughout Africa and may threaten species across the entire continent," Vredenburg said.

Africa is home to around 16 percent of known living amphibian species but there are no described Bd epizootics—a disease event in an animal population akin to an epidemic in humans—in Africa, even though the disease is known to occur there.

The researchers said the lack of outbreak reports was likely due to lower Bd sampling efforts in Africa relative to other continents rather than a true absence of events.

The authors of the Frontiers study came to their conclusions after analyzing thousands of museum specimens collected from various locations in Africa between 1908 and 2013. They also tested skin swabs from live amphibians caught between 2011 and 2013, as well as examined scientific records from the period 1852-2017.

They found a pattern of Bd emergence in Africa beginning largely at the turn of the century. From 1852–1999, they observed a low Bd prevalence (around 3 percent overall) and low geographic spread on the continent.

But after 2000, they documented a sharp increase in prevalence, which rose to more than 21 percent during the 2010s. In some countries, for which more data were available, the rise was even higher—rising to more than 70 percent in Burundi, for example.

"We should be concerned," Vredenburg said. "This is the first fungal pathogen to cause this level of mortality in vertebrates. While this is not a The Last of Us moment for humanity, we should try to learn from this to better understand what factors have led to a fungal pathogen having such a profound effect on hosts."