A highly contagious and deadly fungal disease — considered the worst to affect wildlife in recorded history — is spreading and endangering amphibians across an entire continent.
The deadly 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 peel off, resulting in other symptoms such as lethargy, weight loss, and eventually heart failure. The disease is highly contagious and is transmitted through spores released by the fungus.
“The risks are significant,” said Vance Vredenburg, a professor in the Department of Biology at San Francisco State University. News week. “In fact, this disease is the worst in recorded history. It has infected more than 1,000 species of amphibians and led to the decline of about 500 species – dozens have gone extinct.”
Since the 1980s, the pathogen has spread, causing mass extinctions of amphibians around the world. It continues to spread to this day.
A study published in the journal Frontiers in conservation science has now discovered that the fungal pathogen is spreading across the African continent, a region scientists believed had escaped the worst of the disease.
But Vredenburg and his colleagues found that the disease has already established itself in Africa and its spread appears to have been overlooked in the region over the past two decades. The researchers found that it is likely to become more common and that amphibian declines and extinctions may already be happening under the radar there.
“Since 2000, Bd has spread throughout Africa and may threaten species across the continent,” Vredenburg said.
Africa is home to about 16 percent of known living amphibian species, but there are no described Bd epizootics — a disease event in an animal population that resembles an epidemic in humans — in Africa, even though the disease is known to occur there.
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The researchers said the lack of outbreak reports was likely due to lower Bd sampling efforts in Africa compared to other continents rather than a true absence of events.
The authors of the Limits study reached 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 captured between 2011 and 2013, and examined scientific data from the period 1852-2017.
They found a pattern of Bd emergence in Africa that largely began around the turn of the century. From 1852–1999, they saw low Bd prevalence (about 3 percent overall) and low geographic distribution across the continent.
But after 2000, they documented a sharp rise in prevalence, rising to more than 21 percent in the 2010s. In some countries, for which more data was available, the increase was even greater, for example in Burundi to more than 70 percent.
“We should be concerned,” Vredenburg said. “This is the first fungal pathogen to cause this level of mortality in vertebrates The last of us moment for humanity, we should try to learn from this to better understand what factors led a fungal pathogen to have such a profound effect on hosts.”