Undetected by many, a fatal fungus that preys on the skin of frogs and other amphibians, called Batrachochytrium dendrobatidis or Bd for short, has been rapidly proliferating across Africa for the past two decades. This escalation of Bd on the continent has raised concerns that it could cause severe harm to amphibian populations in Africa, as it has done in other regions of the world.
Bd causes chytridiomycosis, a disease that leads to heart failure in amphibians, and has been identified as the cause of catastrophic declines in populations across the Americas and Australia. Vance Vredenburg from San Francisco State University highlights that “hundreds of species have been pushed to the brink of extinction by this single pathogen."
While researchers believe Bd originated in Asia and had spread to every continent by the late 1900s, its impact in Africa has not been well-documented. Although some studies indicate that it has been present on the continent since the 1930s, albeit at low levels, recent research suggests a surge in infection rates. However, this may simply be due to increased efforts to detect Bd compared to the past.
To further their research, Vredenburg and his team used museum collections of amphibians. Fungi and other parasites tend to be preserved along with the animals they inhabit, allowing researchers to analyze museum specimens to study the history of infectious diseases.
The team collected skin swabs from almost 3,000 specimens gathered in Africa over the past century. They also tested the skin of 1,651 wild amphibians and compiled thousands of records from other studies of specimens collected between 1852 and 2017. By combining all this information, they found that Bd was not widespread in Africa during the 1900s, with less than 5% of tested animals being infected. However, there was a significant change at the turn of the century, with the prevalence of Bd rising to about 20% across the continent in the early 2000s.
Although the cause of the surge in Bd prevalence is uncertain, Vredenburg suggests that trade and the associated movement of people and cargo may have played a role in spreading the fungus to new areas, as has happened in other parts of the world.
According to Breda Zimkus at Harvard University's Museum of Comparative Zoology, the team has compiled an impressive amount of new data to complement existing research. Zimkus notes that many regions that have experienced increases in Bd prevalence have also seen declines in amphibian populations, which the researchers suggest is no coincidence.
For instance, in Cameroon, where the team's data revealed that Bd prevalence rose to nearly 40% in the 2010s, amphibian populations of once-common species such as puddle frogs and long-fingered frogs have been rapidly declining.
Using the trends they uncovered, along with existing data on Bd's preferred climate and hosts, the researchers predicted where the fungus might spread next. They discovered that parts of western Africa that have yet to report chytridiomycosis cases could be at high risk.
Deanna Olson at the US Forest Service is pleased to see this type of risk assessment applied to Bd in Africa. She believes that such tools could assist managers in identifying the most critical areas for conservation planning, preventing further catastrophes for endangered species.
Vredenburg hopes that the findings will inspire more research into Africa's amphibians. According to him, these animals are highly under-studied, and if there were more information available, there would be more that could be done to help them.
Journal reference: Frontiers in Conservation Science