The fungus Batrachochytrium dendrobatidis (Bd) causes a deadly skin disease in amphibians known as chytridryomycosis and has been severely affecting populations of frogs, toads, newts, salamanders and the like for years, virtually worldwide.
In recent years, a slowdown in this epizootic seemed to have been detected in areas of great amphibian biodiversity such as Africa, but a new study warns that Bd is still present and very active on this continent, a reality that endangers dozens of species.
Vance Vredenburg, lead author of the study and a professor at San Francisco State University and the Museum of Vertebrate Zoology at the University of California at Berkeley (United States), details that "Bd has become more frequent and widespread throughout the African continent since the year 2000". "This rapid increase may indicate that disease-induced amphibian decline and extinction may already be occurring in Africa without anyone knowing it," Vrendenburg says in a note released by his university. The results of the research have been published in the journal Frontiers in Conservation Science.
Vredenburg and colleagues first used quantitative real-time PCR to determine whether 2,972 museum specimens were infected with any known Bd strain. These were collected from Cameroon, Ethiopia, Kenya, Lesotho, Tanzania, and Uganda between 1908 and 2013 and were kept at the California Academy of Sciences, the Museum of Vertebrate Zoology at Berkeley, and the Museum of Comparative Zoology at Harvard University.
The researchers also tested skin samples from 1,651 live amphibians captured between 2011 and 2013 in Burundi, Equatorial Guinea, Cameroon, and the Democratic Republic of Congo for Bd.
Finally, they reviewed the scientific literature between 1852 and 2017 for records of the presence or absence of visible chytridiomycosis infection in amphibians across Africa. In total, the study analyzed patterns of pathogen presence in more than 16,900 specimens of various amphibian species.
In this study, they present estimates of the prevalence of Bd infection over time for Africa as a whole and for individual countries and regions.
The results show that the first Bd-positive amphibians in the dataset date from 1933 in Cameroon. The prevalence of infection in Africa as a whole remained below 5% for every decade between 1930 and 2000. But that same year, the prevalence of infection suddenly jumped to 17.2% and rose further to 21.6 % during the 2010s.
In countries for which more data is available, such as Cameroon, Kenya, Equatorial Guinea, and Burundi, this post-2000 jump in prevalence was even more pronounced: for example, up to 73.7% of samples were infected in Burundi.
An exception was South Africa, where positive samples were found as early as 1943, and the prevalence of infection was relatively stable (approximately 23.3%, including the local strain Bd-CAPE) from the 1970s until the end of the study, the researchers indicate. authors.
The study authors conclude that since 2000 there has been a large increase in the prevalence of Bd, which has been largely overlooked, "representing a new threat to amphibians throughout Africa; and the regions of greatest risk are East, Central and West Africa.
"We don't have a good idea why the change seems most evident around 2000 in Africa, that's later than other continents. This could be due to chance," Vredenburg said.
"But there is also the hypothesis that climate change-induced stress could make amphibians more susceptible to pathogens, or that the climate may be changing in such a way that pathogen climatic envelopes are becoming more common. It is It is likely that increased air travel by humans and freight transport is also to blame."
"The first thing to do is to find out if amphibians in the areas we identified as having a high prevalence of Bd are experiencing epizootics. What we need is a dynamic picture of the pathogen-host interaction," explains Professor Vredenburg.
"Eliminating this microscopic pathogen in nature is not possible, but we know that given the chance, many host species can survive. Since this pathogen appears to be globally transported by humans, we have a moral imperative to get involved and try to manage it." and mitigate its impact whenever possible," explains the lead author of this study.