Amphibian apocalypse: Study finds multiple strains of a lethal fungal pathogen threaten frogs in Africa

Multiple strains of a lethal fungal pathogen are invading frog populations across Africa, posing severe risks to amphibians, according to a new study.

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Pandemics in amphibians — caused by the pathogen Batrachochytriumdendrobatidis (Bd) — have resulted in biodiversity loss at a global scale, particularly in the African continent, said the study published on March 15, 2023, in Frontiers in Conservation Science.

Bd causes chytridiomycosis, a contagious and lethal disease that has driven hundreds of species worldwide to extinction.

Bd-induced pandemic is not limited to isolated outbreaks; instead, it represents a broad pattern of synchronised emergence across the entire continent, noted the researchers.

From 1852–1999, they found low Bd prevalence (3.2 per cent) and limited geographic spread. Still, after 2000, a sharp increase was documented in prevalence (18.7 per cent), geographic spread and lineages responsible for the emergence in different regions.

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The pattern was more noticeable in several countries from where the researchers could collect more comprehensive data.

For instance, in Cameroon, they could find only one Bd positive in samples collected until 1999. But in the next decade, the 2000s, the frequency of Bd occurrence rose to 11.0 per cent, followed by an increase of 36.2 per cent in the 2010s.

In Cameroon, “the average Bd infection intensity also increased over time and in the most recent samples, maximum values surpassed a threshold infection intensity associated with chytridiomycosis-caused mortality,” the paper read.

Likewise, in Kenya, the frequency of Bd occurrence was zero or very low in the first four decades of the study period. The highest frequency in these early decades was in the 1970s, at 5.2 per. It increased approximately six-fold in the 2000s, at 31.5 per cent. The average Bd infection intensity in Kenya also increased during this same period.

Bd risk to amphibians was highest in much of eastern, central, and western Africa, the document added. Burundi, in eastern Africa, had the highest frequency of Bd infections after 2000, at 73.7 per cent.

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Africa harbours nearly 16 per cent of known living species of amphibians and multiple lineages of Bd (including Bd-CAPE and Bd-GPL) have been found to infect these hosts in the wild.

Bd-CAPE has been detected in Cameroon and was found to be widely present in South Africa, while the Bd-GPL lineage has invaded almost every region of Africa.

The research was led by Sonia Lorraine Ghose from the University of California. Her team gathered 16,920 original and previously published records between 1852 and 2017 from 36 African countries.

The first known chytridiomycosis epizootics occurred in western North America in the late 1970s and early 1980s; then in Central America and Australia in the late 1990s and in South America in the early 2000s.

Genetic analyses have shown that besides the strain Bd-GPL, thought to be responsible for most chytridiomycosis epizootics, at least four other, possibly less virulent strains from South Korea, Switzerland, South America and southern Africa are currently in prevalence.

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