Ignored fungal disease could be causing a frog epidemic globally

Tuesday March 28 2023
a frog

Scientists say frogs could be dying from a fungal infectious disease called chytridiomycosis that has largely gone ignored on the African continent. PHOTO | RODRIGO BUENDIA | AFP


Have you been hearing less and less croaks from the neighbourhood swamp or stream? Scientists say frogs could be dying from a fungal infectious disease called chytridiomycosis that has largely gone ignored on the continent. And it might have something to do with climate change.

Billed as one of the worst vertebrate diseases in recorded history, it is believed to have begun spreading widely in Africa in 2000 and may be causing overlooked epizootics, the equivalent of an epidemic in humans.

According to a paper in the Journal Frontiers in Conservation Science, the disease has already wiped out hundreds of species of amphibians around the world.


This picture from the Department of Environmental Studies at Delhi University on June 14, 2016 shows Bombay Night frogs in Dorsal straddle. PHOTO | AFP

Up to 41 percent of amphibians are currently threatened with extinction.

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“Only species living in Africa seemed to have been relatively spared from the scourge of chytridiomycosis,” said the paper.

“Disease-driven declines and extinctions of amphibians may already be occurring in Africa without anyone knowing about it,” said Dr Vance Vredenburg, study author and professor at the San Francisco State University.

Chytridiomycosis is highly contagious since it doesn’t need an animal vector to spread, and spores can thrive in cool moist habitats.

The fungus is capable of causing sporadic deaths in some amphibian populations and 100 per cent mortality in others.

Key for ecosystem

“The disease rarely kills tadpoles but often kills adults, in which it causes the sloughing off of skin, lethargy, weight loss and ultimately cardiac arrest,” explained the researchers.

Frogs like other amphibians are important for our ecosystem and ecological balance.

They are good for pest and disease control as they eat untold billions of insects each year including mosquitoes and are economically valuable to agricultural pests.

They also provide a critical food source for birds, fish, snakes and other wildlife maintaining balance within the food web. Tadpoles filter our drinking water by eating algae, helping regulate blooms and reducing the chances of algal contamination.


Fish swim off a coral reef in Indian Ocean off the coastline of Mombasa. PHOTO | NMG

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But the most important contribution frogs make is as environmental indicators.

The disease study analysis

The study analysed patterns of pathogen presence in over 16,900 amphibian specimens from Kenya, Tanzania, Uganda, Ethiopia, Cameroon, Lesotho, Burundi, Equatorial Guinea, Cameroon and the Democratic Republic of Congo.

The results show that the earliest disease-positive amphibian in the dataset dated 1933 in Cameroon.

The infection prevalence across Africa stayed below five percent up to 2000 when it suddenly jumped to 17.2 percent and increased further to 21.6 percent during the 2010s.

In countries where more data is available such as Cameroon, Kenya, Equatorial Guinea, and Burundi, this jump was even more pronounced. For example, up to 73.7 percent of samples were infected in Burundi.

“But there is also a hypothesis that climate change-induced stress could make amphibians more susceptible to pathogens or that the climate may be changing such that the climate envelope for the pathogen is becoming more common. It’s likely that increased air travel of humans and cargo is also a culprit.”