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Deadly fungus threatens African amphibians

At a time when infectious diseases play a significant role in the media and popular culture – due to the Covid-19 pandemic and TV shows such as “The Last of Us,” in which a deadly, brain-infecting fungus is wiping out most of the human population – many scientists around the world are trying to better understand how viruses, bacteria, and fungi affect not only humans but also other animals. 

A team of researchers led by the San Francisco State University (SFSU) has recently investigated the emerge and spread of a deadly fungus (Batrachochytrium dendrobatidis or Bd) among amphibians in Africa. Since it affects the skin of amphibians, which is much more important for their survival than it is for humans, this pathogen is highly detrimental for amphibians worldwide, currently contributing to a significant loss in biodiversity.

“When [amphibian] skin starts to change thickness, it basically creates a condition where they can’t maintain their internal processes and they die,” said study co-author Eliseo Parra, a biologist at SFSU. “If infecting a mammal, it might affect your fingernails or something you wouldn’t even notice, but amphibians (frogs, salamanders) use their skin to breathe. It’s a very critical part of their body.”

Since this fungus appears to be lethal for many amphibian populations but not others, the experts aimed to better understand this pathogen’s emergence, evolution, and prevalence, focusing on under-studied areas in Africa. Through a combination of methods including the testing of thousands of frog specimens, the examination of previous scientific studies of this disease, and the genotyping of Bd lineages, the researchers mapped how the fungus interacted with amphibians across the African continent over the past 165 years.

The analyses revealed that, until 2000, there was low prevalence and limited spread of the disease in Africa. Afterwards, prevalence spiked from 3.2 percent to 18.7 percent and Bd became more widespread geographically and increasingly deadly for a large number of amphibians. The scientists identified two main lineages of the fungus in Africa: a global, more dangerous lineage, and a local lineage which, although it was previously thought to be more benign, new evidence shows that it can also be quite destructive. By using this data, the researchers created a model estimating that eastern, central, and western Africa are the regions most vulnerable to Bd.

“We’re trying to extend our findings and make predictions about what could happen in the future. It’s the best way to make our study worth the work,” said senior author Vance Vredenburg, the Associate Chair of the Department of Biology at SFSU. “There are nearly 1,200 amphibian species in Africa. We wanted to say where are the riskiest places for outbreaks. Those will probably be the places where you have the most hosts in one place.”

“It’s very important to note that Bd didn’t spread worldwide without humans helping in one way or another. It’s not the first pathogen that affects hundreds of species worldwide and it’s not going to be the last,” concluded co-author Hasan Sulaeman, a biologist at the same university.

The study is published in the journal Frontiers in Conservation Science.

By Andrei Ionescu, Staff Writer

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