Could a new virus put an end to the global amphibian pandemic?

A team of scientists led by the University of California, Riverside (UCR) may have found a potential weak point in the fight against a fungus decimating frog and toad populations across the globe. The study focused on a virus that infects the fungus responsible for the global amphibian pandemic, offering a possible avenue for intervention.

Declining amphibian species worldwide

The culprit, a fungus known as Batrachochytrium dendrobatidis or Bd, attacks the skin of frogs and toads, leading to heart failure. It is implicated in the decline of over 500 amphibian species worldwide and the possible extinction of 90 species, including the yellow-legged mountain frogs in the Sierras and the Panamanian golden frog.

However, the recent discovery of a virus that infects Bd not only contributes for understanding how fungal pathogens emerge and spread, but also sparks hope for halting what is currently termed a global amphibian pandemic.

Frogs as bioindicators of climate change 

“Frogs control bad insects, crop pests, and mosquitoes. If their populations all over the world collapse, it could be devastating,” said co-author Mark Yacoub, a doctoral student in microbiology at UCR. 

“They’re also the canary in the coal mine of climate change. As temperatures get warmer, UV light gets stronger, and water quality gets worse, frogs respond to that. If they get wiped out, we lose an important environmental signal.”

Discovery of the Bd-infecting virus

The rise of Bd as a threat to amphibians began in the late 1990s, marking the start of widespread fatalities among frog populations. The discovery of the Bd-infecting virus came as Yacoub and Jason Stajich, a UCR microbiology professor, were analyzing the population genetics of Bd to trace its origins and mutations.

During their research, they employed DNA sequencing technology and identified sequences within the data that did not match Bd’s DNA. 

“We wanted to see how different strains of fungus differ in places like Africa, Brazil, and the U.S., just like people study different strains of COVID-19,” Stajich said. “We realized these extra sequences, when put together, had the hallmarks of a viral genome.” 

This discovery is particularly significant as previous attempts to find viruses associated with Bd had failed, partly due to the fungus’s complex life cycle and the difficulty of studying it in laboratory conditions.

Single-stranded DNA virus

Interestingly, the virus identified is a single-stranded DNA virus, contrasting with the RNA viruses typically found infecting fungi. The presence of the virus in the fungal genome varies, with infected strains displaying different behaviors from those uninfected. 

“When these strains possess the virus they produce fewer spores, so it spreads more slowly. But they also might become more virulent, killing frogs faster,” Stajich explained.

The next steps involve cloning the virus to see if artificially infecting Bd strains could lead to reduced spore production. This distinction between infected and uninfected fungal strains emphasizes the need for comprehensive studies across multiple strains.

Amphibians may evolve resistance to the fungus

The research team is now focused on understanding how the virus infects the fungus and penetrates its cells, crucial knowledge for potentially engineering the virus to aid amphibians. 

Additionally, there’s hope that, similar to some emerging resistance to COVID-19, amphibians might slowly build immunity to Bd. 

“Like with COVID, there is a slow buildup of immunity. We are hoping to assist nature in taking its course,” Yacoub concluded, highlighting the potential for natural resistance alongside scientific intervention to combat this deadly fungal pathogen.

More about global amphibian pandemic

The global amphibian pandemic caused by the Batrachochytrium dendrobatidis (Bd) fungus. Its spread has been facilitated by global trade and environmental changes, affecting diverse ecosystems across continents.

Bd fungus

First identified in the late 1990s, the Bd fungus has since been recognized as one of the most devastating pathogens to biodiversity. It thrives in cool, moist environments, making mountainous regions particularly vulnerable. The disease disrupts the electrolyte balance and skin functions in amphibians, leading to heart failure and death.

Mitigation

Efforts to combat the pandemic have included breeding programs in biosecure facilities, reintroduction of species to their natural habitats with improved resistance or reduced pathogen presence, and environmental management to reduce the impact of the disease. 

Despite these efforts, the chytridiomycosis pandemic continues to pose a significant threat to amphibian populations, highlighting the challenges of managing disease in wild populations and the need for global conservation initiatives.

The study is published in the journal Current Biology.

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