“We humans can relax about becoming infected with Bd [the etiology of amphibian chytrid fungus disease]. Nevertheless we should be mourning the devastation of amphibian populations worldwide.”
Phillip K. Peterson, MD, professor of medicine emeritus, University of Minnesota
“Mycoviruses are widespread in the fungal kingdom, infecting over 20% of tested isolates.”
Hideki Kondo, Associate Professor, Institute of Plant Sciences and Resources, Okayama University, Japan
The pandemic annihilating amphibians is by far the most horrific of all the pandemics currently decimating animal species around the world. (See, “A True Horror Story: The Amphibian Chytrid Fungus Pandemic,” Germ Gems, March 29, 2023). The recent discovery of a virus named BdDV-1, within the fungus Batrachochytrium dendrobatidis that causes amphibian chytrid fungus disease, raises the question whether such viruses, called mycoviruses, could be used to curb the mass slaughter of frogs and salamanders. In this week’s Germ Gems’ post, I reintroduce readers to the terrible plight of amphibian populations and introduce the topic of mycoviruses.
The amphibian chytrid fungus pandemic (a recap). Chytridiomycosis is a fatal skin disease in amphibians caused by either Batrachochytrium dendrobatidis (nickname “Bd”) or Batrachochytrium salamandrivirans (nickname “Bsal”).Many experts consider Bd the most deadly invasive species on our planet; it is the species that is primarily decimating frog populations. As its name implies, Bsal is the species wiping out salamanders. Although frogs and salamanders have been hardest hit, researchers suggest that the fungus has precipitated declines of at least 501 amphibian species over the past five decades.
Some researchers believe that Bd evolved from a fungal ancestor over one billion years ago. It is found in much of the world, but its greatest impact has been in Central and South America, and Africa—the continent where it got its start. In 1993, Lee Berger, an Australian professor of biology, discovered that chytrid fungal disease was the cause of a massive mortality event of amphibians. Fortunately, Bd infections have yet to spill over to other animal species, including ours.
What are mycoviruses? Mycoviruses, also called mycophages, are viruses that are widespread in fungi, infecting more than 20% of infected isolates. The majority of mycoviruses have double-stranded RNA genomes. As mycophages have beneficial and detrimental effects on their fungal host, they are analogous to bacteriophages (“bacterial eaters”), viruses that infect bacteria.
In the early 1900s, the Franco-Canadian microbiologist Felix d’Herelle discovered bacteriophages and used them to treat patients with dysentery, bubonic plague and cholera. While the technique fell into disuse after the widespread adoption of antibiotics in the 1940s, research on the application of these “bacterial eaters” to the treatment of human bacterial infections continues to this day. (See, “Viruses That Eat Bacteria; Fighting Fire with Fire,” Germ Gems, June 10, 2020). To date, the application of mycoviruses has been as a biocontrol of plant pathogenic fungi. (See, “Fungal Viruses Unveiled: A Comprehensive Review of Mycoviruses,” Viruses, May, 2023).
What about BdDV-1? BdDV-1 is a mycophage that attacks the fungus Bd. According to an article in the 2024 issue of Current Biology, BdDV-1 is described as: “An endogenous DNA virus in an amphibian-killing fungus associated with pathogen genotype and virulence.” Early studies suggest that BdDV-1’s effects on the pathogenic properties of Bd are complex in that it decreases the growth of Bd but increases its virulence. Nonetheless, it demonstrates the potential of finding a mycovirus that reduces all the pathogenic properties of Bd.
It seems highly likely to me that if a search were to go on for beneficial mycophages similar to the search we’ve seen over the past century for bacteriophages that are beneficial to humans, our amphibian friends would be croaking for joy.
Initially, when limb abnormalities were first observed on frogs, and before any good science could be done, environmentalists claimed it was due to glyphosate. It is too common an occurrence that before good science can be done, the initial claims are believed by the public, and the later, good science is ignored.