The fungus Batrachochytrium dendrobatidis has performed a serious position within the worldwide decline of frogs and toads. Its origins have been investigated in a research performed by scientists from the State College of Campinas, which examined the place this damaging pressure first emerged.
The chytrid fungus (Batrachochytrium dendrobatidis), generally generally known as Bd, is well known as a significant component behind the worldwide decline of amphibians. Scientists have found that the pathogen exists in a number of genetic varieties, every discovered in several areas of the world. Collectively, these strains have contributed to inhabitants losses affecting at the very least 500 species of anuran amphibians, including frogs and toads.
Researchers believe the worldwide movement of Bd is closely tied to the commercial trade in bullfrogs (Aquarana catesbeiana), a species native to North America that is raised for food in many countries. Bullfrogs were first brought to Brazil in 1935, followed by another introduction several decades later during the 1970s.
One particular variant, known as Bd-Brazil, was first identified in the country in 2012 and named accordingly. Its origins were later questioned after a 2018 study published in the journal Science proposed that the strain may have emerged on the Korean Peninsula. As a result, the genotype was subsequently referred to as Bd-Asia-2/Bd-Brazil.
Evidence Pointing Back to Brazil
New findings published in the journal Biological Conservation, with support from FAPESP, provide strong evidence that the strain originated in Brazil. The research, carried out by scientists at the State University of Campinas (UNICAMP) in São Paulo state, shows that although Bd-Brazil has been detected in the United States, Japan, and the Korean Peninsula, its earliest roots trace back to Brazil.
According to earlier research published in Molecular Ecology in 2014, the Bd-Brazil strain was already present in Brazil by 1916, well before bullfrogs were introduced to the country. That study analyzed genetic material from frog specimens preserved in museum collections dating back to the 19th century, revealing the long-standing presence of the fungus.
The new study combined evidence from past scientific research with records of Bd found in museum amphibians worldwide, genetic testing of fungi from Brazilian bullfrog farms, and analyses of bullfrogs sold internationally. Taken together, these data indicate that the strain most likely spread from Brazil to other parts of the world through the global trade in frog meat, an industry in which Brazil plays a leading role.
“This genotype is highly prevalent in different native Brazilian species, with very old records. When we look elsewhere, the records are much more recent and occur only in bullfrogs and other exotic species. Here, however, the strain is present both in frog farms and in the wild, including some native species that do not develop the disease,” says Luisa P. Ribeiro, the first author of the study. She conducted the study as part of her doctoral research at the Institute of Biology (IB) at UNICAMP with a scholarship from FAPESP.
The work is part of the project “From Natural History to the Conservation of Brazilian Amphibians”, which is supported by FAPESP and is coordinated by Luís Felipe Toledo, who is a professor at IB-UNICAMP and Ribeiro’s doctoral advisor.
“We were unable to identify the exact strain in a large sample of amphibians deposited in museums, since conservation isn’t always ideal for maintaining this information. Therefore, we only identified the presence or absence of the fungus in these individuals and sought other evidence that could indicate whether or not Bd-Brazil originated in Brazil,” says Toledo.
History of a fungus
To assess its historical distribution, foreign collaborators examined 2,280 amphibian specimens collected between 1815 and 2014 and deposited in zoology museums around the world.
“Even without knowing the strain, we found records older than those previously reported in the literature and presented a review of historical records of Bd worldwide,” says Ribeiro, who is currently pursuing postdoctoral studies at the Federal University of São Paulo (UNIFESP) with a fellowship from FAPESP.
Of the 2,280 museum specimens tested, 40 tested positive for Bd. The oldest record of infection by the fungus was found in five individuals of the species Alytes obstetricans. These frogs were collected in 1915 in the Pyrenees in France and are the oldest known in the country. The second oldest specimen was a frog of a species currently found in Rio de Janeiro, Megophrys goeldii, collected in 1964.
To reinforce the hypothesis of dissemination from Brazil to the rest of the world through the export of bullfrogs, the researchers resorted to historical records of trade in the species, genotyping of the fungus in frogs from Brazilian frog farms, and genetic analyses of bullfrogs from markets outside the country.
Bd-Brazil is prevalent in Brazil, with more than half of the occurrences found on frog farms. It is less virulent than the second most common strain, Bd-GPL, which probably originated in Asia.
The researchers analyzed 3,617 international frog meat trade routes involving 48 countries. Only 12 were identified as exporters, 21 as importers, and 15 as both. They integrated data from routes involving countries with confirmed Bd-Brazil occurrences, the earliest detection dates in each country, and genetic evidence from commercialized bullfrogs. Thus, the most plausible dispersion routes for the Brazilian strain could be established.
The hypothesis of spread from Brazil involved eight identified routes. Brazil exported directly to the United States between 1991 and 2009, and the United States exported to South Korea in 2004 and 2008. Since there are no documented exports from the Asian country where Bd-Brazil was confirmed to other affected countries, it is highly likely that Brazil is indeed the origin of the genotype.
The authors conclude that these results underscore the urgent need for preventive measures, such as import controls, pathogen screening, and quarantine protocols, to safeguard native species, with global regulation and monitoring.
Reference: “Origin and global spread of an endemic chytrid fungus lineage linked to the bullfrog trade” by Luisa P. Ribeiro, Julia R. Ernetti, Joice Ruggeri, Thomas S. Jenkinson, Adeline Loyau, Helen Butler, Tina Cheng, Dirk S. Schmeller, Timothy Y. James and Luís Felipe Toledo, 17 October 2025, Biological Conservation.
DOI: 10.1016/j.biocon.2025.111547
Funding: São Paulo Research Foundation
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