A new study suggests that a deadly chytrid fungus, responsible for declines in hundreds of amphibian species, originated in Brazil and spread globally through the international bullfrog meat trade. Genetic and trade data point to bullfrogs farmed in Brazil as the key vector. Researchers urge stronger safeguards to prevent similar wildlife threats.
The chytrid fungus Batrachochytrium dendrobatidis, known as Bd, has caused population crashes in at least 500 frog and toad species worldwide. A study published in Biological Conservation challenges earlier claims, providing evidence that the Bd-Brazil strain emerged in Brazil around 1916, well before bullfrogs were introduced there in 1935 and the 1970s.
Led by scientists at Brazil's State University of Campinas (UNICAMP) in São Paulo, the research analyzed museum specimens, genetic data from frog farms, and international trade records. Of 2,280 amphibian specimens collected between 1815 and 2014 from global museums, 40 tested positive for Bd. The oldest confirmed cases were from 1915 in France's Pyrenees region, involving Alytes obstetricans frogs, while a 1964 specimen from Rio de Janeiro carried the strain.
"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," said Luisa P. Ribeiro, the study's first author and a former doctoral student at UNICAMP's Institute of Biology.
The team reviewed 3,617 frog meat trade routes across 48 countries, identifying eight primary paths for Bd-Brazil's spread. Brazil exported bullfrogs to the United States from 1991 to 2009, and the US sent them to South Korea in 2004 and 2008. The strain, less aggressive than the Asian-origin Bd-GPL variant, appears in both farmed and wild Brazilian species.
Funded by FAPESP as part of the project "From Natural History to the Conservation of Brazilian Amphibians," coordinated by Luís Felipe Toledo, the findings highlight the risks of wildlife trade. Experts call for stricter import rules, pathogen screening, quarantines, and global monitoring to protect amphibians from such invasions.
