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A Fungus Behind Amphibian Declines
A deadly fungus blamed for the decline of hundreds of amphibian species worldwide may have originated in Brazil and spread through the international trade in frog meat, new research suggests.
The chytrid fungus Batrachochytrium dendrobatidis (Bd) has devastated frog and toad populations across continents, contributing to crashes in at least 500 species. Scientists have long debated its origin, with earlier studies pointing to Asia. But a new study published in Biological Conservation argues that a strain known as Bd‑Brazil first appeared in the country and later traveled abroad through bullfrog exports.
Bullfrog Trade As a Pathway
Bullfrogs (Aquarana catesbeiana), native to North America, were introduced to Brazil in 1935 and again in the 1970s for farming. Researchers say these movements created pathways for the fungus to cross borders. Genetic evidence, museum specimens, and trade records all point to Brazil as the source.
“This genotype is highly prevalent in native Brazilian species, with records dating back more than a century. Elsewhere, detections are much more recent and largely confined to bullfrogs and other exotic species,” said Luisa P. Ribeiro, lead author of the study conducted at the State University of Campinas (UNICAMP).
Debating the Fungus’s Origins
The Bd‑Brazil strain was first identified in 2012, but its origin soon became contested. A 2018 study suggested it emerged in Asia, leading to its renaming as Bd‑Asia‑2/Bd‑Brazil. The new findings, however, challenge that conclusion, presenting strong evidence that the strain originated in Brazil before spreading abroad.
Evidence from Museums and Genetics
The team examined 2,280 preserved amphibians collected between 1815 and 2014 from museums worldwide. Forty tested positive for Bd, including specimens from France in 1915 and Brazil in 1964. Trade data revealed 3,617 routes for frog meat, involving 48 countries, with Brazil exporting directly to the United States and the U.S. later shipping to South Korea.
Mapping Global Trade Routes
Bd‑Brazil is now widespread in Brazil, particularly in frog farms, and has been detected in the United States, Japan, and Korea. While considered less aggressive than the Bd‑GPL strain thought to have originated in Asia, researchers warn that its spread underscores the risks of wildlife trade.
Call for Stronger Safeguards
The study calls for stronger safeguards, including stricter import rules, routine pathogen screening, quarantine measures, and coordinated global monitoring to protect amphibians from future outbreaks.
