There are lots of brown tree frogs, like this southern brown tree frog (Litoria ewingi) found in Melbourne, Australia. But wait till you see the chocolate tree frog! Image by Matt from Melbourne, Australia
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A pathogenic fungus that has wiped out hundreds of amphibian species worldwide started its global journey in Brazil. Genetic evidence correlated with trade data demonstrates how the fungus hitchhiked across the world via international frog meat markets.
These findings, from Fundação de Amparo à Pesquisa do Estado de São Paulo, raise urgent concerns about how wildlife trade can spread hidden biological threats.
Frog meat market
Millions of wild frogs are killed and exported each year. The majority of these are sent into the European Union where, in some places, frogs legs are considered a delicacy. However, there is little transparency as to how this trade operates.
The reason why the export market has grown was a consequence of Europe’s demand for frog legs. This has not only threatened the animals in Europe but this extended worldwide because the demand outstripped supply, leading to significant reductions in European populations.
Fungal spread
A consequence of this animal trade has been the spread of the chytrid fungus (Batrachochytrium dendrobatidis). This organism has been a major factor behind the worldwide decline of amphibians.
The fungal pathogen causes the disease chytridiomycosis. This damages the skin of frogs, toads, and other amphibians, disrupting their balance of water and salt and eventually causing heart failure.
Chytridiomycosis has been linked to dramatic population declines or extinctions of amphibian species in western North America, Central America, South America, eastern Australia, east Africa (Tanzania), and Dominica and Montserrat in the Caribbean.
Furthermore, scientists have identified multiple genetic variants of this disease causing fungus across different regions. Together, these strains have already contributed to population crashes in at least 500 species of frogs and toads.
Bullfrog population decline
New research has linked the international spread of the fungal pathogen to the commercial trade of bullfrogs (Aquarana catesbeiana), a species native to North America that is widely farmed for food.
Bullfrogs were first brought to Brazil in 1935, with another introduction occurring in the 1970s. These movements created new pathways for the fungus to travel across borders.
The study combined multiple lines of evidence. Researchers reviewed existing scientific literature, examined museum specimens from around the world, analysed fungal genetics from Brazilian bullfrog farms, and studied bullfrogs sold internationally.
To reconstruct the fungus’s historical distribution, international collaborators examined 2,280 amphibian specimens collected between 1815 and 2014 and stored in zoological museums worldwide. The researchers also analysed historical trade records, fungal genetics from Brazilian frog farms, and genetic data from bullfrogs sold in foreign markets.
The scientists examined 3,617 frog meat trade routes involving 48 countries. Of these, 12 countries acted solely as exporters, 21 as importers, and 15 served both roles. By combining trade data with genetic evidence and the timing of fungal relatedBrazil detections, researchers identified the most likely paths by which the strain spread.
Together, these data point to Brazil as the source of the strain and identify the global frog meat trade as the main route of its spread.
Next steps
The researchers conclude that their results highlight the need for stronger preventive actions. These include stricter import regulations, routine pathogen screening, quarantine measures, and coordinated global monitoring to better protect native amphibian species from future outbreaks.
The research is part of the project “From Natural History to the Conservation of Brazilian Amphibians,” supported by the São Paulo Research Foundation (FAPESP). The study appears in the journal Biological Conservation, titled “Origin and global spread of an endemic chytrid fungus lineage linked to the bullfrog trade.”
