Evidence links frog trade to the spread of Bd-Brazil

The fungus Batrachochytrium dendrobatidis, Bd for short, is responsible for some of the largest losses of amphibian fauna recorded in modern times. A paper published in Biological Conservation by the team of Luisa Ribeiro and Luís Felipe Toledo at the Universidade Estadual de Campinas concerns one of its lineages — Bd-Brazil — and answers two questions: where it came from, and how it reached other continents.

The answer to the first changes the received picture. A prominent 2018 paper placed the pathogen's origin on the Korean Peninsula. The Campinas team dates the Brazilian lineage to around 1916 and locates it in Brazil, drawing among other things on 2,280 museum specimens collected between 1815 and 2014, of which 40 tested positive.

The second question is about routes. The authors analysed 3,617 frog-meat trade routes between 48 countries and identified eight principal dissemination pathways. The American bullfrog, a farmed species introduced to Brazil in 1935 and again in the 1970s, is the carrier in this picture: it can be infected without developing the disease, so a live animal in transit moves the pathogen without symptoms.

There are two conclusions for a European reader. First, a wildlife disease can travel the world along a food supply chain rather than along ecosystem boundaries — and then trade, not climate, sets the pace. Second, this is not a distant matter: the American bullfrog is listed in the European Union among invasive alien species of Union concern, precisely because of the risk to native amphibians.

The limits of the result are worth stating. Dating the lineage rests on genetic analysis and on museum material, and therefore on a sample that is not random: it comes from wherever somebody collected specimens and wherever those specimens were kept. The finding shifts the most probable place and time of origin — it does not close the question.

Bd is not a single thing. The name covers several genetic lineages with different histories and different virulence, and what separates them determines the outcome of any meeting with a local fauna. The global lineage, BdGPL, accounts for most recorded die-offs — regional lineages such as Bd-Brazil can be tolerated within their own range by species that have long coexisted with them. Moving such a lineage to another continent, however, means introducing it to amphibians that have had no time to adapt.

That is why mapping the transport routes matters here as much as the dating. Closing a trade route is something that can be done — reversing the spread of a pathogen in the environment is not. The authors identify eight routes rather than one, and that too is a result — it shows the problem has no single point at which it could be solved.

Museum collections played a part in this study that no monitoring network founded today could play. A specimen collected in 1916 was not collected in order to detect a fungus nobody then knew about — and yet it contains one. Without herbaria and zoological collections, the question of when this began would have no answer.

Hypothesis status — 29 August 2026

The article appeared online on 17 October 2025, while its journal issue is dated 2026. The authors combine museum specimens, global occurrence records, genotyping, phylogeny and historical trade routes. Their results are consistent with Bd-Brazil originating in Brazil and spreading through the international bullfrog trade, but they do not follow a single infected shipment from a farm to a newly affected population. “The trade carried it” is therefore too categorical. The paper supports screening, quarantine and denser sampling, while leaving uncertainty about the exact routes and dates of transmission.