The chattered fungus (), commonly generally known as BD, is well known as a significant factor behind the worldwide decline of amphibians. Scientists have identified several genetic types of the disease brought on by the fungus in several regions. Together, these stresses have contributed to population declines in at the very least 500 species of frogs and toads.
Researchers have linked the international spread of BD to the industrial trade in bullfrogs (), a North American species that’s widely farmed for food. Bullfrogs were first delivered to Brazil in 1935, with one other introduction within the Seventies. These movements created recent routes for fungi to travel across borders.
A controversial origin revisited
A selected strain, generally known as BD Brazil, was named after it was identified within the country in 2012. Its origins were soon disputed. In 2018, a study published within the journal suggested that the strain actually emerged on the Korean Peninsula. Consequently, it was renamed BD-ASIA-2/BD-Brazil.
New findings now challenge this conclusion. A study published within the journal Biological Conservation supported by FAPESP provides strong evidence that the strain originated in Brazil. The research was led by scientists from the State University of Campinas (Unicamp) in São Paulo, Brazil. The strain has since been detected within the United States, Japan, and the Korean Peninsula.
Evidence from museums and genetic records
According to earlier research published in 2014, BD Brazil was already present in Brazil by 1916, about 20 years before bullfrogs were introduced. The study analyzed frog specimens preserved in museums because the nineteenth century and identified fungal strains through genetic testing.
The recent study found several lines of evidence. The researchers reviewed the present scientific literature, examined museum specimens from all over the world, analyzed fungal genetics from Brazilian bullfrog farms, and studied internationally traded bullfrogs. Together, these data point to Brazil because the source of the strain and discover the worldwide frog meat trade because the most important route of its spread.
“These genotypes are very common in different Brazilian species, with very old records. When we look elsewhere, the records are very recent and only in bullfrogs and other exotic species. However, the strain is also present in frog farms and in the wild, including some indigenous species that do not develop the disease,” Luis P. Ribeiro says, “Louis P. He conducted this research during his doctoral studies on the Institute of Biology (IB) at UNICAMP with funding from FAPESP.
This work is an element of the project “From Natural History to the Conservation of Brazilian Amphibians,” supported by FAPESP and supported by Luis Felipe Toledo, professor of IB Unicamp and Ribeiro’s doctoral advisor.
Tracing fungi through history
“We were unable to identify the exact strain in a large sample of amphibians collected in museums, because preservation is not always ideal to preserve this information. Therefore, we only identified the presence or absence of the fungus in these individuals and looked for other evidence that might indicate whether or not Bd Brasil originated in Brazil,” says Toledo.
To reconstruct the historical distribution of the fungus, international partners examined 2,280 amoeba specimens collected between 1815 and 2014 and stored in zoological museums all over the world.
“Even without knowing the strain, we found records older than those previously reported in the literature and reviewed historical records from BD Worldwide,” says Federes, who’s now a postdoctoral researcher on the Federal University of São Paulo (UNIFES) with support.
Of all of the samples analyzed, 40 tested positive for BD. The earliest confirmed cases got here from five frogs of the species collected in 1915 within the Pyrenees region of France. These are the oldest affected specimens on this country. The second earliest record involved a frog of the species, currently present in Rio de Janeiro, collected in 1964.
Mapping Global Trade Routes
To further test the idea that BD spreads internationally through Brazilian bullfrog exports, the researchers analyzed historical trade records, fungal genetics from Brazilian frog farms, and genetic data from bullfrogs sold in foreign markets.
Bd Brazil is widespread inside Brazil, with greater than half of records from frog farms. The strain is taken into account less aggressive than BDGPL, the second commonest strain, which probably originated in Asia.
The team examined 3,617 frog meat trade routes involving 48 countries. Of these countries, 12 acted solely as exporters, 21 as importers, and 15 played each roles. By combining trade data with genetic evidence and the timing of detection of Bd Brazil, the researchers identified potential routes by which the strain spread.
Eight primary dispersal pathways were identified. Brazil exported bullfrogs on to the United States between 1991 and 2009, while the United States exported to South Korea in 2004 and 2008. Because there are not any records of exports from South Korea to other affected countries, these results strongly support Brazil because the most important source of this strain.
A call for stronger security measures
The researchers conclude that their findings highlight the necessity for stronger preventive measures. These include stricter import rules, routine pathogen screening, quarantine measures, and coordinated global surveillance to higher protect native amphibian species from future outbreaks.