Pathogen Spreads Through International Frog Trade

Allow me to set the scene with some facts. Batrachochytrium dendrobatidis (Bd) is a pathogenic fungus that causes chytridiomycosis, an infectious disease present in amphibians. Studies identified multiple distinct lineages of Bd, specifically Bd-BRAZIL, tracing its endemic origins and commercial spread globally through bullfrogs. Since then, chytridiomycosis has led to the drastic decline of 500 species and the extinction of 90 of them.

In particular, the reason behind its spread—for bullfrog leg consumption and farming purposes—stirred up some mixed feelings for me. Wandering through the humid streets of Nantong, China, I witnessed crates on top of crates of bullfrogs, mercilessly crammed together. “They’re alive.” My grandmother told me, pointing at the frogs, “They’ll kill them in front of you and snap off the legs. Can’t have buyers doubting the freshness.”

Standing there, all I felt was slight awe, a dash of pained sympathy, towards the creatures. Afterwards, she offered to buy one for a demonstration—to which I refused.

The priority of so-called fresh bullfrog meat is almost laughable when taken in consideration with other factors and the repercussions of wildlife trade. Live animals can host pathogens and shed fungi, bacteria or viruses into their environment, a risk that is far less prominent in dead animals. At the same time, security and health regulations on transporting these animals alive are not sufficiently well-defined, allowing the widespread proliferation of Bd.

I was struck by another detail. Bullfrog legs, considered a delicacy in Chinese cuisine, provide a stark contrast to the food that I am used to. Their prominence hinted at international trade networks moving these animals far from their native habitats. After all, bullfrogs originate from eastern North America, swampy regions of northern Mexico to southern Canada, and yet they are far more established in Asian cuisine.

This remarkable normal and abnormal sight at the market took on a new meaning after I discovered how easily they could carry Bd without showing symptoms.

Bullfrogs are optimal carriers for the fungus in this sense, for they are tolerant to the disease. These tolerant carriers highlight the danger of invisibility until we cannot truly quantify the extent of this issue.

This market I passed by was not an isolated occurrence but in reality, a situation replicated in many countries. Globally, careless wildlife trade transports pathogens stealthily and rapidly.

The transportation conditions are suboptimal. Live animals are packed and piled into containers. Under stressed, unsanitary conditions, their health deteriorates while disease risk increases. Water or resource restriction contributes to greater shedding of pathogens.

Bd-BRAZIL, the lineage in question, has been detected in North American and Asian bullfrogs despite its Brazilian roots. Once introduced, Bd-BRAZIL can decimate new populations, and what appears like ordinary trade is a conduit for pathogens capable of reshaping ecosystems.

We may overlook the relevance of amphibian species to our regular lives, and it is true that they do not directly influence us. Latching onto this view is harmful, though.

Frogs and other amphibians are actively involved in insect populations, plant communities and food webs, and when they die out, the whole ecosystem suffers substantially. Preserving not only frogs but all victims of unsafe wildlife trade guides genetic diversity and a thriving habitat.

As studies yield telling findings from increasingly advanced research and techniques, preventative actions need to evolve to match scientific knowledge. Modern-day import regulations and quarantine measures have not reached the necessary level.

Now that we can identify the root, spread and scale of live wildlife trade, we can follow by improving frequent pathogen screenings and safety measures. Native amphibian species around the world can flourish without concern over potentially fatal disease outbreaks.