Deadly Fungus Detected in Southeast Asia's Amphibian Trade

Mar. 6, 2013 — A team of scientists led by the Wildlife Conservation Society (WCS) and the National University of Singapore (NUS), revealed in a new study, for the first time, the presence of the pathogenic chytrid fungus (Batrachochytrium dendrobatidis) in amphibians sampled in Singapore. And the American bullfrog may be a central player in the spread of the disease.

The study appears in the current issue of the journal EcoHealth, and is the first to consider the role that Southeast Asia's commercial trade plays in the spread of amphibian pathogens.

Demand for amphibians through local and international trade is high and fueled by use of frogs as pets, food, bait, and as a source of traditional 'medicine.' More than 40 percent of amphibian species are in decline globally due, not only to chytrid fungus, but also overharvesting, competition from invasive species, habitat loss, pollution, and climate change.

In the study, scientists collected samples from 2,389 individual animals in Lao PDR, Cambodia, Vietnam, and Singapore at 51 different sites including farms, locally supplied markets, pet stores, and from the wild.

Continued:  http://www.sciencedaily.com/releases/2013/03/130306133815.htm

Despite Deadly Fungus, Frog Imports Continue – via Herp Digest

By John Upton, San Francisco, 4/7/12, Bay Gazette, Reprinted in NYTimes U.S. Blog.

A clerk serving Cantonese-speaking customers at a cluttered market in San Francisco’s Chinatown reached into a tub of American bullfrogs. She drew a one-pound frog from the top of the pile. She whacked its head, sliced its neck and placed its body in a plastic grocery bag.

A Chinatown seafood-store sign warns that releasing frogs into the wild is illegal.

More than half the frogs imported into San Francisco every year carry the chytrid skin fungus.

The frog cost about $4. If it was sautéed, stir-fried or cooked in a clay pot and served with rice and vegetables, it could provide enough poultry-flavored white meat for a meal for at least two people.

Tests on the bullfrog by Raul Figueroa, a researcher at San Francisco State University, confirmed that it was infected with an invisible but virulent fungus. The chytrid skin fungus Batrachochytrium dendrobatidis, or B.d., is harmless to humans but may have wiped out hundreds of amphibian species. Two other bullfrogs that The Bay Citizen bought from other Chinatown markets also tested positive.

The disease appears to affect only amphibians, and some species are immune to its effects while others succumb rapidly. It causes the amphibians’ skin to thicken and leads to cardiac arrest.

American bullfrogs are native to eastern North America but are reared in factory farms around the world. Two million bullfrogs are imported into the Bay Area every year, according to federal import records, and millions more are shipped to other major cities.

Scientists and conservationists fear that the global trade could lead to the extinction of countless species of frogs and salamanders. Amphibians play subtle but substantial roles in California’s ecosystem, eating insects and feeding wildlife.

American bullfrogs are an invasive species in California. State law requires markets to kill the bullfrogs when they are sold, although pet stores are allowed to sell them alive. Yet the bullfrogs make their way into rivers and lakes, where they spread the disease and devour everything from native tadpoles to ducklings.

Some of the bullfrogs that are free in the Bay Area are former pets. Buddhists may have released others during traditional ceremonies that liberate living creatures. Once in the environment, the frogs can reproduce.

Efforts to ban the live bullfrog imports have been strenuously opposed by Chinese-American leaders who defend their communities’ rights to a traditional part of their diet.

A study of 493 fresh-bought frogs from San Francisco, Los Angeles and New York found that 62 percent were infected with the chytrid fungus.

“We don’t know if the bullfrogs contributed to the introduction of B.d. into the U.S.,” said Lisa M. Schloegel, a disease ecologist and lead author of the study, which was published in the journal Biological Conservation in 2009. “But the bullfrogs are a constant source of infection.”

Vance T. Vredenburg, a biology professor at San Francisco State University who specializes in amphibians. said he had seen “literally hundreds, and tens of thousands” of dead animals on the shorelines of lakes. “With this fungus pathogen, we have something the world has never seen before,” he said. “It’s jumping from species to species to species, and we have very little predictability about what species it’s going to have an effect on.”

American bullfrogs survive the pathogen but can transfer the fungus spores to other, less fortunate species. The fungus has torn through the Sierra Nevada, leaving the once-abundant mountain yellow-legged frogs on the brink of extinction.

Proposals to ban the live imports into California were initially pushed forward by conservationists and animal rights groups in the mid-1990s. A few years later, scientists perplexed by worldwide amphibian deaths discovered B.d.

Assemblyman Paul Fong, Democrat of Cupertino, who championed a bill last year that outlawed the sale of shark fins, opposes a ban on live frog imports. So does Senator Leland Yee, Democrat of San Francisco.

“It’s a food stock that many Chinese-Americans rely on,” Mr. Yee said.

Pius Lee, chairman of the Chinatown Neighborhood Association in San Francisco, said he warned Buddhists that “pro-animal groups are watching you” and suggested they free animals from containers without releasing them into the wild.

But Kerry Kriger, an ecologist who founded the Santa Cruz-based nonprofit Save the Frogs after studying B.d. in Australia, said regulations were needed.

“People set them free on purpose. They escape, and the water they’re held in has chytrid in it — and that gets flushed out into the environment,” Dr. Kriger said. “You can ship in as much chytrid fungus into the United States as you want right now, and that’s what people do with the bullfrogs.”

Frog-killer disease was born in trade (Via Herp Digest)

Frog-killer disease was born in trade - The global amphibian trade spread the lethal chytrid fungus, which is decimating frogs around the planet, and it now looks like it may have created the disease in the first place.

November 7, 2011 by Michael Marshall, New Scientist

The team behind this finding are calling for an amphibian quarantine to help slow the disease's spread. Rhys Farrer of Imperial College London and colleagues sequenced the genomes of 20 samples of the offending fungus, Batrachochytrium dendrobatidis (Bd), collected in Europe, Africa, North and South America and Australia.

They found that 16 of the 20 samples were genetically identical, belonging to a single strain called BdGPL that had spread to all five continents. Tests on tadpoles also revealed that the strain was extremely virulent.

BdGPL's genome showed that it had formed when two strains mated, some time in the past 100 years. The best and simplest explanation is that 20th-century trade, which shipped amphibians all over the world, enabled the mating, says Farrer's supervisor Matthew Fisher.

"We've got to restrict trade, or at least make sure that amphibians are not contaminated," says Fisher.

One approach would be for countries to quarantine all imported amphibians and only allow them to stay if they are uninfected.

When it emerged that trade was spreading chytrid, the World Organisation for Animal Health made the disease notifiable, meaning that countries must report whether they have it or not. But that doesn't stop it spreading.

The two places in most urgent need of protection are Madagascar and south-east Asia, says Fisher: "They're the last redoubts of uninfected amphibian species." Both are hotspots of amphibian diversity, and are clear of BdGPL. Madagascar remains uninfected despite rampant BdGPL in Africa, and a recent survey shows that Asian chytrid strains are not very virulent (PLoS One, DOI: 10.1371/journal.pone.0023179).

If BdGPL reaches these places, it could quickly devastate their frogs. Within months of it reaching Montserrat, in the West Indies, in early 2009, conservationists had to fly giant ditch frogs - also known as mountain chickens - out of the country to save them from extinction.

Countries that already have BdGPL should also institute quarantine, says Peter Daszak, president of EcoHealth Alliance in New York. "This research shows that recombination can occur and give rise to new virulent strains," he says. "Blocking introduction of new strains will cut down on this."

Daszak adds: "It will be hard to stop the spread of new lineages of Bd, but if we look at the devastation that this pathogen has already caused, we desperately need to try."

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1111915108

Deadly Fungus Could Eat Up All The Bananas Before You Can Buy Them

The Beginning of the End for Bananas?

Already reeling from a 20-year losing battle with a devastating disease, the banana variety eaten in the United States is now threatened by a new—but old—enemy.
By Dan Koeppel

Our standard supermarket banana, a variety called Cavendish, may be at the brink of disaster. Chosen for its resistance to a fungal pathogen that wiped out its predecessor, the Gros Michel banana, the popular fruit has long battled a related fungus, which has all but devastated the banana industry in certain parts of the world. Now, it appears the Cavendish variety is facing a new threat—the very same fungal disease that drove Gros Michels off the market.


Cavendish bananas account for about 45 percent of the fruit’s global crop, with an annual export value of US$8.5 billion, according to the United Nations Food and Agriculture Organization. It was chosen to replace the original Gros Michel banana after a deadly fungal infection, known as Panama disease (Fusarium oxysporum f. sp. Cubense), wiped out much of the world’s banana crop in the first half of the 20th century.

Farmers adopted the Cavendish variety because it appeared to resist the blight, as well as about a dozen other banana diseases that also threaten the worldwide crop. But it wasn’t long before it too started suffering from disease. In the late 1980s, a mysterious malady began to wipe out Asian Cavendish plantations. Soil samples were sent to plant pathologist Randy Ploetz of the University of Florida’s Tropical Research and Education Center, who made the shocking identification: Panama disease was back, in the form of a new strain, which he dubbed Tropical Race 4.

Race 4 is just as virulent to Cavendish as Race 1 was to Gros Michel. The fungus enters the plant via its roots through infected soil or water and spreads via the plant’s vascular system. Once exposed, the plant yellows, and begins to look obviously sick—dried-out, sunken, and sagging. As the disease progresses, brown and purple stripes appear on the trunk, and the plant eventually dies. The disease, however, lives on, spreading via infected soil from plant to plant, plantation to plantation.

Today the disease has spread across Asia, into the Pacific, and to Australia, where it has devastated the island country’s banana industry. Though Race 4 has yet to hit Latin America, where bananas imported to the United States are grown, there’s little doubt it will, said Ploetz.

But it turns out that Race 4 is not the only threat to Cavendish bananas. As banana growers have fled from Race 4, replanting their Cavendish trees in areas only known to harbor Race 1, they quickly learned that Gros Michel’s old foe was now tormenting Cavendish bananas as well.


In 2010, scientists conducting a survey of plants infected in India, which grows and consumes more bananas than any other country in the world, were the first to conclusively identify the presence of Race 1 in the Cavendish banana. They published their findings in Plant Disease that November, and this March, Bioversity International—the global umbrella group for banana research—released a report confirming the finding: Race 1 had begun killing Cavendish plants in plantations around the Theni District of Tamil Nadu, India.

Banana scientists are still trying to determine why some Cavendish are no longer immune to Race 1. Altus Viljoenm, a researcher with the University of Stellenbosch in South Africa, speculates that this new strain of Race 1 may have evolved over time so that it could attack Cavendish.

Other researchers are skeptical of the finding. Ploetz notes that there have been rare cases in which Race 1 has killed individual Cavendish plants when they were already stressed—due to drought conditions, for example, or flooding. “I suspect that this is the same thing,” he said.

But the authors of the Plant Disease paper reported that they had confirmed the finding with laboratory tests on sterile, potted Cavendish. “To our knowledge,” the researchers wrote, “this is the first report of [such] a virulent strain.”

Today, there are no cures, treatments, or even reliable molecular diagnostic tests for either Race, partly due to lack of detailed information on the banana genome, according to Bioversity. Currently, the best available strategy is containment. Ploetz has developed a plan to fight Race 4 if it appears in Latin American plantations, involving the use of strict quarantines on affected plantations to prevent, at least temporarily, the spread of the disease.

But isolating infected plantations is more a stopgap than a solution, Ploetz knows. “It buys time,” he said, but barring any new discoveries, the spread of Panama disease remains inevitable. Ploetz said it’s important that similar agricultural practices be instituted in already affected countries to help prevent the spread to Latin America in the first place.

In the meantime, scientists are working to develop new approaches to quell disaster. Last year, for example, University of Queensland researcher James Dale began the first field tests of a genetically modified Cavendish, which he hopes will provide long-term resistance against Race 4.

Banana companies such as Chiquita and Dole are also reportedly working to develop new varieties. Though genetic modification has long been considered the only way to breed Cavendish, since the variety is completely sterile, recent research conducted in Honduras has revealed that a few Cavendish plants do produce viable seeds. Researchers at the Fundacíon Hondureña de Investigación Agrícola (FHIA) say these non-sterile fruit form the basis of a series of promising hybrids, that can be bred for resistance to the fungi. It will still be at least six years before the new breeds are ready to be brought to market, however, according to a source familiar with the project, or may never appear at all, now that the banana companies are no longer funding the research.


Most banana researchers agree that the real answer—as has been the case with crops like potatoes, apples, and grapes—is to abandon the monoculture that makes the emergence of a disease so devastating. A more diverse banana harvest would allow farmers to isolate susceptible bananas, surrounding them with more resistant varieties. If the solution ends up being a Cavendish stand-in that is resistant to both strains, on the other hand, the predicament of the banana monoculture—with its vulnerability to old, new, and yet-to-be discovered pathogens—would continue.

http://the-scientist.com/2011/07/22/the-beginning-of-the-end-for-bananas/