An international team of researchers has completed the first major survey in Asia of a deadly fungus that has wiped out more than 200 species of amphibians worldwide. The massive survey could help scientists zero in on why the fungus has been unusually devastating in many parts of the globe -- and why Asian amphibians have so far been spared the same dramatic declines.
The disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis or Bd, is the culprit behind amphibian extinctions in Central, South and North America, Australia and Europe. The new Asian survey of the fungus, which was published Aug. 16 in the journal PLoS One, shows that Bd is prevalent at very low levels in the region.
Asia is home to a highly diverse set of amphibian species, and potentially could be vulnerable to Bd. But Vance Vredenburg, assistant professor of biology, said very little is known about the fungus and its impact on the health of amphibians in Asia.
"That's why we're excited about this first really big survey," said Vredenburg, who led the research team. "If you look at chytrid worldwide, Asia's been the black hole in our data."
From 2001 to 2009, Vredenburg and his colleagues surveyed more than 3,000 amphibians -- mostly frogs -- from 15 Asian countries, swabbing the toe webbing, thigh and abdomen of the animals to pick up any signs of Bd, which infects the skin of amphibians.
They found that the prevalence of Bd was very low throughout the region, appearing in only 2.35 percent of the frogs. The Philippines, Kyrgyzstan, Laos, Indonesia, Malaysia and South Korea were the only countries with any Bd infection.
The survey suggests that Bd is either emerging in Asia, or may have been in Asia at low levels for a long time or that some other factor is preventing Bd "from fully invading Asian amphibians," the researchers write.
Each site in the study was only surveyed once, Vredenburg explained, so it's difficult to determine whether Bd infections in the countries are newly expanding. It will be critical, he said, "to see how Bd prevalence is changing through time, because this is key to understanding the ultimate outcome of the disease."
If Bd has been in Asia for a long time, researchers would like to know why amphibians there have managed to co-exist with a fungus that has proved so destructive elsewhere. It is possible, for instance, that Asian amphibians might bear some sort of bacterial protection against Bd in their skins.
Other scientists are analyzing the genes of the Bd fungus collected globally, Vredenburg said, "to find out whether strains from different parts of the world also differ in their virulence."
Vredenburg said the possibility of another wave of extinctions highlights the need to follow the Asian survey with further research to answer all of these questions.
And if Asia is on the brink of a chytrid epidemic, Vredenburg and colleagues think it might start in the Philippines. "The prevalence and intensity of Bd infection is much higher here than anywhere else in Asia," he said. "Bd in the Philippines today looks similar to Bd in early outbreaks in California and South and Central America."
"This study is the first important step to understanding Bd in Asia," Vredenburg said. "It provides a solid foundation that future studies can build upon."
- Andrea Swei, Jodi J. L. Rowley, Dennis Rφdder, Mae L. L. Diesmos, Arvin C. Diesmos, Cheryl J. Briggs, Rafe Brown, Trung Tien Cao, Tina L. Cheng, Rebecca A. Chong, Ben Han, Jean-Marc Hero, Huy Duc Hoang, Mirza D. Kusrini, Duong Thi Thuy Le, Jimmy A. McGuire, Madhava Meegaskumbura, Mi-Sook Min, Daniel G. Mulcahy, Thy Neang, Somphouthone Phimmachak, Ding-Qi Rao, Natalie M. Reeder, Sean D. Schoville, Niane Sivongxay, Narin Srei, Matthias Stφck, Bryan L. Stuart, Lilia S. Torres, Dao Thi Anh Tran, Tate S. Tunstall, David Vieites, Vance T. Vredenburg. Is Chytridiomycosis an Emerging Infectious Disease in Asia? PLoS ONE, 2011; 6 (8): e23179 DOI: 10.1371/journal.pone.0023179
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