A killer¹ has been caught in the act（当场） : the first before-and-after view of an infectious disease that led to an amphibian²（两栖类的） die-off has been released by the scientists who tracked it. The results are published this week in the journal Proceedings³ of the National Academy of Sciences (PNAS).

Like a wave, incidence of the fungal（真菌的） disease that wipes out Central American frogs--chytridiomycosis--advances through the region's highlands at a rate of about 30 kilometers per year.

After the disappearance⁴ of Costa Rica's golden frogs in the 1980s, Karen Lips, a biologist at the University of Maryland, established a monitoring program at untouched（未受影响的，未改变的） sites in neighboring Panama.

Of the 63 species she identified during surveys conducted from 1998 to 2004 in Omar Torrijos National Park, located in El Copé, Panama, 25 species disappeared from the site in a subsequent epidemic⁵.

As of 2008, none of these species had reappeared.

Were there additional species in the park not previously⁶ known to science?

To find out, the authors used a genetic⁷ technique called DNA⁸ barcoding to estimate that another 11 unnamed or "candidate" species were also present.

Combining field research（实地调查研究） and genetic information, the authors discovered that five of these unnamed species were also wiped out.

"Frog and salamander（火蜥蜴） extinction⁹ due to the chytrid fungus¹⁰（壶菌） is increasing worldwide," says Sam Scheiner, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research.

"These methods will allow a rapid measure of their diversity, so that we can monitor, and possibly mitigate¹¹（减轻，缓和） , that extinction."

"It's sadly ironic¹² that we are discovering new species nearly as fast as we're losing them," says Andrew Crawford, former postdoctoral fellow at the Smithsonian Tropical Research Institute (STRI) and member of the Círculo Herpetológico de Panamá, now at the University of the Andes in Colombia.

"Our DNA barcode（条形码） data reveal new species even at this relatively¹³ well-studied site, yet the field sampling shows that many of these species new to science are already gone."

An epidemic that wipes out a whole group of organisms is like the fire that burned the famous library of Alexandria, the scientists say.

It destroys a huge amount of accumulated information about how life has coped with change in the past.

Species surveys are like counting the number of different titles in the library; a genetic survey is like counting the number of different words.

"When you lose the words, you lose the potential to make new books," says Lips.

"It's similar to the extinction of the dinosaurs¹⁴. The areas where the disease has passed through are like graveyards¹⁵. There's a void to be filled--and we don't know what will happen."

"This is the first time that we've used genetic barcodes--DNA sequences unique to each living organism--to characterize an entire amphibian（两栖类的） community," said Eldredge Bermingham, STRI director and a co-author of the paper.

"The before-and-after approach we took with these frogs tells us exactly what was lost to this deadly disease--33 percent of their evolutionary¹⁶ history."