A 20-million-year-old flea entombed in amber with tiny bacteria attached to it provides what researchers believe may be the oldest evidence on Earth of a dreaded killer - an ancient strain of the bubonic plague.
If the fossil bacteria are related to plague bacteria, Yersinia pestis, the discovery would show that this scourge, which killed more than half the population of Europe in the 14th century, actually had been around for millions of years before that, travelled around much of the world, and predates the human race, researchers said.
It can't be determined with certainty that these bacteria, which were attached to the flea's proboscis in a dried droplet and compacted in its rectum, are related to Yersinia pestis, scientists said.
But their size, shape and characteristics are consistent with modern forms of those bacteria. They are a coccobacillus bacteria; they are seen in both rod and nearly spherical shapes; and are similar to those of Yersinia pestis.
Of the pathogenic bacteria transmitted by fleas today, only Yersinia has such shapes.
"Aside from physical characteristics of the fossil bacteria that are similar to plague bacteria, their location in the rectum of the flea is known to occur in modern plague bacteria," said George Poinar, an entomology researcher in the College of Science at Oregon State University.
"And in this fossil, the presence of similar bacteria in a dried droplet on the proboscis of the flea is consistent with the method of transmission of plague bacteria by modern fleas," he said.
These findings are in conflict with modern genomic studies indicating that the flea-plague-vertebrate cycle evolved only in the past 20,000 years, rather than 20 million.
Today there are several strains of Yersinia pestis, and there is evidence that past outbreaks of the disease were caused by different strains, some of which are extinct today.
While human strains of Yersinia could well have evolved some 10,000 to 20,000 years ago, Poinar said, ancient Yersinia strains that evolved as rodent parasites could have appeared long before humans existed. These ancient strains would certainly be extinct by now, he said.
"If this is an ancient strain of Yersinia, it would be extraordinary," Poinar said.
"It would show that plague is actually an ancient disease that no doubt was infecting and possibly causing some extinction of animals long before any humans existed," he said.
The fossil flea originated from amber mines in what is now the Dominican Republic, between Puerto Plata and Santiago.
Bubonic plague in modern times can infect and kill a wide range of animals, in addition to humans.
During the Middle Ages, however, three phases of the disease - bubonic, septicemic and pneumonic plague - earned a feared reputation.
Periodic waves of what was called the Black Death, for the gruesome condition in which it left its victims, swept through Europe and Asia, altogether killing an estimated 75 to 200 million people.
