Disease and Fleas: Ancient Flea Fossil Has Plague-Like Bacteria

A 20 million-year-old flea caught in amber with its bacteria has caught the attention of Oregon State University researcher George Poinar, Jr. and others.
That is, the bacteria on said flea has a strong resemblance in shape and form to the bubonic plague bacteria, Yersinia pestis, and researchers believe it may be Earth's oldest evidence of that historic killer, according to a release.

If the fossil bacteria are truly related to plague bacteria, this would show that the plague -- the one that killed more than half of 14th century Europe -- existed for millions of years before that period. Poinar published research on this in the Journal of Medical Entomology.

The ancient bacteria has similarities in size, characteristics and shape to modern forms of the plague bacteria. Both are coccobacillus bacteria; they both have rod and fairly round shapes. These days, Yersinia is the only flea-borne pathogenic bacteria that has these shapes, said a release.

"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," Poinar said in the release. "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."

The general genomic thought has been that the flea-borne plague cycle occurred only in the past 20,000 years. But today several Yersinia pestis strains exist and some strains that apparently (judging from evidence) caused outbreaks in the past no longer exist, according to a release.

It's possible, says Poinar, that the very oldest Yersinia strains arose as parasites on rodents, before humans existed. Those strains could also be extinct by now, said the release. 

"If this is an ancient strain of Yersinia, it would be extraordinary," Poinar said in the release. "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. Plague may have played a larger role in the past than we imagined."

The flea was found in amber mines in the current-day Dominican Republic, in what was in ancient times a tropical, damp forest, according to a release.

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