Applying a bit of detective work to centuries-old dental pulp, researchers have captured an actual piece of antique Yersinia pestis--the bacterium that causes the plague. The work, which uses DNA-detection techniques, confirms that the disease was responsible for epidemics centuries ago in southern France.
Until now, historians and scientists studying ancient plagues have relied on symptoms recorded by contemporary observers. But a team of researchers led by Michel Drancourt at the Université de la Mediterranée in Marseille reasoned that dental pulp, which is both durable and likely to harbor infection, would be a good place to find intact DNA evidence. After locating two mass burial sites for plague victims dating from the 16th and 18th centuries, the scientists removed a dozen teeth from five skeletons. They also took seven teeth from corpses buried elsewhere that showed no obvious signs of the disease. By using only pulp from unerupted teeth, which were surrounded by jawbone, the researchers helped ensure that their samples hadn't been contaminated from subsequent contact by microbial DNA.
DNA amplification showed nucleotide sequences in the plague victims' pulp that matched segments in the modern plague strain, which infects 1000 to 2000 people worldwide every year. The seven nonplague teeth yielded no trace of the deadly sequences, the researchers report in the 13 October Proceedings of the National Academy of Sciences.
The work "paves the way for us to look at past epidemics at a molecular level," says George Sensabaugh, a professor of biomedical and forensic sciences at the University of California, Berkeley. The next step, he says, is to show how Y. pestis strains have evolved by uncovering infected teeth from other eras and regions.
