More than 2,000 years ago, a plague gripped the Greek city of Athens. Ultimately, as much as a third of the population succumbed and the devastation, which helped Sparta gain the upper hand in the nearly 30-year-long war between the city-states. That much Thucydides--an ancient historian, general in the war and plague victim who recovered--conveys in his History of the Peloponnesian War. But he did not leave a precise enough description to decide definitively whether the disease was bubonic plague, smallpox or a host of other ailments. Now DNA collected from teeth in an ancient burial pit points to typhoid fever.

In 1994 researchers discovered a mass grave containing at least 150 bodies, including those of infants, deep beneath the Kerameikos cemetery in Athens. Contrary to Greek custom, the arrangement of the interred bodies grew progressively more haphazard as they were piled on top of one another and few burial offerings, which included a small number of vases, were left with the hastily buried corpses. Scientists dated the vases to roughly 430 B.C., which is coincident with Thucydides' report of when the plague broke out in the city.

Manolis Papagrigorakis and her colleagues at the University of Athens picked three random teeth samples from the plague victims and extracted the dental pulp. This soft core under the hard tooth covering can store pathogens and other information about the body for centuries. The researchers also tested two modern teeth to make sure that no false results were indicated.

Proceeding randomly through a list of possible causes, Papagrigorakis' team tested the pulp for the bacteria responsible for the bubonic plague, typhus, anthrax, tuberculosis, cowpox and catscratch disease before finding a match in Salmonella enterica serovar Typhi--the bacteria responsible for typhoid fever.

Typhoid fever--transmitted by contaminated food or water--causes fever, rash and diarrhea, all closely matching Thucydides' account of the terrible plague. The only thing that does not match up is the quick onset of the disease, because modern cases of typhoid fever typically take longer to gestate. "This inconsistency may be explained by a possible evolution of typhoid fever over time," Papagrigorakis writes in the paper published online in the International Journal of Infectious Diseases. "Considering the overcrowding and unsanitary conditions [especially regarding the water supply] within the walls of the besieged Athens, a typhoid epidemic would have been likely to break out."