American Scientist

You're never too old, it seems, to benefit from molecular diagnosis. Over the past few years, some of the most modern techniques have been used to successfully diagnose diseases in the most ancient patients—mummies that are thousands of years old. The bones of these posthumous patients can now be analyzed by the tools of modern imaging, and DNA remaining in their tissues can be extracted and analyzed. Mummified remains can be probed by a CAT scan, and the scant remaining DNA of pathogens that once afflicted them can now be amplified by the polymerase chain reaction (PCR) and identified.

Granted, the diagnoses may be a little too late to help these people, but the new medical information is a boon to anthropologists looking for a more complete picture of life in ancient times, contact between populations and maybe even the very origins of infectious diseases. University of New Mexico anthropologist Jane Buikstra writes in a recent review that the application of molecular PCR to the study of ancient diseases constitutes "the most spectacular methodological advance" to these endeavors in recent times.

In some cases, the story emerging from disease analyses contradicts the image that people left of themselves. For example, anthropologists now believe that life in ancient Egypt was not as ideal as one might believe from artifacts of the period. "We've suspected that much of the ancient literature painted a rosy picture," says Rosalie David, director of the Egyptian Mummy Research Project at the Manchester University Museum in Manchester, England. "Many of the paintings of the time show people who are young and beautiful, because this is how they wanted to be seen in the next life."

Their remains tell a different story. Looking at DNA and other medical evidence is, says David, "as important as literature and art, because it provides hard evidence."

The hard evidence found by David and other anthropologists suggests that the ancient Egyptians suffered from a large number of diseases. Most of these were caused by parasites, but recently a group of German scientists provided definitive molecular evidence of an infectious disease in an approximately 3,000-year-old mummy from Thebes.

Pathologist Andreas Nerlich and colleagues in the departments of pathology, anthropology and radiology at Ludwig Maximilian University in Munich found that a DNA fragment in the mummy's lung came from Mycobacterium tuberculosis, the organism that causes tuberculosis. In order to make the diagnosis, the team, who described their work in the November 8, 1997, issue of the British medical journal The Lancet, employed PCR to augment the small amount of M. tuberculosis DNA they extracted from the mummy's lung tissue. The authors note that this is the first report of such an analysis in an Egyptian mummy, and only the second time tuberculosis DNA has been extracted from any mummy. Molecular extractions, notes Buikstra, are important because they "finally settle the issue of the nature of the disease we had been seeing in skeletal remains."

Indeed, for many decades anthropologists studying disease in both the Old and New Worlds have found deformities in mummy skeletons that suggest, but do not prove, that tuberculosis might have afflicted ancient people. The difficulty, notes Buikstra, is that many other diseases also deform the skeleton. Barring any contamination, she notes, the DNA findings are definitive.

With an unequivocal diagnosis of tuberculosis, she notes, anthropologists can now "move on to some of the more interesting questions." Among those questions, says Buikstra, is how the disease arose in the first place. In 1994 a team that included Buikstra, then at the University of Chicago, along with Wilmar Salo, Arthur Aufderheide and Todd Holcomb of the University of Minnesota at Duluth, became the first group to extract tuberculosis DNA from any historical specimen. In their case, the specimen was a 1,000-year-old mummy from Peru. The mummy's age, notes Buikstra, is significant because it predates the arrival of Christopher Columbus to the New World—the first contact the aboriginal peoples of the Americas would likely have had with Old World pathogens. Based on these findings, Buikstra suggests it is likely that tuberculosis in the New World arose independently and prior to contact with Old-World disease.

But if the disease was not passed on from other people, where did it come from originally? Here Buikstra suggests that disease in the Americas originated as an animal pathogen. Further DNA analysis might someday indicate whether the disease afflicting people originated in bovids or mice, or maybe even llamas or guinea pigs. In addition, the information would tell something of the state of animal husbandry at the time, she says.

DNA analysis of ancient people is just in its infancy, says David. In addition to determining the presence of other infectious diseases, comparisons of ancient pathogens with their modern counterparts may reveal the evolution of a pathogen over time. Other studies are planned to trace the spread of pathogens through and between various populations. David herself is now involved in a study that seeks to explore the epidemiology of the parasitic disease schistosomiasis in Egypt over the past 5,000 years, including its patterns in modern Egyptian populations, where it is estimated that about 20 percent of the population is infected with the parasite. David is part of a consortium that is developing a bank of ancient Egyptian tissues that she and colleagues will analyze using modern DNA extraction and sequencing techniques as well as highly sensitive immunological analyses.

David acknowledges the irony of treating these most ancient human remains with the most up-to-date medical advances, but adds that the ancient Egyptians would have been pleased. "They wanted eternity, and they certainly seem to have got it."—Michelle Hoffman