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February 20, 2001

DNA Shows Malaria Helped Topple Rome


Noelle Soren
Scientists studying skeletons unearthed near Rome were able to recover DNA; from that, they deduced that an epidemic of malaria struck in the empire's waning days.

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Noelle Soren
Dr. David Soren, a classical archaeologist at the University of Arizona, led a team that excavated a cemetery north of Rome, where children were buried around the year 450.

An analysis of the bones of a child buried in a Roman cemetery more than 1,500 years ago has yielded what British and American researchers say is the earliest genetic evidence of malaria infection to be identified so far.

Traces of malaria had never before been identified definitively in such long-buried skeletons. The research encouraged some archaeologists to predict a wider and more productive alliance between biomolecular science and traditional excavation archaeology.

Archaeologists said that, in particular, the new findings provided strong support for the hypothesis that a widespread outbreak of an especially lethal form of malaria in the fifth century A.D. probably contributed to the decline of the Roman Empire. On the other hand, the epidemic may have saved Rome from a sacking at the hands of Attila the Hun, whose fear of the fevers may have caused him to turn back short of the city.

Until now, however, evidence linking the pestilence to malaria has mostly been from a few literary sources and indirect clues in a cemetery for infants uncovered at a villa near the town of Lugnano, 70 miles north of Rome. All the burials, some in mass graves, occurred over a brief period around the year 450. The presence of decapitated puppy skeletons, a raven's claw and other offerings of pagan ritual seemed to reflect the panic of an officially Christian people in the face of unsettling disease and death.

In the first successful application of new technology in finding traces of such ancient malaria infection, researchers at the University of Manchester Institute of Science and Technology in England were able to isolate minute samples of DNA from leg bones of a 3-year-old child. The DNA proved to be 98 percent identical to that in people infected with Plasmodium falciparum, the most virulent of the four species of human malaria.

Reporting on the tests in the current issue of the journal Ancient Biomolecules, Dr. Robert Sallares, a research fellow at Manchester, and Susan Comz, a student, said that two independent extractions and analyses produced similar results. "It is reasonable to conclude," they said, "that an infection with P. falciparum malaria was indeed the cause of death."

In a telephone interview, Dr. Sallares explained, "If there wasn't a vigorous infection at the time of death, I don't think we would have been able to find anything."

Of perhaps surpassing importance, the scientists said in their report, "These results confirm the utility of this method for detecting malaria DNA in human skeletal remains."

Dr. David Soren, a classical archaeologist at the University of Arizona in Tucson, praised the DNA results as "new and really exciting" because "the idea that this deadly type of malaria really existed in imperial Rome had never been documented."

An international team led by Dr. Soren excavated the children's cemetery in the early 1990's and discovered more than 50 small skeletons. Most, found in earthen jars, were the remains of stillbirths and early infant deaths. The falciparum parasite is known to cause miscarriage and infant death. A few older skeletons had porous and pitted cranium surfaces, which can result from an infectious disease like malaria.

This and considerable circumstantial evidence led Dr. Soren to the hypothesis that malaria epidemics might have had grave consequences on Rome. Scientists at the University of Rome have found evidence showing that falciparum malaria came from Africa, underwent mutations in Sardinia and was introduced in the marshy, mosquito-infested Tiber River basin by the fifth century.

Dr. Frank Romer, a Roman historian at Arizona, noted accounts of pestilence spreading through the countryside at this time and causing "sweats and chills," symptoms typical of malaria. It was in 452, a year or two after the infant burials, that Attila, marching toward Rome, suddenly decided against entering the city.

If the DNA tests have indeed linked the infant deaths to malaria and not some other causes, Dr. Soren said he hoped other archaeologists would take notice and begin to incorporate biomolecular research in their investigations.

"I think in 10 or 15 years, this will come to be standard practice in archaeology," he said. "We need not just excavate bones and throw them into a closet. We need to take these bones and make samples for DNA testing."

But Dr. Sallares sounded a note of caution. His laboratory in Manchester has wide experience using DNA analysis in examining human genetic mutations, crop genetics for studies in the history of agriculture and the family relationships of people buried in ancient Anglo-Saxon cemeteries. He is the author of "Malaria and Rome," being published this year by Oxford University Press.

In his journal article, Dr. Sallares said that "to unlock the full potential of biomolecular archaeology in relation to malaria and tackle all the fascinating problems" would require "much more work" developing reliable methods of analysis.

The analysis for the children's cemetery, for example, stretched current technology, Dr. Sallares said in the interview. The fragile bones of the youngest children were too degraded to produce useful samples; only those of a 3-year-old child, the oldest in the cemetery, yielded results. Pitting in its skull just above the eye sockets suggested that the child might have suffered malaria.

Pieces of a leg bone, considered more likely sites of bone marrow containing DNA traces, were ground to a powder. Then silica was added because it binds to DNA, if any remains. To isolate the DNA, researchers used a laboratory technique known as polymerase chain reaction, or P.C.R. Its ability to make something of almost nothing is one of the miracle advances of current genetic research.

By amplifying any residual DNA in a sample, making a million or more copies of a single molecule, P.C.R. enabled the scientists to detect and decode the imprint of malaria on the human genes.

All this took several months, Dr. Sallares said, and it has yet to be determined how widely the P.C.R. technique can be applied to the detection of other diseases or how far back in antiquity such investigations can yield results.

But when the scientists got a positive reading that the child in the Lugnano cemetery had an active malarial infection at the time of death, they repeated the tests to be sure this was no fluke. In December, Dr. Sallares was satisfied with the results of this unusual post-mortem examination, and he shared the good news with Dr. Soren.

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