Science: The Truth About... Ancient diseases

SOME OF the smallest life forms on the planet have caused some of the greatest carnage in human history. Until the latter half of the 20th century, however, our rather scanty knowledge of past scourges has come almost entirely from the written record - such as the Siege of Athens in 430BC, when a mysterious illness wiped out the besieged Athenians, and the Black Death which killed up to 50 million people in 14th-century Europe. With advances in genetic technology, however, science is able look afresh at ancient diseases in the hope of shedding new light on how they may come back to haunt us in the future.

The most famous example this century of the deadly power of infectious disease was in the aftermath of the First World War when a global pandemic of Spanish Flu is estimated to have killed 20 to 40 million people - a greater death toll than that from military action.

Many of those who escaped this flu outbreak succumbed to epidemic typhus, which is transmitted by a blood-sucking body louse. Typhus exploits the aftermath of war when the health and housing infrastructure collapses. Typhus killed a significant proportion of the 30 million people it affected after the First World War.

"Typhus ranks as one of the main epidemic diseases of human history, a truly apocalyptic pestilence that follows in the wake of wars and famine. Often typhus determined the outcome of military campaigns more effectively than the battles," said Michael Gray, a professor of biochemistry at Dalhousie University in Halifax, Nova Scotia. Professor Gray made the comments in Nature, which this month published the first full genetic analysis of the typhus bacteria, Rickettsia prowazekii. Knowing the genes of typhus will help scientists to design new drugs against the disease, he said.

Knowing the genetic structure of these viruses and microbes could also help scientists understand how they have evolved and how they may change in the future. Extracting the strain of flu which killed people in 1918 would provide a powerful insight into why it was so deadly. At least two teams of scientists are attempting this by analysing the lung tissue of frozen corpses of victims buried in Arctic permafrost.

Michel Drancourt, of the University of the Mediterranean in Marseille, has captured pieces of the plague bacterium, Yersinia pestis, from the dental pulp of skeleton recovered from a plague pit in southern France dating from the 16th to the 18th centuries. By examining the pulp of unerupted teeth, the researchers helped to ensure samples had not been contaminated by exposure to the environment. The analysis showed the DNA was similar to present-day plague genes and the next step is to see how the microbe has evolved over the intervening centuries.