Key points
- Ancient DNA reveals 214 diseases over 37,000 years
- Plague emerged 6,000 years ago, affecting nomadic herders
- Understanding ancient diseases aids preparation for future pandemics
ISLAMABAD: To prepare for future pandemics, scientists are turning to history for insights. Over the past century, new pathogens such as HIV, Zika virus, and SARS-CoV-2 have caused global outbreaks. However, as researchers look further back in time, the historical record becomes less clear.
For example, Thucydides’ account of the plague of Athens around 430 BC, with its vivid descriptions of symptoms like bloody throats and foul breath, still leaves experts unsure about the exact disease responsible, according to The New York Times.
About thirty years ago, geneticists began examining ancient DNA to uncover clues about past diseases by analysing traces left in human skeletons. This research has recently accelerated. On Wednesday, a team of scientists revealed a comprehensive genetic timeline tracking the emergence of 214 diseases across Europe and Asia over the last 37,000 years.
Fascinating study
“The study is extensive, impressive, and overall quite fascinating,” said Hendrik Poinar, an ancient DNA expert at McMaster University in Canada, who was not involved in the research.
The researchers analysed remains from 1,313 ancient individuals, enabling them not only to identify the earliest known appearances of diseases but also to follow the waxing and waning of epidemics over centuries.
The oldest remains, belonging to hunter-gatherers, contained pathogens such as hepatitis B, the herpes virus, and the stomach bacterium Helicobacter pylori.
“As far back as we look, humans have been affected by infectious diseases,” explained Eske Willerslev, a geneticist at the University of Copenhagen and co-author of the study.
Notorious killers
Interestingly, these early remains showed no evidence of some notorious killers, such as Yersinia pestis, the bacterium that causes the plague. The researchers initially expected such diseases to emerge around 11,000 years ago, when humans began domesticating animals and thus increased their exposure to new infections.
However, the ancient DNA results contradicted this assumption. Plague and several other diseases appear to have jumped to humans much later, about 6,000 years ago.
Moreover, these pathogens did not initially infect early farmers but instead affected nomadic tribes in Russia and Asia, who began herding large livestock thousands of years after agriculture began.
The reason why these nomads, rather than farmers, were the first to be affected remains unclear. “We haven’t found a definitive explanation,” Dr Willerslev admitted.
Acquiring diseases
Martin Sikora, also of the University of Copenhagen, suggested that livestock herds might have acquired diseases from rodents and wild animals on the steppes, which then passed to humans.
Nomadic herders’ close contact with large herds could have made them particularly vulnerable. As these nomads expanded across the steppes of Asia and eastern Europe, their diseases flourished. Graves often contained several individuals infected with plague or other illnesses.
These epidemics were so severe that they shaped the nomads’ genetics. Last year, Dr Willerslev’s team discovered a surge in immune-related mutations that likely helped resist infections but may have also caused autoimmune diseases such as multiple sclerosis.
Lacking resistance
These diseases could have influenced Bronze Age history. The study suggests that nomads might have had an advantage over European farmers and hunter-gatherers, who lacked resistance to illnesses like plague and may have suffered massive population declines, facilitating the nomads’ expansion.
“This has played a major role in shaping the genetic landscape of today’s world,” Dr Willerslev said.
Some tracked diseases, like plague, are well known, but others are more obscure. For example, relapsing fever, spread by lice, surged 5,000 years ago in cycles of rise and fall, persisting to this day.
Dr Poinar noted that the factors behind such long-term fluctuations remain uncertain; epidemics might deplete susceptible populations before re-emerging, while pathogens evolve to better infect hosts.
Important start
While the study marks an important start, it has limitations. The DNA methods cannot detect RNA viruses like influenza or polio, and the data mostly covers Europe and neighbouring areas due to archaeological focus. “Africa would be fascinating to study, but data is scarce,” said Dr Sikora.
Understanding disease drivers over millennia could help prepare for future pandemics. Some pathogens that have thrived before may simply be waiting for their chance to return.
“If a disease has been successful in the past, it’s only a matter of time before it reappears,” concluded Dr Willerslev.
