New Understanding of Ancient Origins of Tuberculosis May Help Find a Cure
New research published in the journal Nature Genetics has revealed that the origins of tuberculosis (TB) did not emerge around 10,000 years ago in animals and then pass to humans, as currently believed. Rather, the microbe that causes TB appears to have originated with early human ancestors some 70,000 years ago, before their apparent migration from Africa.
Throughout history, tuberculosis has been one of the deadliest infectious diseases of humankind. It reached its peak in the 19th and early 20th centuries as an endemic disease of the urban poor and was responsible for one in four deaths in England. Left untreated, TB will kill 50 per cent of the population it infects. Even today, 1 million to 2 million people die every year of TB, especially in developing countries. While scientists traditionally believed that Mycobacterium tuberculosis, the microbe that causes TB, emerged around 10,000 years ago in animals, and then passed to humans through the development of agriculture, a new study has found that TB’s link with humans runs much deeper: The bacteria actually originated with early human ancestors some 70,000 years ago.
The earliest detection of M. tuberculosis involved evidence of the disease in the remains of bison dated to approximately 17,000 years ago, while detection in humans came much later, around 4,000 BC, when traces of the disease were found in the spines of Egyptian mummies. This led scientists to conclude that the bacteria originated in animals and later passed to humans during the Neolithic Revolution when humans began domesticating animals.
Now, a team of international researchers led by Sebastien Gagneux of the Swiss Tropical and Public Health Institute has opposed these traditional findings, arguing instead that TB originated in the same place (Africa) but much earlier, and with early humans themselves, not with animals. Through detailed genetic analysis of 259 samples of TB bacteria collected from different parts of the world, they created a “family tree” of the microbe, marking its evolution throughout human history with the genetic mutations they observed. Their findings indicate that TB mycobacterium emerged some 70,000 years ago among humans in Africa. It then migrated with them, slowly spreading around the world as the population expanded.
The research also revealed that around 20,000 to 30,000 years ago, TB bacteria developed the ability to go dormant in its hosts, then re-emerge decades later. This ability may have developed as a survival strategy in the age of small, widely dispersed populations of hunter-gatherers, when TB might otherwise have killed off its isolated hosts quietly and died out itself, without gaining the opportunity to spread. This latency is what makes TB so hard to control, as the bacteria can hide out for extended periods among human hosts and break through in new environments.
Gagneaux and his team plan to use the genetic data gathered during their research to study the mechanism of the bacteria which causes it to either activate or deactivate. If they are able to unravel this mystery it may go a long way in helping to fight the disease and break its long, devastating pattern.