Roughly one-third of the world's population carries the bacterium that causes tuberculosis. Although only approximately 10% of infected individuals will develop symptoms, they can be severe, including skeletal degeneration.
Many archaeologists belive that infectious diseases such as tuberculosis became established when people transitioned from a hunter-gatherer society to one based on permanent communities. This is a difficult hypothesis to test, because these people are long since dead.
An international team of scientists, led by Helen Donoghue at University College London (United Kingdom), has made an important contribution to this hypothesis. They have confirmed, on the molecular level, the presence of modern tuberculosis pathogens, in prehistoric humans, who lived roughly 9000 years ago.
The archaeological site.
The prehistoric site is known as Atlit-Yam; it is now submerged. It is several hundred meters offshore of modern-day Israel.
Carbon dating suggests that the site is between 8160 and 9250 years old. This was an established community, as suggested by the large quantity of human and non-human bones, plant remains, and tools at the site.
The site is well-preserved because it was covered in clay, sand, and salt water. Oxygen-deprived conditions such as these hinder decomposition by microbes.
Testing for tuberculosis.
There were lesions in the bones that suggest tuberculosis infection, but the diagnosis is not definitive. The scientists needed molecular confirmation. All analyses were performed by multiple scientists at multiple institutions in order to generate confidence in the results.
For this molecular confirmation, DNA and fat molecules were extracted from the ribs, arm bones (woman), and long bones (infant) of a 25-year-old woman and a one-year-old infant, both of whom were buried together. The DNA sequence of Mycobacterium tuberculosis, the bacterium that causes tuberculosis, is known, and is one identifying characteristic of the bacteria.
Fat molecules from Mycobacterium tuberculosis cell walls were also extracted from the skeletal remains. Fat molecules are more stable than DNA molecules, and have been used by other scientists to identify ancient pathogens.
DNA and fat molecules confirmed.
Five DNA fragments from Mycobacterium tuberculosis, the bacterium most likely to cause tuberculosis in modern times, were found in the skeletal remains. This DNA is identical to modern human Mycobacterium tuberculosis bacteria, not bovine tuberculin bacteria.
Additionally, fat molecules known as mycolic acids, from the cell wall of tuberculin bacteria, were extracted from the skeletal remains. Chromatographic analysis suggests that the composition is identical to that obtained from modern human Mycobacterium tuberculosis bacteria, not bovine tuberculin bacteria.
The origin of contagious disease in humans.
Archaeologists have historically believed that humans originally acquired tuberculosis from cattle. However, at this Atlit-Yam site, although extensive cattle bones were found, no Mycobacterium bovis DNA was detected.
This suggests that cattle played a more indirect role for the spread of tuberculosis, and other diseases, in early human populations. Cattle's contribution may have been through providing a steady source of food, enabing humans to live in larger, permanent groups, conducive to the maintenance and spread of diseases.
for more information:
Hershkovitz, I.; Donoghue, H. D.; Minnikin, D. E.; Besra, G. S.;
Lee, O. Y-C.; Gernaey, A. M.; Galili, E.; Eshed, V.; Greenblatt, C. L.;
Lemma, E.; Bar-Gal, G. K.; Spigelman, M.
Detection and molecular characterization of 9000-year-old
Mycobacterium tuberculosis from a Neolithic settlement
in the eastern Mediterranean.
PLoS ONE 2008, 3, e3426.