Do No Harm

Riding evolution together: Humans and TB

This, then, is where it all began.

This, then, is where it all began.  


I could have been an anthropologist. In some sense, we all are: anthropologists. For what we do contributes towards a study of human kind, past and present. Or we kid ourselves into believing that what we do today is going to be a couple of odd shaped pieces in the jigsaw of tomorrow.

For some, it matters where we come from, even if it doesnt where we go. Especially when you hear stuff like the tuberculosis baccilus evolved just like human beings did.

Yes. Mycobacterium tuberculosis and human beings have more than co-habitation that binds them. An international group of researchers led by Sebastien Gagneux from the Swiss Tropical and Public Health Institute, has now identified the origin of the disease in time and space.

Using whole-genome sequencing of 259 Mycobacterium tuberculosis strains collected from different parts of the world, they determined the genetic pedigree of the deadly bug.. This genome comparison indicates that TB mycobacteria originated at least 70,000 years ago in Africa. Sounds familiar? The forerunner of the modern day human is said to have evolved from the Homo sapiens a few hundred thousand years ago, in the same continent: Africa. That's right, Myco's been following us for the last 70,000 years. Tenacious bug, as ever there was one.

Oh, and hold on. There's more from where that comes. The researchers compared the genetic evolutionary trees of mycobacteria and humans side-by-side. And to the researcher's surprise, these phylogenetic trees of humans and the TB bacteria showed a very close match. "The evolutionary path of humans and the TB bacteria shows striking similarities," Prof. Gagneux said, according to reportage by >Science Daily.

Essentially we originated in Africa, along with myco and made it out there, hand in hand, the bug growing with the bondage in virulence.

According to the Global Tuberculosis Report, 2012, the burden of TB remains enormous. In 2011, there were an estimated 8.7 million new cases of TB (13% co-infected with HIV) and 1.4 million people died from TB, including almost one million deaths among HIV-negative individuals and 4,30,000 among people who were HIV-positive. TB is also one of the top killers of women, with 3,00,000 deaths among HIV-negative women and 2,00,000 deaths among HIV-positive women in 2011.

"We see that the diversity of tuberculosis bacteria has increased markedly when human populations expanded," biologist Prof. Gagneux. Sure, the bug's been riding piggyback on humans for centuries, and gotten on remarkably well with a species known for its perfidy.

Human expansion in the so called Neolithic Demographic Transition period combined with new human lifestyles living in larger groups and in village-like structures may have created conditions for the efficient human-to-human transmission of the disease, he suggests. This may also have increased the virulence of the bacteria over time.

The results indicate further that TB is unlikely to have been a zoonotic disease - it has not jumped from domesticated animals to humans, as seen for other infectious diseases. "Simply, because Mycobacteria tuberculosis emerged long before humans started to domesticate animals," says Prof. Gagneux, on the Institute's website.

He also argues that digging up the gene path that Myco took, and tracing it back to it's origins serves a larger purpose. "The exploration of the evolutionary patterns of TB bacteria may help predicting the future patterns of the disease. This may contribute to future drug discovery and to the design of improved strategies for disease control." Any thing to check the onslaught of the ancient bacillus, especially with rising cases of drug resistant forms of TB: multi drug resistant and extremely drug resistant forms of tuberculosis.

Meanwhile, the jury's still out on which of the two species, that emerged out of Africa several thousands of years ago and evolved simultaneously, is deadlier: Mycobaterium tuberculosis, or Homo Sapiens.

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Printable version | Jan 26, 2020 1:49:41 AM |

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