Breaking Down Science, Step by Step

What caused this Ancient Tuberculosis Outbreak?

Conventional wisdom dictates that when Columbus and other European explorers landed on the new world, they brought diseases such as Smallpox, Measles and Tuberculosis. So why does it look like Tuberculosis killed these ancient Peruvians ?

Sometimes, science really feels like detective work. We have our crime scene, which happens to be a region in Peru. Our victims were members of the Chiribaya culture, and they were killed sometime between AD 1028 - 1280. The good news is we have a prime suspect, the bad news is that the suspect seems to have a solid alibi. This is a conundrum that needs to be solved.


Shall we begin ?

The scene of the crime

The Chiribaya culture grew in the Osmore river basin in Peru. This civilization existed between 900-1350 AD, and lived before the Inca's, and long before Europeans arrived in the New World.

They were a simple people, who were divided amongst two ethnic groups. There were those who lived inland, cultivating crops and farming livestock like Alpacas and Llamas, and then there were other groups who hunted by the sea.

They get their name from their largest cemetery, found at Chiribaya Alta, in which 134 mummified remains were recovered, showing that both of these groups lived and traded with one another, sharing a culture even if they didn't share a lifestyle.


The great thing about mummified remains is that they preserve most of the soft tissue that usually rots away after death. So we can learn more about how these people lived, and more importantly, how they died.

The victims

14% of the Chiribayans showed some intriguing signs of disease.They show symptoms similar to the dead of other ancient coastal societies across Peru, and in societies further inland as well.


So let us go through the injuries.

The lungs of the victims some distinctive lesions around the alveoli, the tiny sacs that absorb oxygen from the air. As the alveoli died off, they formed into lesions, which spread further to cause damage to lymphatic vessels.


The bones of these victims also showed some damage too. People had lesions on their spines, on their skulls and their joints. at it's most extreme, there were signs that the damage had caused people's spines to collapse.

This evidence seemed to point in the direction of one culprit. Tuberculosis.


The suspect

Tuberculosis infects people through the lungs.when it reaches the alveoli, it hides inside white blood cells. A good hiding place as any, save for one side effect.Other white blood cells notice something is wrong, and attack it, and end up forming a cluster of cells called a granuloma.The cells at the centre of the granuloma begin to die off, releasing all sorts of nasty chemicals that kill of other cells, causing a lesion to develop. This lesion extends across the lymphatic highways that the white blood cells use to traverse the body. These lesions look similar to the ones observed in the lungs of our victims.


But what about the bone damage ?

A less well known after effect of Tuberculosis infection is "Pott's disease". This is where Tuberculosis travels to the spine, and the bones. When it sets up shop in these regions, it drives the immune system crazy once again, leading to the creation of lesions that cause damage to the underlying bone structure. This can lead to the spine curving into a hunched back, and lesions on the bones of victims. Which again, is similar to the disease that afflicted these ancient people.


The evidence is stark, Tuberculosis is guilty of this crime.

The alibi

The bacterium we are referring to as Tuberculosis is actually named Mycobacterium tuberculosis. It originated fairly early in human evolution, and whilst it was initially thought we acquired it from cows, more recent evidence suggests it was the other way around, so we actually don't know where it originally came from.


When humans began to travel across the globe, they took tuberculosis with them. As humans adapted and changed in response to their new environments, so too did the pathogens they carried.

The strains of Tuberculosis in Asia evolved and diversified, as did those in Africa and Europe. If you look at the genetic sequence of a strain of Tuberculosis, you can more or less guess, based on its ancestry, where it came from.


So if you were to look at cases of Tuberculosis in America, you would expect to see that they too had followed a different evolutionary past from their cousins in the Old World.

Instead, you tend to find that the strains of Tuberculosis endemic to the Americas are all descended from the European strains.


There can only be one explanation. Tuberculosis only came to the New World after the Europeans arrived, bringing all of their diseases with them.

All of these victims died long before the Europeans appeared on the scene. The evidence doesn't fit, so you must acquit !


New evidence

This mystery has persisted for many years, but recently, our technology has developed to a point where we can do something to ultimately settle this debate. We can now use fancy gene sequencers to finally identify the true perpetrator of these outbreaks.


Researchers took samples of bones and mummified tissues, and sequenced the genomes they found within them.

What they found may shock and amaze you. For the culprit behind these outbreaks was not Mycobacterium tuberculosis.


It was one of it's descendants, which jumped into another species of animal, the same way that Mycobacterium tuberculosis jumped into cows to become Mycobacterium bovis.

This bacterium was named Mycobacterium pinnipedii.

But even then, the question is how this strain managed to cross oceans to infect people on the peruvian coast, and the answer comes from the host of this organism.


The natural carriers of Mycobacterium pinnipedii are Seals and Sea Lions.


So they picked up the bacterium from people in the Old World. These seals would traverse the oceans, and settle on the beaches on the New World. Such as those off the coast of Peru.

The coastal peoples would hunt them, for food, and to craft their bones into tools.


In the process, Mycobacterium pinnipedii would infect them, and they would spread the disease to others. The people who hunted seals would trade their pelts, meat, and tools crafted from their bones with people further inland, and these goods carried the disease with them. It would eventually adapt to humans just as well as its ancestor, causing these ancient outbreaks.All of the evidence now points to this bacterium being the true culprit of this outbreak, and with that, I rest my case.


Pre-Columbian mycobacterial genomes reveal seals as a source of New World human tuberculosis


Image Credit

Peruvian Mummy, by Thomas Quine

Transmission electron micrograph of Mycobacterium tuberculosis, taken by Elizabeth "Libby" White as part of the CDC Public Health Image Library.


Southern Elephant Seal (Mirounga leonina) (young) in South Georgia by Serge Ouachée

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