The fall of the Aztecs tied to the Salmonella outbreak


2017-02-21 20:00:09




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The fall of the Aztecs tied to the Salmonella outbreak

The DNA of the bacteria by the age of 500 years was a direct reference to the epidemic — one of the deadliest for people — which broke out after the Spanish conquest. The study showed that one of the worst epidemics in human history, the plague of the sixteenth century which destroyed the native population of Mexico could have caused the deadly form of Salmonella from Europe.

In one study, scientists write that restored the DNA of intestinal bacteria from the burial sites in Mexico, associated with the epidemic of 1540 years that has ruined up to 80% of the indigenous population of the country. The findings of scientists were published on the bioRxiv server in the form of a Preprint.

This genetic evidence may be the first pointing to the pathogen, which led to the death of the Aztec civilization, says Hannes Schroeder, a researcher of ancient DNA in the natural history Museum of Denmark in Copenhagen, was not involved in the work. "This is a very cool study," he says.


the Corpses and gutters

In 1519, when the forces led by Spanish Conquistador Hernando cortés arrived in Mexico, the indigenous population was estimated at 25 million people. A century later, after the victory of the Spaniards and a series of epidemics, the number had decreased to 1 million.

The largest of these outbreaks was known as cocoliztli (from the word "Mor" in Nahuatl, the Aztec language). Two major cocoliztli occurred in 1545 and 1576 and destroyed from 7 to 18 million people living in the mountainous regions of Mexico.

"In towns and small and large, were dug large ditches, and from morning to sunset the priests just collected the bodies and dumped them in the ditch," noted Franciscan historian who witnessed the flash in 1576.

About the cause cocoliztli was little is known — offered options such as measles, smallpox and typhoid. In 2002, scientists from the National Autonomous University of Mexico (UNAM) in Mexico city proposed, as a variant of viral hemorrhagic fever, aggravated by the disastrous drought. They compared the amount of flash 1545 with the "black death" that raged in the fourteenth century in Europe.


Bacterial genomics

In an attempt to resolve this issue, scientists led by evolutionary geneticist Johannes Krause of the max Planck Institute in Jena, Germany, have extracted and sequenced DNA from the teeth of 29 people buried in a mountain of Oaxacan in southern Mexico. All but five were connected with cocoliztli, which, according to scientists, lasted from 1545 to 1550.

Ancient bacterial DNA from multiple people, consistent with the bacteria Salmonella (based on comparison with a database of more than 2,700 modern bacterial genomes).

Further sequencing of short, damaged fragments of DNA of these remains has allowed scientists to reconstruct two of the genome of strain Salmonella enterica, now known as paratyphoid C. Today, this bacterium causes typhoid fever, which manifests itself mostly in developing countries. If left untreated, 10-15% of infected people die. It is quite obvious why this bacterium could cause a pandemic, says Schroeder. It is suitable. But Maria Avila-Arcos, an evolutionary geneticist from the UNAM, does not think so. She noted that, according to some people, cocoliztli was caused by a virus, and the virus did not fit into methods of finding the first team.



The Proposal by Krause and his colleagues helped to conduct another study, which appeared on bioRxiv last week and added fuel to the fire of transfer of Salmonella paratyphoid With to Mexico from Europe.

A Team of scientists led by Mark Achtman, a microbiologist at the University of Warwick in Coventry, UK, were collected and sequenced the genome of the bacterial strain from the remains of a young woman buried around the year 1200 in Trondheim, Norway. This is the earliest evidence of the existence of the now-rare strain of Salmonella, proving that he was circulating through Europe. Both teams have so far refused to comment on their studies as they were presented in a peer-reviewed journal.

"actually, we wanted we to see both strains together," says Hendrik Poinar, an evolutionary biologist at McMaster University in Hamilton, Canada. And if I can get more ancient genomes in Europe and America, it will be possible to put an end to the question of whether deadly pathogen (e.g. Salmonella) to the New world from Europe.

The Existence of Salmonella paratyphoid With in Norway for 300 years before Mexico does not prove that the Europeans spread typhoid fever among indigenous Mexicans, says Schroeder, but this hypothesis has the right to life. A small percentage of people infected with Salmonella paratyphoid C, carries this bacterium, not falling sick, so it is healthy looking, the Spaniards could infect the Mexicans, who lacked natural resistance.

With Paratyphoid is transmitted through feces, and the collapse of public order during the Spanish conquest could lead to poor sanitary conditions, which were convenient for the Salmonella outbreak, say Krause and his colleagues.

A Study by Krause proposes a plan to identify pathogens in ancient hearths, says Schroeder. His own crew plans to search for ancient pathogens in the Caribbean places of burial that can be associated with catastrophic outbreaks were created after the arrival of Europeans.


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