Mexico: 500 years later, scientists discover what killed the Aztecs
In 1545 disaster
struck Mexico’s Aztec nation when people started coming down with high fevers,
headaches and bleeding from the eyes, mouth and nose. Death generally followed
in three or four days. Within five years as
many as 15 million people – an estimated 80% of the population – were wiped out
in an epidemic the locals named “cocoliztli”. The word means pestilence in the
Aztec Nahuatl language. Its cause, however, has been in questioned for nearly
500 years.
On Monday scientists
swept aside smallpox, measles, mumps, and influenza as likely suspects,
identifying a typhoid-like “enteric fever” for which they found DNA evidence on
the teeth of long-dead victims. “The 1545-50
cocoliztli was one of many epidemics to affect Mexico after the
arrival of Europeans, but was specifically the second of three epidemics that
were most devastating and led to the largest number of human losses,” said
Ashild Vagene of the University of Tuebingen in Germany. “The cause of this
epidemic has been debated for over a century by historians and now we are able
to provide direct evidence through the use of ancient DNA to contribute to a
longstanding historical question.”
Vagene co-authored a
study published in the science journal Nature Ecology and Evolution. The outbreak is
considered one of the deadliest epidemics in human history, approaching
the Black
Death bubonic plague that killed 25 million people in western Europe
in the 14th century – about half the regional population. European colonisers
spread disease as they ventured into the new world, bringing germs local
populations had never encountered and lacked immunity against.
The 1545 cocoliztli
pestilence in what is today Mexico and part of Guatemalacame just two
decades after a smallpox epidemic killed an estimated 5-8 million people in the
immediate wake of the Spanish arrival. A second outbreak from
1576 to 1578 killed half the remaining population. “In the cities and
large towns, big ditches were dug, and from morning to sunset the priests did
nothing else but carry the dead bodies and throw them into the ditches,” is how
Franciscan historian Fray Juan de Torquemada is cited as chronicling the
period. Even at the time,
physicians said the symptoms did not match those of better-known diseases such
as measles and malaria.
Scientists now say
they have probably unmasked the culprit. Analysing DNA extracted from 29
skeletons buried in a cocoliztli cemetery, they found traces of the salmonella
enterica bacterium, of the Paratyphi C variety. It is known to cause
enteric fever, of which typhoid is an example. The Mexican subtype rarely
causes human infection today. Many salmonella
strains spread via infected food or water, and may have travelled to Mexico
with domesticated animals brought by the Spanish, the research team said.
Salmonella enterica is
known to have been present in Europe in the middle ages. “We tested for all
bacterial pathogens and DNA viruses for which genomic data is available,” and
salmonella enterica was the only germ detected, said co-author Alexander
Herbig, also from Tuebingen University.
It is possible,
however, that some pathogens were either undetectable or completely unknown.“We
cannot say with certainty that S enterica was the cause of the cocoliztli
epidemic,” said team member Kirsten Bos. “We do believe that it should be
considered a strong candidate.”
