Science News Roundup : 2018-01-19

Science News Roundup : 2018-01-19

Reading Time: 5 minutes

The dreaded Cocoliztli : The mysterious and deadly disease that wiped out the Aztecs

The Aztecs used to be masters of Mexico between 1300 and 1521. Then Cortes happened.

Aztecs Pyramid at St. Cecilia Acatitlan, Mexico State.

The Aztecs were an alliance of three tribes, the Mexnica1, the Texcoca2 and the Tepanoca. Their capital was at the great city of Tenochtitlan, and they spoke the Nahuatl language. Later, the Spaniards borrowed several Nahuatl words that eventually made their way into English, the great language sink. Examples include chile or chili, avocado, chocolate, coyote, peyote, guacamole, ocelot and mescal3.

When the Spanish conquistadors led by Hernan Cortes arrived in 1519, the Aztec empire was at its height of power, a formidable cultural, political, religious, social, commercial and military power in Mesoamerica. In two short years, the capital Tenochtitlan had fallen. The reason was smallpox.

Smallpox, a disease declared wiped out from the face of the Earth in 19804, was unknown in the New World before the Spaniards brought it from Europe. The Aztecs had no immunity against it, and fell like ninepins before it. In all, 5-8 million Aztecs perished in the 1520-21 epidemic. A second smallpox outbreak, the third epidemic, that began in 1576 killed millions more. But the deadliest epidemic was the second one. Occurring between 1545-50, this “huey cocoliztli” (or “great pestilence” in Nahuatl) killed somewhere from 5 to 15 million people between 1545 and 15505. For 500 years, no one was sure about the identity of the disease that caused “cocoliztli” 6 .

Until now. Probably7.

Ashild Vagene and coworkers have recently published a paper8 in Nature Ecology and Evolution in which they claim to have solved the 500-yr old mystery. According to Vagene et al, the Aztecs succumbed to a variant of paratyphoid, an enteric fever9 caused by the Salmonella enterica bacterium10. Symptoms of the disease included high fever, headaches, and bleeding from the nose, eyes, and mouth. Death usually occurred within four to five days of the onset of the disease. The disease spreads through water and food contaminated by infected fecal matter10.

MALT analysis of the DNA in the teeth enamel of the Aztecs. The presence of S. enterica is shown in red. Figure taken from original paper.

Vagene and coworkers collected and analyzed samples from the tooth enamel of unearthed skeletons belonging to victims who are believed to have succumbed to cocoliztli. It is suspected that the bacteria was probably brought over to Mexico via Spanish livestock and other domesticated animals. Whether this was accidental, or a part of a systematic biological warfare by the European invaders with the sole purpose to exterminating the Aztec population, is still an open debate.


Global map of antineutrino flux

Neutrinos are elusive elementary particles. They are very nearly massless, travel at very nearly c13, and very nearly do not interact with anything at all. That is why, though they are the second most common particles in the universe (photons being the most numerous, unsurprisingly), and nearly 600 trillion14 of them pass, every second, through a relatively unremarkable middle aged human male lying flat on the ground, they are very rarely detected. Neutrino detection has become a bit of a hot topic in experimental particle physics over the past century and a half. Experiments and observatories such as Super-Kamiokande in Japan, Daya Bay in China, CERN and Gran Sasso in Europe, and our very own INO have been instrumental in advancing neutrino physics.

About 99% of the neutrinos and antineutrinos15 on earth are geophysical in origin. They are created naturally through the decay of uranium and thorium in the Earth’s crust and mantle. The rest are anthropogenic; they are created within nuclear reactors.

Antineutrino flux on Earth’s surface. Red indicates high flux, while blue indicated lower flux.

Recently, a group of neutrino physicists and geophysicists have published the Antineutrino Global Map 2015 in the journal Nature Scientific Reports. There they plot antineutrino flux17 at the Earth’s surface. These antineutrinos are the anti-particles of the electron neutrino. There are of course two other types of neutrinos : muon neutrinos and tau neutrinos. Muons and tau leptons are cousins of the electron. The three types or “flavours” of leptons — electron, muon, and tau — all have charge -1 and spin 1/2. The mu lepton or the “muon” is about 210 times as massive as the electron, while the tau lepton (or taun, though I’m not sure if the terminology is standard) is almost 3500 times as massive as the electron18. The corresponding neutrinos have very small but non-zero mass18. These flavours are not fixed or permanent, and can oscillate among themselves19. Thus, a neutrino that was, at time 0 measured to have flavour electron, might, at a later time T, be measured to have flavour either muon or tau. This neutrino oscillation is a quantum mechanical phenomenon, and was the solution to the solar neutrino problem.

The map is conceptually a stack of six sub-maps, each of which is an “energy bin” that depicts a segment of the entire 0 MeV–11 MeV energy range the final image encompasses. (caption reproduced from original paper)

The muon neutrino was involved in a recent scientific controversy20. In September 2011, researchers at OPERA, a neutrino detection experiment in CERN, declared that they had observed muon neutrinos that were travelling at superluminal velocties, that is, faster than light. They confirmed their finding in a second attempt two months later. Einstein’s theory of relativity stipulates that the c, the speed of light in vacuum, is the fastest possible velocity in the universe. The OPERA experimental findings could conceivably prove this wrong. Six months later, in March 2012, ICARUS, another CERN neutrino detection experiment, published results that directly contradicted OPERA’s findings. In July 2012, OPERA declared that their results were erroneous, the fault being traced to faulty fibre optics. Which led to the conclusion that muon neutrinos never actually exceed c. Probably.

#ParticlePhysics #NeutrinoPhysics


The wonderful Academic Blogger Toolkit (by Derek Sifford) which I use to insert references has unexpectedly shorted out, resulting in some of the references flying off to the phantom zone. I hope to reinsert the references as soon as possible.

The people who probably gave Mexico its name.
The people who probably gave Texas its name.
Aztecs – Facts & Summary. (2009). Available at: (Accessed: 2018)
Smallpox. Wikipedia (2017). Available at: (Accessed: 2018)
What Killed the Aztecs? Maybe Not What You Think. Inverse (2018). Available at: (Accessed: 19th January 2018)
500 years later, scientists discover what probably killed the Aztecs. The Guardian (2018). Available at: (Accessed: 19th January 2018)
Berman, R. Salmonella May Be the Secret Behind the Demise of the Aztecs. Big Think (2018). Available at: (Accessed: 19th January 2018)
Vågene, Å. J. et al. Salmonella enterica genomes from victims of a major sixteenth-century epidemic in Mexico. N (2018). doi: 101038/s41559-017-0446-6
Typhoid, caused by Salmonella typhi, is also an enteric fever. .
Paratyphoid Fever. Wikipedia (2017). Available at: (Accessed: 2018)
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