In 2018, a hundred years after the start of the worst pandemic in history, the Spanish Flu, numerous articles appeared marking the anniversary and asking whether the world is ready to fight another pandemic. This year, with the advent of the novel coronavirus and the respiratory disease that it causes, COVID-19, these questions are being answered, for better or for worse. Shortly after the spread of this coronavirus became known, a conspiracy theory arose from an infographic on social media that suggested the appearance of this pandemic fits a historical pattern. This meme pointed to the Spanish Flu a hundred years earlier, and cholera a hundred years before that, and finally, the bubonic plague a century prior to that. This claim that the appearance of pandemics fits a predictable pattern, and the concomitant implication that they may be planned or intentionally spread, is absurd. The meme cherry picks only the pandemics that fit its pattern, excluding, for example, SARS in 2003, HIV/AIDS beginning on the 1980s, and the Asian Flu of 1957-58 that claimed more than a million lives, not to mention any pandemic before the 18th century. Ridiculously, it places the bubonic plague in 1720, referring to an outbreak in Marseille, France that claimed 100,000 lives rather than the Black Death of the 14th century that claims as many as 50 million. Then there’s the fact that the years are all wrong, with the first cholera epidemic starting about 1817 and the Spanish Flu in 1918. In truth, since they were counting the Great Plague of Marseille, which was more of an epidemic than a pandemic, they might have been able to extend their false pattern back even earlier, to any major outbreak that occurred in any region about 20 years after the turn of a century. During the early 1600s and 1500s, there are no end of these to be found because of the Columbian Exchange, that rough intercourse of cultures, technologies, species, and diseases between the Old World and the New. For example, around 1620, a major outbreak of what was called “Indean Fever”—what today we recognize as Leptospirosis—killed an estimated 90% of coastal Native Americans on the east coast of North America, making colonial occupation far less complicated. And a hundred years before that, Cortés’s taking of the Aztec stronghold Tenochtitlan had been facilitated by an epidemic of smallpox that wiped out about 40% of their population. But these epidemics of 1520 and 1620 were not the only ones to appear with European invasion. Indeed, another, far deadlier disease would contribute to the collapse of the Aztec population about 25 years later, and as with COVID-19, there has been much speculation and disagreement about this disease’s nature and origin, debate which has lasted for centuries.

After the 1519 landing of the Spanish on mainland New Spain, or Mexico, the indigenous populations were decimated by an outbreak of smallpox that killed some 8 million. This disease was very familiar to the Spanish, and the reason why it had been previously unknown in the New World and spread so virulently is today well-understood. While at the time, smallpox was a disease transmitted from human to human, scientists believe that it originated as a zoonotic disease, that is, a disease transferred from animals to humans. This is, of course, something that is often brought up regarding the novel coronavirus, as it is believed to have been a zoonotic transmission from bats, which are known to act as reservoirs for more than one virus that may be transmitted to people, including the closely related SARS. Baseless conspiracy theories regarding the human engineering of the viruses notwithstanding, the consensus is that the current novel coronavirus was first transmitted to a person in the environs of a Chinese wet market, where live animals that would not normally be around each other are kept caged in close proximity to one another. Evidence points to the virus passing from bats to humans through some intermediate species like a civet or raccoon dog. Likewise, commonly known diseases spread to human beings in the distant past from animals, measles, for example, having first been a kind of canine distemper, and smallpox originally being a cowpox. The reason that diseases brought over to the New World spread so quickly and destructively was because the populations had never encountered them before due to the fact that the animal species that acted as a vector of contagion to humans simply didn’t exist in that part of the world. There had been no dogs there prior to the Columbian Exhange, and so no measles, no cows and so no smallpox. Likewise the leptospirosis that wiped out coastal Native Americans in the 17th century was spread by rat urine, most common species of rats being, once again, new to the shores of the Americas, introduced by Europeans, on whose ships the rodents had stowed away. When one considers the death toll that leptospirosis and even smallpox had on native peoples in the New World, however, the numbers are dwarfed by another plague, cocoliztli, which in 1545 decimated the Aztec population in Mexico, causing somewhere between 5 and 15 million deaths. Cocoliztli was long assumed to have been a zoonotic illness carried to the New World by the Spanish, but now we’re not so certain. Unlike smallpox, cocoliztli was not like anything Europeans had ever seen before, nor is it a disease we are more familiar with today. Thus, scientists and historians have been forced to dig for clues as to just what this devastating plague actually was.

Detail of a painting by Diego Rivera depicting the arrival of Cortez, via WIkimedia Commons

Contemporary Spanish accounts called it a great plague or epidemic, depending on the translation, but native writers used the Nahuatl word cocoloztli, meaning “pest” or “pestilence,” thereby giving it something of a biblical weight. And firsthand descriptions of its devastation certainly make it seem as if a god had smitten New Spain. From the onset of symptoms, the disease ran its course in only three or four days, usually concluding in the victim’s death. By the second or third day, it was said the sufferer often had a mental break, going sometimes entirely insane. According to the personal physician of King Philip II, Dr. Francisco Hernandez, it began with a fever and an insatiable thirst, after which the tongue would turn dry and grow dark. Next, the urine would grow dark, becoming green and sometimes even black. The patients’ pulse weakened, and they suffered a jaundice, their entire bodies and their eyes turning yellow. As neurological symptoms set in, including delirium, and even seizures, painful nodules emerged behind the patient’s ears, hard and full of fluid, and the patients complained of great pain in the abdomen and chest. Some kind of necrotic lesion then appeared around the mouth and genitals, like gangrenous ulcers. Dysentery was common, and by the end, copious amounts of blood poured from the sufferer’s anus, vagina, mouth, nose, and ears. Even talking about this gives me anxiety, like PTSD, having experienced sudden hemoptysis, or coughing up blood, during my bout with pneumonia a year and a half ago. It is terror-inducing, but perhaps, with any mercy, the sufferers of cocoliztli were already too delirious to feel this mortal fear. While Dr. Hernandez does mention some recoveries, for the most part, “Vital energy was consumed quickly.” A Franciscan historian named Juan de Torquemada called the pestilence “a great mortality” and described the results of a cocoliztli epidemic decades later, writing, “It was so big that it ruined and destroyed almost the entire land. The place we know as New Spain was left almost empty. It was a thing of great bewilderment to see the people die. Many were dead and others almost dead, and nobody had the health or strength to help the diseased or bury the dead. 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 without any of the solemnity usually reserved for the dead, because the time did not allow otherwise.”

In order to understand the true nature of this disease, we must first reconcile our primary source descriptions with our understanding of disease theory at the time in order to discern how trustworthy these reports may be. Based on Dr. Hernandez’s description of treatments that primarily focused on stopping the dysentery and attempting to stanch the bloody flux and letting the purulent fluid out of the nodules behind the ears, it may be that he and others dealing with this epidemic were still operating under the Hippocratic Theory of the Four Humors, which asserted that most disease was a result of an imbalance in bodily substances like phlegm, bile and blood, treatable by letting some of these humors out or preventing their loss in order to reimpose a balance. Hernandez indicates that when they managed to stop the prodigious blood flow from the nose, those patients were most likely to survive. However, he also states that some were allowed to bleed out, and that “the blood was expelled by some without severe disease,” so really, this appears to tell us nothing reliable. As for how the disease was spreading, the vector of transmission, as we’d called it today, it is discernible as well that doctors were laboring under incorrect notions. For almost two millennia, the miasmatic theory of disease had remained the consensus among healers and natural philosophers. This theory posited that diseases spread because of noxious emanations, or bad air, called miasmas, usually wafting from the rotting vegetation of some swamp or from the decomposing remains of some creature. These miasmas came to be known as “night air,” as it was believed that miasmatic emanations were more common after dark, prompting many to seek shelter indoors with their windows closed, when in fact, as we know now, sharing the stuffy air of an enclosed space with others, especially those who might be carrying an infectious illness, is far more likely to lead to the spread of diseases. Indeed, even the name of the disease malaria means “bad air.” Slowly, all the way through the 19th century, this came to be replaced by the contagion theory, that disease is spread through physical contact, and eventually with modern germ theory. However, even today, there remain some artifacts of this belief in our culture. Every time someone tells you that you’ll “catch your death” by being out in cold or wet weather, they are working under the same kind of misapprehensions as ancient quacks and sawbones. When Dr. Hernandez writes in his report that “[t]he weather was dry and quiet, and disturbed by earthquakes, the air was impure, filled with clouds but without resolving into rain,” he appears to have been suggesting a miasmatic vector of transmission. And his autopsies didn’t do anything to dissuade him of this. He noted “yellowish liquid” and bile as well as black blood, all of which was likely interpreted through the lens of the Four Humors theory, and he found the lungs in a state of putrefaction, which could have been attributed to the bad air of a miasma.

A historical depiction of miasmas spreading diseases, via Jezebel

Even the geographical spread of cocoliztli might have been seen as reinforcing the miasmatic theory. As Hernandez noted, the disease spread to a greater degree in the cold highlands, and less so in the lowlands, which could have been seen as some indication of bad airs circulating in that vicinity. However, there were other peculiarities of its spread that could not then be accounted for. For example, it appeared to infect and kill younger people at a great rate than older people, which seems counterintuitive. Hernandez also notes that the disease attacked regions where native populations lived more than others, only eventually attacking the Spaniards themselves. While Hernandez sees this in geographical terms, today we would understand it more in terms of the vulnerability of the native population. The fact that it ravaged one area more than others was simply because the oppressed natives were concentrated in that area, like a ghetto. At least one government official, Cristobal Godinez, acknowledged that the rampant spread of the disease among the natives may have had something to do with their treatment of them. “The reason so many Indians die of the pestilence is a God secret,” he says at first, hinting at likely pervasive beliefs that it may have been a divine punishment against them for their heathenism, but he quickly changes his tone. “I do not find any better answer than that in the past the Indians were not as badly mistreated and oppressed as they are today with heavy workloads. They are skinny and delicate, the disease finds them overworked and without resistance, so they are finished.” Certainly unhealthy living conditions and malnourishment could contribute to a disease’s spread, but with our current understanding of the indigenous peoples’ especial vulnerability to zoonotic diseases of the Old World, one might be tempted to suggest cocoliztli was also zoonotic and spread more widely among natives for this reason. Therefore, one of the first suspects was a hantavirus, commonly spread by rodents and their urine. However, the illness does not appear to have developed pulmonary symptoms, which would seem to rule out a so-called New World hantavirus. Another would be that it was an outbreak of the bubonic plague, which we know to have been associated with rats but borne by fleas, and cocoliztli victims’ high fever, low blood pressure, and sub-cutaneous nodules that appeared behind the ears, like the buboes of the plague, have all been interpreted as indications that this was the Black Death. However, the jaundice and the extreme bleeding from orifices do not appear to correspond with the bubonic plague. In fact, the profuse bleeding would seem to point to some kind of hemorrhagic fever.

Viral hemorrhagic fevers come in a variety of forms. Some forms have been known to originate from hantaviruses, spread by rodents, resulting in abdominal pain, fever, low blood pressure and bleeding, but as I said previously, a hantavirus seems unlikely based on the lack of pulmonary symptoms among cocoliztli patients. Hemorrhagic fevers can also develop from arenaviruses, another zoonotic virus with rodents as its natural reservoir. These fevers, like Lassa fever, typically come on more slowly, with death occurring within about 14 days of becoming symptomatic, a far longer duration than cocoliztli, which killed within days. In such hemorrhagic fevers, we see the same chest pain, diarrhea, low blood pressure, and bleeding from orifices, but we don’t see the jaundice or the nodules behind the ears. Then there are the hemorrhagic fevers caused by the filovirus, one example being Ebola, but again, the absence of one of Ebola’s tell-tale features, a rash on the upper arms and legs, seems to eliminate this as a candidate for cocoliztli as well. Finally, there are hemorrhagic fevers caused by the flavivirus, transmitted by mosquitoes, the most well-known being dengue fever and yellow fever. For a long time, in fact, yellow fever seemed to be the best explanation for cocoliztli, as it presents with sudden fever and body aches and concludes with jaundice and bleeding. Indeed, even the strange nodules behind the ear have been interpreted as the inflammation of the parotid salivary glands that is sometimes seen in severe cases related to yellow or dengue fever, and the unusual combination of a fever with a slow pulse is seen as a case of Faget’s sign, often seen in yellow fever and Typhoid fever. However, like leptospirosis, which was another possible candidate, yellow and dengue fever outbreaks in the Gulf of Mexico in the 17th century always spread in coastal regions, whereas cocoliztli ran rampant in the highlands. Moreover, physicians in the 17th century, who would have been familiar with cocoliztli, did not believe it the same as yellow fever, and during later outbreaks of cocoliztli, they did not think it to be yellow fever. And on and on it goes, through the lists of known diseases, always with some reason to cast doubt on cocoliztli being an identifiable disease. Bacteriologists have gone back and forth with numerous other illnesses, such as influenza, diphtheria, and pertussis, all of which were eliminated based on the descriptions of cocoliztli symptoms, especially because of the lack of respiratory complications. Perhaps the most debated was typhus, which even the Nobel prize winning French bacteriologist Charles Nicolle argued could have been the culprit. However, it has been convincingly argued that the Spanish physicians who described cocoliztli would have been familiar with typhus and therefore would have called it by its Old World name when writing about it. Additionally, as with Ebola, typhus’s tell-tale rash covering the entire body was conspicuously absent in the cocoliztli epidemic.

16th century Aztec drawing of smallpox victims, Wikimedia Commons

There has been much debate about whether typhus was an Old World import or existed already in the New World prior to European contact. One vector of typhus transmission is via lice, and it has been suggested that lice had been prevalent in Aztec culture long before the arrival of the Spanish. One story tells of an officer of Cortez seeing bags full of lice in the palace of Montezuma and learning that the poorest of the Aztecs would collect the insect to offer as tribute, since they had no wealth to offer. However, other scholars have suggested that these were not lice but rather cochineal insects, known for being used to produce a red dye, which the Spanish, being unfamiliar, mistook for lice. Nevertheless, it has been proven that North American flying squirrels are a reservoir of typhus, lending at least some credence to the notion that typhus was already in the New World. However, ignoring the inconsistencies, if cocoliztli were a typhoid fever outbreak endemic to Mexico, this offers no explanation for the selective immunity of the Spanish colonists, who one would assume, being new to that side of the world, would have fewer immunities to a strain of disease peculiar to that region. However, Rodolfo Acuna-Soto et al., in their 2002 article “Megadrought and Megadeath in 16th Century Mexico,” provide further reason for believing it to be an indigenous disease. First off, as indicated, the Europeans had never seen anything like it, which would seem to support the notion that they hadn’t brought it with them. Second, cocoliztli seems to have been mostly absent from the coastal plains, which goes against the pattern of Old World disease importations. Using dendrochronological or tree ring evidence, they proved that outbreaks of cocolioztli consistently occurred after periods of severe drought. Citing established outbreak dynamics, they reason that the virus spread among native rodent populations because of reduced resources and increased aggression, and thereafter spread to the native populations when infected rodents invaded homes and farms after the drought subsided. Thus, the highlands were more affected, being the agricultural region, and the over-worked and poorly-fed native population that cultivated the region to enrich their colonial rulers were the principal victims, being that it was they who came into contact with the rodents.

What remains would be to identify what virus the rodents were spreading. Still no single candidate seems to fit the description of cocoliztli’s symptoms. In 2018, a clue as to the identity of the real culprit was uncovered by a group of archaeologists and biologists who published the results of their study in Nature Ecology & Evolution. These researchers managed to find a plague cemetery in Mexico where victims of cocoliztli were buried. Taking the teeth of 11 people buried there and extracting DNA from the pulp protected by the enamel, they detected the presence of Salmonella enterica, known to cause paratyphoid fever, an enteric fever distinct from typhoid fever. They then confirmed their findings by comparing this with the DNA extracted from the teeth of persons buried in cemeteries known not to be in use during the epidemics, in which they found no salmonella. This, along with the fact that salmonella is known to proliferate among the poverty stricken living in crowded conditions, and the finding that people buried in the same plague cemetery whose graves indicated they had died before European contact had no sign of salmonella in their dental pulp, would seem to lay the blame for the collapse of the Aztec population once again squarely at the feet of the Spanish invaders. Paratyphoid fever would seem to explain a lot of cocoliztli symptoms, including fever, abdominal pain, slow heart rate, and diarrhea, and is even known to cause parotitis (or inflammation of the salivary glands) during the septicemic stage, accounting for the nodules behind the ear, as well as jaundice from deranged liver function and bleeding because of ulcers in the digestive system. However, these last three are not common, and the bleeding is usually internal, in the intestines, rather than expelled by the mouth and nose and ears. Therefore, there is still some question of whether a paratyphoid fever really provides a final explanation. One possible alternative explanation might be a mixed epidemic, that in the wet conditions following the end of a megadrought, circumstances aligned for a simultaneous outbreak of paratyphoid fever and some unidentified hemorrhagic fever. If that’s the case, though, and this was not one disease but rather a combination of them, it is surprising that this “perfect storm” recurred again and again over the next century.

The 16th-century population collapse in Mexico, as depicted in a figure published with the work of Acuna-Soto, et al. (public domain)

Could cocoliztli have been a disease that remains unknown to medical science today? If so, what are the chances that it could reappear? After killing millions and millions in 1545, cocoliztli showed up again in 1576 to wipe out half of the remaining population of indigenous peoples in Mexico. And beyond these two major outbreaks, there were eleven more, lasting throughout the first half of the 17th century. Today, as we fight this new form of coronavirus, we dread the idea of outbreaks of the disease COVID-19 recurring over and over in years to come, but history teaches us that we should expect it. And as all reasonable people have come to take this threat seriously, changing their daily routines and lifestyles drastically in order to make a difference and prevent worst case scenarios, it seems to me that it is also time for all of us to give more thought to how we might change our lives in order to fight the even greater threat to world health: global climate change. Not only does the future of our world look bleak in terms of more and more severe weather patterns, resulting in catastrophes like we’ve recently seen in California and Australian wildfires. It also portends an economic calamity, which it seems is one of the foremost concerns of those who would rather ignore the current health crisis. Economic collapse, of course, means poverty and famine. As we’ve seen in the story of cocoliztli, poverty and famine contribute to the spread of disease. And if that weren’t enough, the story of cocoliztli also shows us the direct link between climate and disease, with megadroughts contributing to the spread of zoonotic diseases. And if there is one thing we can expect far more of as global temperatures rise, it is drought, and with these climatic disruptions, disease. Listeners, I am sorry to be such a doomsayer here. To be clear, I am an optimist when it comes to the novel coronavirus. This is something we can weather, so to speak, and next year, with the production of a vaccine, something we can beat. But if we don’t put all of our considerable efforts into halting the bigger threat of global climate change, I see greater disaster on the horizon.

Cocoliztli: The Mystery Pestilence

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