Cocoliztli, a Nahuatl word meaning pestilence or sickness, describes a series of catastrophic epidemics that struck Mexico during the 16th century. This devastating illness is recognized as one of the deadliest epidemics in human history, leading to an immense collapse in the native population. Its historical impact reshaped the demographic landscape of post-conquest Mesoamerica.
The Cocoliztli Epidemics in 16th-Century Mexico
The 16th century in Mexico witnessed a profound demographic catastrophe, largely attributed to the cocoliztli epidemics. Two major outbreaks caused widespread mortality, severely impacting the indigenous population in the wake of the Spanish conquest.
The first major cocoliztli epidemic occurred between 1545 and 1548, resulting in an estimated 5 to 15 million deaths. This initial wave alone eradicated up to 80% of the native population.
A second significant outbreak followed from 1576 to 1581, claiming an additional 2 to 2.5 million lives. This epidemic reduced the remaining indigenous population by approximately 50%. Combined, these two major cocoliztli events are thought to have caused between 7 and 17.5 million deaths, fundamentally altering the societal structure of New Spain.
Symptoms and Historical Accounts
Descriptions of cocoliztli’s clinical presentation come from 16th-century indigenous and Spanish chroniclers, notably physician Francisco Hernández de Toledo. He documented a range of severe symptoms during the 1576 outbreak. Those afflicted experienced high fever, intense headaches, and vertigo.
Other observed signs included a black tongue, dark urine, and the presence of large nodules behind the ears, which sometimes extended to the neck and face. Profuse bleeding from the nose, mouth, and eyes was also a common and distressing symptom. Patients often developed dysentery, severe abdominal and chest pain, and some exhibited neurological disorders and jaundice. Death frequently occurred rapidly, often within three to four days of symptom onset.
These detailed historical accounts were particularly informative for later researchers because the reported symptoms did not precisely align with those of known European diseases like smallpox, measles, or typhus. This distinct clinical picture differentiated cocoliztli from other epidemics of the period.
The Scientific Search for the Pathogen
Modern scientific investigation has shed light on the likely causative agent of the cocoliztli epidemics. A breakthrough came through the application of advanced paleogenomics, a technique that allows for the extraction and analysis of ancient DNA. Researchers examined DNA samples from the teeth of 29 individuals buried in a cocoliztli-era cemetery at Teposcolula-Yucundaa in Oaxaca, southern Mexico.
From 10 of these individuals, scientists successfully identified genetic material belonging to Salmonella enterica subspecies enterica serovar Paratyphi C. This specific bacterium is known to cause enteric fever, a disease type that includes typhoid and paratyphoid fevers.
The identification of Salmonella enterica Paratyphi C from these ancient remains provides compelling molecular evidence for its role in the 1545 cocoliztli outbreak. While researchers acknowledge that other pathogens might have circulated, the presence of this specific bacterial strain aligns with many of the severe symptoms recorded in historical accounts.
Environmental Factors and Disease Spread
Environmental conditions played a significant role in triggering and exacerbating the cocoliztli epidemics. Paleo-climatological evidence, including tree-ring data, indicates that the major outbreaks coincided with one of the most severe and prolonged megadroughts in North American history. This drought extended across vast regions, from Mexico to Canada, during the mid-16th century.
Extreme drought conditions would have severely limited access to clean water sources. As water supplies dwindled, contamination with Salmonella bacteria from human or animal waste would have become more concentrated. The crowded living conditions in post-conquest settlements further facilitated the spread of the pathogen.
The prolonged drought also led to widespread famine and malnutrition among the indigenous population. A weakened immune system, resulting from inadequate food and water, would have made individuals far more susceptible to severe illness and death from the Salmonella infection. This combination of environmental stress and concentrated pathogen exposure was catastrophic for 16th-century Mexico.