European Epidemic Disease in the Andes

The introduction of European epidemic diseases into the Andes, beginning in 1524 with the first epidemic of smallpox, was the single most important cause of mortality in the history of the Inca Empire and its successor states. Over the course of the sixteenth and seventeenth centuries, a series of epidemics — of smallpox, measles, influenza, typhus, and diphtheria — swept through the Andean populations, with a cumulative mortality that the historian Noble David Cook has estimated at about 86 percent of the central Andean population between 1520 and 1620. The indigenous Andean population, which had been largely isolated from the Eurasian disease pool for thousands of years, had no acquired immunity to these diseases, and the mortality was correspondingly high. The demographic collapse that resulted from the epidemics transformed the Andean world, reducing the labor force available for the Inca state and for the colonial economy, and creating a labor shortage that the Spanish attempted to address through the colonial mita and the importation of African slaves.

The disease pool of the colonial Andes

The Eurasian diseases

The diseases that were introduced into the Andes in the sixteenth century were all of Eurasian origin, and they had been endemic in Europe, Asia, and North Africa for many centuries. The most important of these diseases were smallpox, measles, influenza, typhus, and diphtheria. Smallpox, caused by the variola virus, was the most deadly of the diseases, with a mortality rate of perhaps 30 percent in unexposed populations. Measles, caused by the rubeola virus, was less deadly, with a mortality rate of perhaps 5 to 10 percent in unexposed populations, but it was highly contagious and spread rapidly. Influenza, caused by a variety of influenza viruses, was less deadly than smallpox or measles, but it was also highly contagious and could cause severe mortality in populations weakened by other diseases.

The other diseases that were introduced into the Andes included typhus, caused by Rickettsia prowazekii and transmitted by body lice, and diphtheria, caused by Corynebacterium diphtheriae and transmitted by respiratory droplets. The first documented epidemic of typhus in the Andes occurred in 1585, and the first documented epidemic of diphtheria occurred in 1614. Both diseases added to the demographic burden of the indigenous population, and both were especially deadly in highland populations that had been weakened by earlier epidemics. The cumulative effect of these diseases was, in effect, a demographic catastrophe that was unprecedented in the history of the Americas.

The Andean vulnerability

The Andean population was particularly vulnerable to European epidemic diseases for several reasons. First, the Andean population had been largely isolated from the Eurasian disease pool for thousands of years, and it had no acquired immunity to the diseases that the Spanish brought with them. Second, the Andean population was concentrated in densely settled highland basins, connected by the Qhapaq Ñan — the imperial road system — which allowed diseases to spread rapidly. Third, the Andean population was dependent on a complex agricultural system that required a large labor force, and the loss of labor to disease disrupted the agricultural system and led to famine. Fourth, the Andean population had a system of labor extraction — the mit’a — that required periodic gatherings of people, and these gatherings facilitated the spread of disease.

The Andean population was also vulnerable because of the limited medical resources available to it. The Inca had a system of samp’ay huasi — the houses of the healers — but the healers had no effective response to European epidemic diseases. The healers used herbal remedies and ritual practices, and they attempted to placate the huacas — the local sacred sites — but they had no understanding of the cause of the diseases and no effective treatment. The Spanish, who had brought with them the medical knowledge of early modern Europe, were unable to provide effective treatment for the diseases they had introduced, and the mortality was correspondingly high.

The first smallpox epidemic, 1524–1527

The arrival of the disease

The first European epidemic disease to reach the Andes was smallpox, which arrived on the Pacific coast in 1524 and spread along the Qhapaq Ñan into the interior of the continent. The disease, which was carried by Spanish expeditions from the Caribbean, reached the northern highlands of present-day Ecuador in 1524 or 1525, and from there spread south along the road system to the central highlands of Peru and to the basin of Lake Titicaca. The speed of the spread was increased by the Inca road system and by the system of labor extraction, and the disease reached the central Andes within a year or two of its arrival on the coast.

The first smallpox epidemic killed the Sapa Inca Huayna Capac and his designated heir Ninan Cuyochi, and it set off the civil war of succession between Huáscar and Atahualpa. The epidemic also killed a large proportion of the Inca nobility and a substantial fraction of the highland population, with mortality estimates ranging from 25 to 50 percent of the affected populations. The Spanish, who arrived in 1532, were able to exploit the disequilibrium created by the epidemic, and the capture of Atahualpa at Cajamarca in November 1532 was a direct consequence of the political instability that the epidemic had created.

The subsequent epidemics

Smallpox in 1529–1530 and beyond

The first smallpox epidemic of 1524–1527 was followed by a second epidemic, also of smallpox, which reached Peru in 1529 or 1530, and by a third epidemic, of measles, which arrived in 1531 or 1532. The second and third epidemics were less severe than the first, but they added to the demographic burden of the indigenous population, and they coincided with the Spanish conquest and the early years of the colonial regime. A fourth epidemic of smallpox occurred in 1558, and further epidemics of smallpox occurred in 1585 and again in 1595. The cumulative mortality from the smallpox epidemics, taken together, has been estimated at perhaps 50 to 60 percent of the central Andean population.

The smallpox epidemics were the most deadly of the European diseases, but they were not the only ones. An epidemic of measles, in 1531 or 1532, killed a substantial number of indigenous people, and further epidemics of measles occurred in 1558 and 1589. An epidemic of influenza, in 1558, killed a large number of indigenous people, particularly in the central highlands. An epidemic of typhus, in 1585, killed a large number of indigenous people in the southern highlands of Peru and Bolivia. An epidemic of diphtheria, in 1614, killed a large number of indigenous people in the central highlands.

The cumulative effect

The cumulative effect of the European epidemic diseases on the Andean population was catastrophic. The historian Noble David Cook has estimated that the total indigenous population of central Peru fell from about 9.5 million in 1520 to about 1.3 million in 1620, a loss of about 86 percent. The figures for Bolivia and Ecuador are of similar magnitude, and the figures for the highland populations are higher than the figures for the coastal and lowland populations. The demographic collapse was, in effect, the most important single fact about the conquest and its aftermath, and it has shaped the demographic structure of the Andean countries to the present day.

The demographic collapse had several important consequences. First, it reduced the labor force available for the colonial economy, and it forced the Spanish to develop a system of labor extraction — the colonial mita — that was more coercive than the Inca mit’a had been. Second, it reduced the indigenous population to a small fraction of its pre-conquest size, and it created a labor shortage that the Spanish attempted to address through the importation of African slaves. Third, it had important consequences for the indigenous cultures, since the loss of a large proportion of the population meant that many of the smaller indigenous languages disappeared, and the indigenous cultural traditions were maintained by a much smaller population.

The role of disease in the conquest

The weakening of the Inca state

The European epidemic diseases played a central role in the Spanish conquest of the Inca Empire. The first smallpox epidemic of 1524–1527 killed the Sapa Inca Huayna Capac and his designated heir, set off the civil war of succession, and reduced the population of the central Andes by a substantial proportion. The civil war, in turn, weakened the Inca state on the eve of the Spanish arrival, and the population loss reduced the labor force available for the Inca armies. The Spanish, who arrived in 1532, were able to exploit the disequilibrium created by the epidemic, and the capture of Atahualpa at Cajamarca in November 1532 was a direct consequence of the political instability that the epidemic had created.

The Spanish were aware of the role of the epidemic in the conquest. The Spanish chroniclers, including Francisco de Xerez and Pedro Sancho, recorded the indigenous accounts of the epidemic and recognized that the disease had weakened the Inca state. The Spanish also used the news of the epidemic to frighten the indigenous population, and they presented themselves as having a special relationship with the Christian God who, the indigenous peoples feared, had sent the disease. The question of why the Spanish were able to conquer such a large empire cannot be answered without taking the role of European epidemic disease into account.

The longer-term consequences

The European epidemic diseases had longer-term consequences for the Andean world. The demographic collapse of the Andean population reduced the labor force available for the colonial economy, and it created a labor shortage that the Spanish attempted to address through the colonial mita and the importation of African slaves. The demographic collapse also had consequences for the indigenous cultures, since the loss of a large proportion of the population meant that many of the smaller indigenous languages disappeared, and the indigenous cultural traditions were maintained by a much smaller population. The demographic collapse also had consequences for the indigenous religion, since the loss of a large proportion of the population meant that the religious specialists who maintained the traditional cults were no longer available, and the Spanish suppression of the Inti cult in the 1570s effectively dismantled the indigenous state religion in the highlands within two generations of the conquest.

The European epidemic diseases, in short, were the single most important cause of mortality in the history of the Inca Empire and its successor states. The cumulative mortality from the epidemics has been estimated at about 86 percent of the central Andean population between 1520 and 1620, and the demographic collapse that resulted from the epidemics transformed the Andean world in ways that the Spanish themselves could not have anticipated. The epidemics were, in effect, a demographic catastrophe that was unprecedented in the history of the Americas, and the consequences of the demographic collapse are still visible in the demographic structure of the modern Andean countries.