The First Smallpox Epidemic in the Andes, 1524–1527

The first smallpox epidemic in the Andes occurred between 1524 and 1527, when the disease spread from the Caribbean coast into the interior of the continent along the imperial road system. The epidemic is the single most important epidemiological event in the pre-Columbian Andes, because it killed the Sapa Inca Huayna Capac and his designated heir, set off the civil war of succession between Huáscar and Atahualpa, and reduced the population of the central Andes by a substantial proportion. The epidemic preceded the arrival of the Spanish by about five years, and it prepared the way for the conquest in ways that the Spanish themselves recognized and exploited. The mortality from the epidemic, which is estimated to have been in the range of 25 to 50 percent of the affected populations, was the first of a series of European epidemics that, over the course of the sixteenth and seventeenth centuries, would reduce the indigenous population of the central Andes by about 86 percent.

Origin and spread of the epidemic

The Caribbean origin

The smallpox epidemic of 1524–1527 originated in the Caribbean, where the disease had been introduced from Europe in 1518 or 1519. The epidemic spread from Hispaniola to Puerto Rico and from there to Cuba, where it killed a large proportion of the indigenous population. From Cuba the disease was carried to the mainland by Spanish expeditions, and it reached the Pacific coast of present-day Colombia in about 1524. The first Spanish expeditions to the Pacific coast of South America — the second and third Pizarro expeditions of 1526 and 1531 — encountered the disease in northern Peru, and the Spanish accounts record that the disease had preceded them into the interior.

The epidemiology of the disease in the Andes is well established. Smallpox is caused by the variola virus, which is transmitted by respiratory droplets and which has a high mortality rate in populations without prior exposure. The Andean population had no acquired immunity to the disease, and the mortality was correspondingly high. The contemporary Spanish accounts, which include the chronicles of Pedro Cieza de León and Gonzalo Fernández de Oviedo, describe the disease in detail and report that it killed a high proportion of those infected. The indigenous accounts, recorded by the chroniclers Miguel Cabello Balboa and Titu Cusi Yupanqui, describe the disease as an unknown and terrifying affliction that produced pustules on the skin and that killed many of those who contracted it.

The spread along the Qhapaq Ñan

The epidemic spread along the Qhapaq Ñan, the imperial road system, and reached the central Andes in about 1524 or 1525. The road system, which ran from Quito in the north to Cusco in the south, allowed the disease to spread at a much faster rate than would have been possible in the absence of a major road network. The Spanish chroniclers report that the disease moved along the road at a rate of about 100 to 200 kilometers per month, and that it reached the central highlands of Peru within a year of its arrival on the coast. The disease also spread laterally, into the eastern lowlands and into the highland valleys that were connected to the main road by secondary roads, and it reached the basin of Lake Titicaca and the southern highlands of modern Bolivia by 1526 or 1527.

The speed of the spread of the disease was increased by the Inca system of labor extraction. The mit’a system, which required a portion of the labor of every household to be devoted to state purposes, brought large numbers of people into contact with one another, and the mitma system, which involved the forced resettlement of loyal subjects in recently conquered territories, created new routes for the spread of the disease. The Inca system of state granaries and storehouses, which required periodic gatherings of people for the redistribution of food, also contributed to the spread of the disease. The disease, in effect, was spread by the infrastructure of the Inca state itself, and the speed of the spread was a direct consequence of the centralization of the Inca state.

Impact on the Inca court

The death of Huayna Capac

The most famous casualty of the first smallpox epidemic was the Sapa Inca Huayna Capac, who died of the disease in about 1527, at the age of about fifty. The date of Huayna Capac’s death is given in the Spanish accounts and in the indigenous accounts, and it is generally accepted. The Spanish priest and chronicler Miguel Cabello Balboa, drawing on indigenous testimony, gave the year as 1527, and the date has been confirmed by the analysis of the Chinese and Spanish eclipse records. The location of Huayna Capac’s death is given as the northern city of Quito, in the highlands of present-day Ecuador, where the Sapa Inca had been campaigning in the years before his death.

Huayna Capac was not the only member of the Inca royal family to die of smallpox. His designated heir, Ninan Cuyochi, also died of the disease, and so did a great many members of the imperial household. The death of Huayna Capac and Ninan Cuyochi left the Inca state without a clear successor, and the dispute over the succession was the immediate cause of the civil war of succession between Huáscar and Atahualpa. The Spanish chroniclers report that Huayna Capac, on his deathbed, expressed a premonition that the death of so many of his family was the consequence of a new and terrible disease that had been brought from across the sea, and that he prophesied the arrival of a strange people who would overthrow the Inca state. The prophecy, which is recorded in several Spanish accounts, is almost certainly apocryphal, but it reflects the contemporary Spanish understanding of the role of the epidemic in the conquest.

The death of the Inca nobility

The smallpox epidemic killed a large proportion of the Inca nobility. The Inca had a system of royal panacas — the royal lineages descended from the previous Sapa Incas — and the panacas were the principal holders of the state land and the state storehouses. The epidemic killed many of the heads of the panacas and many of the principal officials of the Inca state, and the loss of the experienced administrators was a major blow to the Inca state’s capacity to govern. The epidemic also killed many of the quipucamayocs — the officials who kept the quipus — and the loss of the quipu-keepers made it difficult for the state to maintain its records and to communicate with its administrators in the provinces.

The impact of the epidemic on the Inca court was, in effect, a decapitation of the Inca state. The Sapa Inca, the designated heir, and a large proportion of the principal officials died within a year or two of one another, and the state was left in the hands of less experienced successors. The civil war of succession between Huáscar and Atahualpa was, in part, a consequence of this decapitation, and the Spanish conquest, when it came in 1532, was a conquest of a state that had been severely weakened by the epidemic.

The demographic impact

Mortality estimates

The mortality from the first smallpox epidemic is difficult to estimate, because the contemporary accounts are imprecise and the modern estimates vary widely. The Spanish chroniclers, who had no medical training and no demographic data, tended to exaggerate the mortality, and they reported that the disease killed a third, a half, or even two-thirds of the population. The modern estimates, which are based on the analysis of the population records of the colonial period, suggest that the mortality from the first epidemic was in the range of 25 to 50 percent of the affected populations, and that the total number of deaths in the central Andes was in the range of 2 to 4 million people.

The historian Noble David Cook, in his synthesis of the demographic evidence, has estimated that the total indigenous population of central Peru fell from about 9.5 million in 1520 to about 8 million in 1527, after the first epidemic, and to about 1.3 million in 1620, after a century of European rule. The first epidemic, in other words, was responsible for a population loss of about 15 to 20 percent, and the subsequent epidemics were responsible for the remainder. The first epidemic was, in effect, the opening event of a long process of demographic collapse that would transform the Andean world over the course of the sixteenth and seventeenth centuries.

The vulnerability of highland populations

The highland populations of the Andes were particularly vulnerable to the first smallpox epidemic. The highland climate, with its cold, dry winters and its cool, wet summers, was favorable to the spread of the disease, and the highland population was concentrated in densely settled basins that were connected by the road system. The highland populations were also vulnerable because of the limited medical resources available to them. The Inca had a system of samp’ay huasi — the houses of the healers — but the healers had no effective response to smallpox, and the disease spread rapidly through the highland communities.

The coastal populations of Peru were also affected by the first epidemic, but the coastal climate was less favorable to the spread of smallpox, and the coastal populations were less concentrated than the highland populations. The eastern lowland populations, which were connected to the highland road system only by secondary roads, were less affected by the first epidemic, but they were severely affected by subsequent epidemics, particularly the epidemics of measles and influenza in the second half of the sixteenth century. The differential vulnerability of the highland, coastal, and lowland populations is one of the most important features of the demographic history of the Andes, and it has shaped the distribution of the indigenous population in the modern Andean countries.

The role of the epidemic in the conquest

The weakening of the Inca state

The first smallpox epidemic of 1524–1527 was a major factor in the Spanish conquest of the Inca Empire. The epidemic killed the Sapa Inca Huayna Capac and his designated heir, set off the civil war of succession between Huáscar and Atahualpa, 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 the first smallpox epidemic into account.

The second and third epidemics

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 series of further epidemics — of influenza in 1558, of measles in 1589, of smallpox in 1585 and again in 1595, of typhus in 1585, and of diphtheria in 1614 — followed over the next century, with a cumulative mortality that has been estimated at about 86 percent of the central Andean population between 1520 and 1620.

The first smallpox epidemic, in short, was the opening event of a long process of demographic collapse that would transform the Andean world. The epidemic killed the Sapa Inca and his designated heir, set off the civil war of succession, and reduced the population of the central Andes by a substantial proportion. The Spanish, who arrived in 1532, were able to exploit the disequilibrium created by the epidemic, and the conquest of the Inca Empire was a direct consequence of the political and demographic crisis that the epidemic had created. The demographic collapse of the Andean population, in turn, was the most important single fact about the conquest and its aftermath.