Environment Latin America

Epidemics in the Conquest of Latin America

Smallpox epidemic in the 16th century Florentine Codex.

By Viviana Espinosa Moreno, BA

The mass movement of people not only implies the mobilization of goods, culture, beliefs, and technology. Other agents can be relevant when we study the impact of such movements in host societies. Especially in exploring diseases and epidemics the agency of certain non-human elements like animals, plants, or microorganisms are pivotal to understand the history of some peoples and moreover to highlight the relationship between nature and society or diseases and society.

A demographic disaster

One of the historical events that elucidate this relationship is the conquest of America. It is recorded that more than half of the original indigenous population disappeared due to about 20 epidemics that were introduced within the 16th and 18th centuries. A more recent update estimated that an initial population of 54 million (similar to our 60.5 million) was reduced to 5.6 million, thus a 90% decline (Koch et al., 2018).

One of the theories that explain this demographic disaster is according to Crosby (1976) what he calls the “virgin soil epidemic” defining it as “those in which the populations at risk have had no previous contact with the diseases that strike them and are therefore immunologically almost defenseless.” In his point of view, this explains to some extent the success of the colonization project over the native populations.

However, we also must take into account other factors that created an ideal environment for diseases to spread, having a deadly effect on indigenous peoples. One example were the poor working conditions in the forced labor systems such as “Encomiendas and Mitas,” which deteriorated the physical health of indigenous peoples. These conditions increased the likelihood to die of any diseases. Accordingly, changes in the economic and social structures among the indigenous communities made them more vulnerable and defenceless to these factors.


Influenza was one of the first diseases that traveled with the Spanish in the era of Columbus. The Spanish veterinarian parasitologist and historian, Miguel Cordero del Campillo, showed in his work, “Crónica de Indias” that the first epidemic of European origin that reached America was the flu, which appeared to have had a zoonotic nature. The horses and pigs that Columbus embarked on the Canary Islands on his second trip to America fell ill from a respiratory illness identifiable with influenza, which also affected some crew members. This included Columbus himself, according to various chroniclers (Cordero del Campillo, 2001). There is evidence that the disease appeared the day after the disembarkation and subsequently spread on the island of what is today the Dominican Republic. There, it affected the Taíno community with particular intensity. Fray Bartolomé de las Casas, recounts how “people began to fall ill […] with terrible fever.” Another chronicler, Fernández de Oviedo, reports that: “more than two parts or half of the Spaniards died, and of the Indians themselves so many died that they could not be counted” (De Las Casas, 1877)


Another epidemic that contributed to the demographic catastrophe of Pre-Hispanic America was smallpox, the most contagious and deadly of the epidemics in America. In Puerto Rico, the first case of smallpox was documented in 1518, apparently first transmitted by an African slave, who came from one of the slave ships that arrived on the island. In Mexico, according to the chronicles, smallpox was also introduced in 1520 by a black slave, Francisco Eguía, who arrived with an expedition led by Spanish conquistador Pánfilo Narváez (147?–1528). (McCaa 1994). The disease first spread through Veracruz, then later extended to Tlaxcala, until reaching Tenochtitlan in the same year. In Tenochtitlan, one of the most densely populated cities of its time, smallpox spread with such force and speed that it contributed to the fall of the city.

A large part of Mexico’s indigenous population disappeared in the 16th century. Today’s specialists agree that the mortality of the smallpox epidemics of 1520, 1545, and 1576 could have been close to 80%. To give some numbers on the magnitude of the tragedy, McNeill, in his book “Plagues and People” (1977), calculates that in Mexico, of the 25 million people who may have existed shortly before the arrival of the Spanish, by the year 1620 only about 1.6 million remained. The smallpox disease even spread from Central America through Panama to the Andes and reached the Inca Empire before the arrival of another conquistador, Francisco Pizarro, in Peru in 1531 (García 2003). In consequence, these communities were much more vulnerable when the Spanish arrived.

Those are just some examples of the diseases that were present in America in colonial times. It would be possible to also name measles, typhus, and yellow fever, among others. As said above, these diseases were introduced by external agents to communities with a lack of immunity to such pathogens and in consequence were defenseless. The conquest of the continent and its peoples could be explained to some extent by the contribution of non-human agents as a silent army that besides the imposition of new socioeconomic order results in the breakdown of the indigenous structures and the fall of the main pre-Hispanic cities.


Cordero del Campillo, M. (2001). Crónicas de Indias. Junta de Castilla y León, Consejería de Educación y Cultura.

Crosby, A. W. (1976). Virgin soil epidemics as a factor in the aboriginal depopulation in America. The William and Mary Quarterly: A Magazine of Early American History, 289-299.

De Las Casas, B. (1877). Historia de las Indias (Vol. 1). Imprenta y litografia de I. Paz. García Cáceres, U. (2003). La implantación de la viruela en los Andes, la historia de un holocausto. Revista Peruana de Medicina Experimental y Salud Pública, 20(1), 41-50.

Koch, A., Brierley, C., Maslin, M. M., & Lewis, S. L. (2019). Earth system impacts of the European arrival and Great Dying in the Americas after 1492. Quaternary Science Reviews, 207, 13-36.

McCaa, R. (1995). Spanish and Nahuatl Views on smallpox and demographic catastrophe in Mexico. The Journal of interdisciplinary history, 25(3), 397-431. McNeill, W. H., & McNeill, W. (1998). Plagues and peoples. Anchor.