Encyclopedia of the Incas

one that changed traditional ways of doing things in profound ways. The
exchange was two sided, as Old and New Worlds collided, shook, and ultimately
transformed the globe. The exchange involved the movement across the Atlantic
and Pacific Oceans of long-separated peoples, taking with them their plants and
animals, and their pathogens.
Of the three principal elements of the Columbian Exchange, disease caused by
pathogens, resulting in sickness and untimely death, had the greatest and most
immediate impact on the peoples of the Americas. Pathogens are any foreign
agents entering the body that can cause disease. Broadly the pathogens are
viruses, bacteria, parasites, protozoa, and fungi. Just to list their names would
consume several pages. With the coming of the agricultural revolution and rising
populations, the peoples of linked Eurasia and Africa experienced the heavy
impact of pathogens. It appears there was a greater diversity of pathogens in the
Old World than in the Americas, and there was substantial regional specificity.
The New World was not a disease-free environment. It too went through the
agricultural revolution and the rise of cities, and faced the impact of pathogens.
A large number of autochthonous Andean diseases also debilitated or killed
victims outright (see Health and Illness). Syphilis, tuberculosis, and
leishmaniasis were endemic, and there were various hemorrhagic fevers.
Parasites were ubiquitous. But the introduction of Old World disease as part of
the Columbian Exchange caused exceptional mortality.
The principal early culprits were smallpox and measles—acute, easily
communicable viruses that could spread rapidly, especially in areas of high
population density. Both require a chain of infection, otherwise an epidemic will
burn itself out. In densely populated areas of the Old World both diseases tended
to be endemic, affecting mostly children. Measles, especially complications
resulting from it, took 10–15 percent of victims, whereas smallpox wiped out 25
percent or more with each flare-up. Smallpox and measles survivors developed
lifelong immunity. Some experienced subclinical infections (mild cases with no
visible symptoms) that provided some immunity in future outbreaks, too.
Infected individuals can carry the virus several days before the onslaught of
sickness, therefore the infection can be carried in advance of any knowledge of
it.
Smallpox and measles were relatively easy for Spanish physicians of the
period to identify by their symptoms, and the differences were known and
described as early as the tenth century in a medical text by the Persian physician
Rhazes. The arrival of the vectored diseases, such as typhus, plague, malaria,