HIST103: World History (1600–Present)

The Spread of Disease from the Old World to the New

The list of infectious diseases that spread from the Old World to the New is long; the major killers include smallpox, measles, whooping cough, chicken pox, bubonic plague, typhus, and malaria. Because native popula­tions had no previous contact with Old World diseases, they were immunologically defenseless.

Dobyns writes that "before the invasion of peoples of the New World by pathogens that evolved among inhabitants of the Old World, Native Americans lived in a relatively disease-free environment. . .. Before Europeans initiated the Columbian Exchange of germs and viruses, the peoples of the Americas suffered no smallpox, no measles, no chickenpox, no influenza, no typhus, no typhoid or parathyroid fever, no diphtheria, no cholera, no bubonic plague, no scarlet fever, no whooping cough, and no malaria".

Although we may never know the exact magnitudes of the depopulation, it is estimated that upwards of 80-95 percent of the Native American population was decimated within the first 100-150 years following 1492. Within 50 years following contact with Columbus and his crew, the native Taino population of the island of Hispaniola, which had an estimated population between 60,000 and 8 million, was virtually extinct. Central Mexico’s population fell from just under 15 million in 1519 to approximately 1.5 million a century later. Historian and demographer Nobel David Cook estimates that, in the end, the regions least affected lost 80 percent of their populations; those most affected lost their full populations; and a typical society lost 90 percent of its population.

The uncertainty surrounding the exact magnitude of the depopulation of the Americas arises because we don’t know the extent to which disease may have depopulated the regions beyond the initial point of contact before literate European observers made physical contact with these populations. If disease traveled faster than the explorers, it would have killed a significant portion of native populations before direct contact, causing first-hand accounts of initial population sizes to be biased downward.

The result is that 1491 population estimates for the Americas have varied wildly, from a lower-bound estimate of approximately 8 million to an upper-bound estimate of over 110 million people. Surprisingly, despite decades of research, the range of the estimates has not narrowed, and no clear consensus has emerged about whether the true figure lies closer to the high or low end of the range. For examples of the opposing views, see Henige and Mann.

Syphilis: A New World Disease?

There are very few examples of disease being spread from the New World to the Old. The most notable exception, and by far the most controversial, is venereal syphilis. Biologist Irwin Sherman lists venereal syphilis as one of the twelve diseases that changed the world. This may seem surprising, given that, today, venereal syphilis is a nonfatal disease that is effectively treated with penicillin. However, this was not always the case.

Early on, in the late 15th and early 16th centuries, the disease was frequently fatal, and its symptoms were much more severe. They included genital ulcers, rashes, large tumors, severe pain, dementia, and eventual death. Over time, as the disease evolved, its symptoms changed, becoming more benign and less fatal. By the 17th century, syphilis had developed into the disease that we know today.

Two theories of the origins of venereal syphilis exist. The first, referred to as the "Columbian hypothesis," asserts that the disease-causing agent Treponema pallidum originated in the New World and was spread in 1493 by Christopher Columbus and his crew, who acquired it from the natives of Hispaniola through sexual contact. Upon return to Spain, some of these men joined the military campaign of Charles VIII of France and laid siege to Naples in 1495. 

Encamped soldiers exposed the local populations of prostitutes, which amplified disease transmission. Infected and disbanded mercenaries then spread the disease throughout Europe when they returned home. Within five years of its arrival, the disease was epidemic in Europe. Syphilis reached Hungary and Russia by 1497; Africa, the Middle East, and India by 1498; China by 1505; Australia by 1515; and Japan by 1569.

The second theory, the "pre-Columbian hypothesis," asserts that the disease had always existed in the Old World, and the fact that there were no accounts of the disease prior to the 1490s is because, prior to this time, it had not been differentiated from other diseases with similar symptoms. Proponents of the pre-Columbian hypothesis cite pre-Exchange accounts of disease symptoms similar to venereal syphilis, as well as skeletal remains with scars that are similar to scars left by syphilis. The debates over the true origins of venereal syphilis have been a direct consequence of the difficulty in distinguishing venereal syphilis from other diseases that had similar symptoms and left similar bone scars.

Recent findings from phylogenetics (the evolutionary study of the genetic relat­edness of different populations of organisms) have added valuable evidence to the mystery of the origins of venereal syphilis. The evidence supports the Columbian hypothesis that venereal syphilis is, in fact, a New World disease. A recent study by Harper et al. found that the bacterium causing venereal syphilis arose relatively recently in humans and is most closely related to a variation of the tropical disease yaws found in a remote region of Guyana, South America. This relationship is most consistent with venereal syphilis or some early ancestor originating in the New World. After decades of debate, this powerful study showed that venereal syphilis was indeed a New World disease.