The early history of European and African settlement in the Western Hemisphere provides a depressingly long list of epidemics and pandemics. Many of these occurred on a large geographical scale, sparked by the contact of Native American communities with immigrant men and women who carried deadly pathogens to which the carriers themselves were immune or highly resistant. In turn, these intruders were susceptible to Native American diseases, one example of which may have been syphilis. It seems that some infected Spanish explorers contracted that sexually transmitted disease (STD) and spread it after their return to Europe. For their part, Native Americans died by the thousands of imported Old World diseases such as measles, mumps, smallpox, typhus, and influenza. This biological interaction is sometimes referred to as part of the “Columbian Exchange,” taking its name from the Italian explorer Christopher Columbus.
Although early immigrants from Europe and Africa tended to share resistance to a wide range of pathogens, later generations, long removed from their homelands and isolated fromcertain diseases in the New World, tended to lose their natural defenses to the OldWorld diseases. When new immigrants arrived from the Old World, even from the same cities and regions as the ancestors of secondor third-generation colonists or slaves, their reinfusion of disease-causing pathogens could and often did trigger outbreaks—even epidemics— among the settled immigrants populations. Perhaps ironically, however, this was least likely to occur in large cities such as New York, Boston, and Philadelphia, in which steady streams of new immigrants kept levels of exposure and resistance relatively high among the urban populations.
Some imported diseases, such as mosquitoborne malaria and yellow fever, were initially and inadvertently inserted into humid coastal environments in the NewWorld that were well suited to the insects by Spanish slavers and their human cargoes. While the African immigrant populations were generally resistant to the potentially deadly diseases, both Native Americans and Europeans proved to be highly susceptible. The insects became carriers when they sucked the blood of human carriers. In regions where human carriers diminished in number, as along the northern Atlantic coastline (thanks in part to the practice of quarantine), the incidence of the disease dropped off. Fresh arrivals of African or Caribbean slaves along the southern U.S. coasts, however, helped maintain high incidence levels. Even beforeWalter Reed and other researchers untangled the true nature of yellow fever during the early twentieth century, Americans sought strict limitations on immigrants and even trade from Cuba and other island sources of the disease whose carriers set off recurrent outbreaks.