Epidemic diseases, introduced from both tropical Africa and Western Europe were frequent visitors to the British North American colonies during the late colonial period and to the United States during the early years of the new nation. The two major epidemic diseases that broke out in the period from 1754 to 1829 were smallpox from the British Isles and yellow fever from West Africa via the West Indies. A number of other diseases, including diphtheria, scarlet fever, measles, whooping cough, and mumps also appeared in epidemic form and swept parts of eastern North America. This vulnerability to exotic disease continued through the nineteenth century. Cholera, spreading from an initial outbreak in South Asia, struck the United States of America for the first time in 1831 and 1832.
Epidemics typically broke out among urban populations that had little or no immunological experience with the pathogen. The outbreaks could be spectacularly frightful and impress themselves into cultural memory. Yellow fever and smallpox wreaked concentrated havoc in cities and spread terror and sickening fear both within and outside the immediate zones of infection.
Epidemics of yellow fever, a mosquito-borne viral disease, were spread by the arrival in port cities of ships from the West Indies, where the disease was endemic. The transmission of yellow fever depended upon an infected individual being bit by an Aedes aegypti mosquito that would in turn bite an uninfected individual. The first epidemics in the British North American colonies took place in the late seventeenth century. A succession of epidemics occurred in the mid-eighteenth century. Philadelphia was struck twice in the 1740s, once in 1762, and then three times in the 1790s. The most famous of these was the 1793 epidemic that killed nearly four thousand, sweeping away to death 10 percent of the urban population. In the early nineteenth century, yellow fever epidemics began to strike the southern ports of New Orleans, Mobile, Charleston, and Savannah. The only effective public health policy was the imposition of quarantine upon ships that were known or suspected to carry the disease.
The yellow fever outbreaks rent the fabric of family and community life. The means of transmission was unknown, and the disease was feared to be contagious. As ever, desperate circumstances brought out the worst and the best. Some families abandoned their sick. Others stayed to nurse their loved ones through the moment of death. The wealthy took flight from the cities; the poor were left to the ravages of the disease. The high fevers and characteristic black vomit that signaled the approach of death inspired particular horror and unleashed racial fears and prejudices. In Philadelphia, African Americans volunteered to care for the sick and did so valiantly; after the epidemic had receded, fearful whites blamed them for the outbreak.
Smallpox was also a deadly viral disease, but unlike yellow fever, it was highly contagious and spread directly from human to human. Immigrants from the British Isles, where smallpox infection was endemic and the principal victims were children, introduced it into the British North American colonies. There, the disfiguring pox destroyed both old and young; survivors of smallpox carried their immunities into adulthood, but the disease never became fully endemic and thus new generations reached adulthood without immunity. In the colonies, smallpox leapt beyond the communities of whites and their slaves into the worlds of the Native Americans, where it wreaked disaster. The death rates among Native Americans are thought to have ranged from 25 to 50 percent. During the epidemic of 1775-1782, smallpox ravaged most of the North American continent, killing more than one hundred thousand and disfiguring many more.
Until the late eighteenth century, the only recourse against smallpox infection was a form of inoculation known as variolation that had been in occasional use since the 1720s. Variolation was dangerous; it involved the intentional subcutaneous introduction of smallpox pus and produced immunity in the 95 percent of the initiates who survived the procedure. The first enforced use of this technique took place during the American Revolution, when General George Washington made the decision to inoculate by variolation all of the troops of the Continental Army. At the end of the eighteenth century, a new type of inoculation, known as vaccination, used what is thought to have been either a cowpox or horsepox virus that proved safe and effective. The broad acceptance of vaccination in the United States reduced greatly the threat of smallpox and constituted a major advance in the efficacy of public health interventions.