Smallpox

Epidemic smallpox was one of the deadliest scourges ever to afflict humankind. It killed ancient Egyptian Pharoahs, villagers in teeming Asian villages, aristocrats in Paris and St. Petersburgh, and children in colonial New England. It contributed substantially to the collapse of the Aztec empire in Mexico, where it was introduced by the Spanish conquistadors. It was an ever-present threat, always lurking, occasionally breaking out in large epidemics. Smallpox occurred in two forms, variola major and variola minor. Variola major was the fulminant, often epidemic, variety, with a mortality rate of 40 percent or more and severe complications among survivors. Variola minor was more mild, with a mortality rate of less than 5 percent.

About 1,000 years ago, Chinese physicians discovered that susceptible persons inoculated with secretions from a smallpox scab generally had only a mild attack, and thereafter were immune. This procedure, called variolation, reached Constantinople about 1700, and was reported in a letter by Lady Mary Wortley Montagu, wife of the British plenipotentiary, to a friend in England in 1717. In 1798, Edward Jenner, a Gloucestershire doctor, vaccinated a boy with secretions from a cowpox blister, and soon reported successful vaccination of over twenty others. This was the prelude to the twentieth-century eradication of smallpox in a worldwide vaccination campaign coordinated by the World Health Organization. The last naturally occurring case was a girl in Somalia in 1977 (two further laboratory cases occurred in England in 1978).

Smallpox was an acute illness with high fever, a widespread skin rash with blebs and blisters, generalized prostration, collapse, and, commonly, death. Survivors often carried disfiguring scars for the rest of their lives, and were usually blind if lesions affected their eyes. The cause was a brickshaped virus in the orthopox virus family. Humans were its only natural host. The virus survives now only in tissue cultures in two or three high-security microbiology research institutes. Total eradication was made possible by unique epidemiological features—i.e., there is no nonhuman host and vaccination was rapidly efficacious, so those who had been exposed to a case were protected from infection if they were immediately vaccinated. This was the basis for the containment strategy that was ultimately the key to global eradication.

Smallpox has been identified as a potential biological weapon. It would wreak havoc in an unvaccinated population, and it would be difficult for a vulnerable nation to mount an effective vaccination campaign in time to prevent national devastation. However, attackers who used smallpox as a weapon would have to ensure that they were all vaccinated, and it would be difficult to conceal a vaccination program against smallpox from the world.

JOHN M. LAST

(SEE ALSO: Communicable Disease Control; Epidemics; Immunizations; Jenner, Edward; Montagu, Lady Mary Wortley)