Definition of Smallpox

Smallpox: Also known as variola, a highly contagious and frequently fatal viral disease characterized by a biphasic fever and a distinctive skin rash that left pock marks in its wake. Because of its high case-fatality rates and transmissibility, smallpox now represents a serious bioterrorist threat. The disease is caused by the variola virus. The incubation period is about 12 days (range: 7 to 17 days) following exposure. Initial symptoms include high fever, fatigue, and head and back aches. A characteristic rash, most prominent on the face, arms, and legs, follows in 2-3 days. The rash starts with flat red lesions that evolve at the same rate. Lesions become pus-filled and begin to crust early in the second week. Scabs develop and then separate and fall off after about 3-4 weeks.

The majority of patients with smallpox recover, but death occurs in up to 30% of cases. Smallpox is spread from one person to another by infected saliva droplets that expose a susceptible person having face-to-face contact with the ill person. Persons with smallpox are most infectious during the first week of illness, because that is when the largest amount of virus is present in saliva. However, some risk of transmission lasts until all scabs have fallen off. Smallpox was so named because the pocks were small and the disease was seen as less than the "great pox" (syphilis). Smallpox is also known as variola.

The English physician Edward Jenner (1749-1823) exploited the fact that cowpox created immunity to smallpox to create a vaccine for smallpox. Jenner took coxpox from a milkmaid who had contracted it from an infected cow and innoculated an 8-year-old boy with the cowpox and then exposed him to smallpox -- an experiment questionable on ethical grounds. Aside from Jenner, other participants in this historic experiment were Sarah Nelmes (the milkmaid), James Phipps (the young boy), and Blossom (the cow).

In America the first physician to promote the use of Jenner's vaccine was Benjamin Waterhouse (1754-1846), professor of the theory and practice of physic at Harvard Medical School. Waterhouse inoculated his son and the rest of his household in 1800 to prove the value of the vaccine. (Experimenting on near and dear ones is frowned upon today).

Smallpox is one of the success stories of medicine. Thanks to vaccination, smallpox was eradicated from the globe in 1977.