ERADICATION OF DISEASE

A communicable disease is considered to be eradicated when all transmission has ceased and the causal agent has been exterminated. This may have happened naturally with some epidemic diseases that flourished in the past, such as the sweating disease epidemics that occurred in medieval Europe. Smallpox eradication was accomplished by 1980 through a carefully planned campaign conducted by the World Health Organization.

Eradication relies on a combination of surveillance and control—surveillance to identify the focal point of the infection, and control measures to treat active cases and remove the risk of transmission. Control measures will vary according to the causal agent and its mode of transmission. With smallpox, the effective strategy was containment—every diagnosed case of smallpox was isolated and all known contacts of every case received the smallpox vaccine. This created a situation in which the virus was not able to migrate to a susceptible host, and since the smallpox virus lives only in humans, all natural transmission was blocked. The disease was eliminated from one region after another, and eventually eradicated worldwide—one of the greatest triumphs ever for preventive medicine.

In countries and regions where vaccination against measles and poliomyelitis are virtually universal, national or regional eradication of these diseases is feasible; this is described as elimination, rather than eradication, because the possibility always exists for reintroduction of the causal agent from parts of the world where the disease still occurs.

John M. Last

(see also: Disease Prevention; Immunizations; Measles; Poliomyelitis; Smallpox )