Dysentery is an infectious disease that has ravaged armies, refugee camps, and prisoner-of-war camps throughout history. The disease still is a major problem in developing countries with primitive sanitary facilities.

The acute form of dysentery, called shigellosis or bacillary dysentery, is caused by the bacillus (bacterium) of the genus Shigella, which is divided into four subgroups and distributed worldwide. Type A, Shigella dysenteriae, is a particularly virulent species. Infection begins from the solid waste from someone infected with the bacterium. Contaminated soil or water that gets on the hands of an individual often is conveyed to the mouth, where the person contracts the infection. Flies help to spread the bacillus.

Young children living in primitive conditions of overcrowded populations are especially vulnerable to the disease. Adults, though susceptible, usually will have less severe disease because they have gained a limited resistance. Immunity as such is not gained by...