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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 infection, however, since an infected person can become reinfected by the same species of Shigella.

Once the bacterium has gained entrance through the mouth it travels to the lower intestine (colon) where it penetrates the mucosa (lining) of the intestine. In severe cases the entire colon may be involved, but usually only the lower half of the colon is involved. The incubation period is one to four days, that is the time from infection until symptoms appear.

Symptoms may be sudden and severe in children. They experience abdominal pain or distension, fever, loss of appetite, nausea, vomiting, and diarrhea. Blood and pus will appear in the stool, and the child may pass 20 or more bowel movements a day. Left untreated, he will become dehydrated from loss of water and will lose weight rapidly. Death can occur within 12 days of infection. If treated or if the infection is weathered, the symptoms will disappear within approximately two weeks.

Adults experience a less severe course of disease. They will initially feel a griping pain in the abdomen, develop diarrhea, though without any blood in the stool at first. Blood and pus will appear soon, however, as episodes of diarrhea recur with increasing frequency. Dysentery usually ends in the adult within four to eight days in mild cases and up to six weeks in severe infections.

Shigella dysenteriae brings about a particularly virulent infection that can be fatal within 12-24 hours. The patient has little or no diarrhea, but experiences delirium, convulsions, and lapses into a coma. Fortunately infection with this species is uncommon.

Treatment of the patient with dysentery usually is by fluid therapy to replace the liquid and electrolytes lost in sweating and diarrhea. Antibiotics may be used, but some Shigella species have developed resistance to them, so they may be relatively ineffective. Fluid therapy should be tendered with great care because patients often are very thirsty and will overindulge in fluids if given access to them. A hot water bottle may help to relieve abdominal cramps.

Some individuals can harbor the bacterium without having symptoms. Like those who are convalescent from the disease, the carriers without symptoms can spread the disease. This may occur by someone with improperly washed hands preparing food, which becomes infected with the organism.

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Science EncyclopediaScience & Philosophy: Direct Variation to DysplasiaDysentery - Shigellosis, Amebic Dysentery