Diagnosis, Clincial Manifestations, and Pathology

Diagnosis is by clinical signs, cultivation of Shi­gella or other bacteria from tissue swabs and feces, and serologic tests to determine species and strains. Differential diagnosis must exclude other agents of dysentery, including other bacteria, viruses, and amebas.

Bacteria invade the mucosa of the large intestine, where they cause mucus secretion, edema, and, usu­ally, superficial ulceration and bleeding. The watery diarrhea is probably caused by a toxin that increases the secretions of the cells of the intestinal wall.

The incubation period is from 1 to 4 days. Onset is sudden in children, with fever, drowsiness or irrita­bility, anorexia, nausea, abdominal pain, tenesmus, and diarrhea. Blood, pus, and mucus appear in the diarrheal stools within 3 days. Increasingly frequent watery stools cause dehydration, and death can oc­cur as early as 12 days. If the patient survives, recovery usually begins after about 2 weeks. In adults, there is usually no fever, and the disease generally resolves itself after 1 to 6 weeks. Symp­toms in both children and adults may vary from simple, transient diarrhea to acute dysentery and death.

It is not always possible to differentiate amebic and bacillary dysentery on clinical grounds, but shigellosis generally has a more sudden onset and more acute course, is more likely to occur in explo­sive epidemics, and is not a chronic disease. Tenes­mus is a much more common symptom in shigellosis, and the stools are generally less abundant and con­tain more bright red blood than in typical cases of amebic dysentery.