Rarely Does Carriage of the Bacilli Persist as Long as Three Months
Rarely does carriage of the bacilli persist as long as three months. Although Shigella infection is largely confined .to human beings, primates have been shown occasionally to be a source of infection in man. Shigella survive in eggs, oysters, clams, and shrimp for many days, but these serve as sources of infection only when contaminated by infected persons and their excreta. Pathogenesis and Pathology. Shigella dysenteriae • (Shiga) produces an exotoxin that can exert a deleterious effect upon the nervous system. The occurrence of paralytic manifestations in dysentery produced by this species may be attributable to the exotoxin.
Morphologic lesions are most frequently observed in the colon, occasionally involving the terminal ileum. Ulceration of the mucosa develops, with intervening inflamed membrane but no undermining of the ulcer edges as in amebic dysentery. The bowel wall is infiltrated with granulocytes, there is edema of the submucosa, and occasionally the involvement may extend to the serosa.
If ulceration is not ex-tensive, healing occurs without scarring, but when it is severe, fibrosis and even stenosis of the bowel may develop. Clinical Manifestations. It has been proposed that bacillary dysentery may occasionally be responsible for chronic colitis, but it has been difficult to establish this relationship with certainty. The incubation period of dysentery is usually about 48 hours, but it may be shorter. occasionally containing blood. Abdominal tenderness, most pronounced in the lower quadrants, is found, and .the bowel is hyperactive on auscultation. or more.
Acute gastroenteritis, associated with nausea, some vomiting, and diarrhea, is seen particularly in outbreaks of infection by Shigella sonnei. The fever may be higher, hypotension develops more frequently, and the intestinal symptoms are more intense. Recovery may be delayed, and debility may persist for several weeks. At times, bacillary dysentery seems to have been precipitated by the onset of measles, and almost half the cases may be accompanied by infection with enteropathic viruses including adenovirus, echovirus, poliovirus, and Coxsackie virus. but it is not ordinarily useful for diagnostic purposes. Shigella survive in feces for only a short while.
Therefore, feces should be promptly cultured, or the specimen should be collected in a 30 percent glycerol-saline solution for preservation. Examination of the feces microscopically in bacillary dysentery will usually reveal a large number of granulocytes, comprising about 90 percent of all cells, apart from erythro-cytes. This test agrees with cultural results in over 90 percent of instances. Viral enteritis caused by echovirus, Coxsackie, and poliomyelitis viruses may be epidemic and maybe confused_ with shigellosis.