Clinical Manifestations
Symptoms of shigellosis include abdominal pain, tenesmus?, watery diarrhea, and/or dysentery (multiple scanty, bloody, mucoid stools). Other signs may include abdominal tenderness, fever, vomiting, dehydration, and convulsions.
Structure, Classification, and Antigenic Types
Shigellae are Gram-negative, nonmotile, facultatively anaerobic, non-spore-forming rods. How could Shigella are differentiated from the closely related Escherichia coli ????
on the basis of pathogenicity?, physiology? (failure to ferment lactose or decarboxylate lysine) and serology?.
The genus is divided into four serogroups with multiple serotypes: A (S dysenteriae, 12 serotypes); B (S flexneri, 6 serotypes); C (S boydii, 18 serotypes); and D (S sonnei, 1 serotype).
Pathogenesis
Infection is initiated by ingestion of shigellae (usually via fecal-oral contamination). An early symptom, diarrhea (possibly elicited by enterotoxins and/or cytotoxin), may occur as the organisms pass through the small intestine. The hallmarks of shigellosis are bacterial invasion of the colonic epithelium and inflammatory colitis?. These are interdependent processes amplified by local release of cytokines and by the infiltration of inflammatory elements?. Colitis in the rectosigmoid mucosa?, with concomitant malabsorption?, results in the characteristic sign of bacillary dysentery: scanty,. unformed stools tinged with blood and mucus?.
Host Defenses
Inflammation, copious mucus secretion, and regeneration of the damaged colonic epithelium limit the spread of colitis and promote spontaneous recovery?. Serotype-specific immunity is induced by a primary infection, suggesting a protective role of antibody recognizing the lipopolysaccharide (LPS) somatic antigen. Other Shigella antigens include enterotoxins, cytotoxin, and plasmid-encoded proteins that induce bacterial invasion of the epithelium. The protective role of immune responses against these antigens is unclear.Copyright © 1996
The University of Texas Medical Branch at Galveston