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Book Antiqua:

1 Shigella Dr.Gogoi;University of Fiji


2 Shigella Belong to Enterobacteriaceae Non motile , non capsulated NLF on MAC Deoxycholate citrate agar (DCA) selective media (pale color colonies) Gram negative bacilli

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3 Shigella species Mannitol Non Fermentation Fermentation S dysentriae -12 S flexneri- 6 S boydii - 18 S sonnei (Late lactose fermenter)

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4 Epidemiology and Clinical Syndromes Major cause of bacillary dysentery Outbreaks in daycare centers, nurseries, institutions Estimated 15% of pediatric diarrhea in U.S. Leading cause of infant diarrhea & mortality in developing countries Epidemics of S. dysenteriae type 1 have occurred in Africa and Central America with case fatality rates of 5-15%. Common in P ediatric age group (1-10 yrs) Developed world – S sonnei , developing world – S flexneri


5 Epidemiology and Clinical Syndromes Shigellosis = Generic term for disease Low infectious dose (10 2 -10 4 CFU) Humans are only reservoir Transmission by fecal-oral route Incubation period = 1-3 days Watery diarrhea with fever; changing to dysentery Bacillary Dysentry Passing blood & mucus in the stool

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6 Infection cycle of Shigella Shiga toxin exacerbate inflammation by causing ishchemia & hemorrhage Ulcers Rarely lead to bacteremia Organisms adhere to colonic lymphoid follicles Undergo parasite directed phagocytosis Resist intracelluar killing Move directly from cell to cell SMALL GUT LARGE GUT STOMACH


7 Pathogenesis Two-stage disease Early stage Second stage Fever attributed to neurotoxic activity of toxin D ysentery due to a dherence and tissue invasion of large intestine ( c ytotoxic activity of Shiga toxin ) Watery diarrhea attributed to the enterotoxi n activity of Shiga toxin in the small intestine Enterotoxic , neurotoxic and cytotoxic Shiga toxin Similar to Shiga-like toxin of E nterohemorrhagic E. coli (EHEC)


8 Virulence factors Invasiveness Attachment (adherence) and internalization with complex genetic control Large multi-gene virulence plasmid regulated by multiple chromosomal genes Intracellular survival & multiplication Exotoxin (Shiga toxin) Complications : Hemolytic uremic syndrome and reiters syndrome

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9 Clinical manifestation Fever Abdominal cramping & tenderness Diarrhea / Dysentry Tenesmus (straining at stools Sigmoidoscopy: ulceration

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8/11/2013 10 Lab Diagnosis of Dysentry Specimens Stool, rectal swab from an ulcer ( buffered glycerol saline - transport medium) Culture MAC NLF colonies AST Report & Interpretations TSI agar K - / A - DCA NLF

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11 Shigella Dysentry- Differentiated from Dysentry like diseases Entero invasive E coli Campylobacter jejuni Entamoeba histolytica Balantidium coli

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12 Treatment For adults No vaccines Rehydration if necessary For children Co-trimoxazole or ampicillin + rehydration Norfloxacin or ciprofloxacin Water supply Sewage maintenance Human carriers identified & treated Breast feeding than formulas Prevention

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13 Summary Bacillary Dysentry Clinical manifestation Species of Shigella Pathogenesis Virulence factors Source and spread Laboratory diagnosis Antibiotics used Preventive measures

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