SHIGELLA Bacillary dysentry

ETIOLOGY Shigella dysenteriae Shigella dysenteriae Shigella flexneri Shigella flexneri Shigella boydii Shigella boydii Shigella sonnei Shigella sonnei Natural habitat-intestinal tract Natural habitat-intestinal tract

Morphology & identification Gram negative non motile bacilli Gram negative non motile bacilli Facultative anaerobes Facultative anaerobes Grow on ordinary culture media Grow on ordinary culture media Enrichment media - Selenite F broth Enrichment media - Selenite F broth - Tetrathionate broth - Tetrathionate broth Selective media - Salmonella shigella agar Selective media - Salmonella shigella agar - Deoxycholate citrate agar - Deoxycholate citrate agar

Antigenic structure - somatic O antigen - More than 40 serotypes - More than 40 serotypesPATHOGENESIS Infections-limited to gastrointestinal tract Infections-limited to gastrointestinal tract Blood stream invasion is rare Blood stream invasion is rare Infective dose 10 3 organisms Infective dose 10 3 organisms Essential pathologic process Essential pathologic process - lnvasion of mucosal epithelial cells,escape from phagocytic vacuoles - lnvasion of mucosal epithelial cells,escape from phagocytic vacuoles

Multiplication spread within cytoplasm Multiplication spread within cytoplasm passage to adjacent cells passage to adjacent cells Microabscess --necrosis of mucous membrane, Microabscess --necrosis of mucous membrane, superficial ulceration,bleeding, superficial ulceration,bleeding, Pseudomembrane formation Pseudomembrane formation TOXINS TOXINS A. Endotoxin A. Endotoxin Lipopolysaccharides --- irritation of bowel wall Lipopolysaccharides --- irritation of bowel wall

B. Shigella dysenteriae exotoxin B. Shigella dysenteriae exotoxin Heatlabile Heatlabile Affect the gut and CNS Affect the gut and CNS Enterotoxin - produce diarrhoea Enterotoxin - produce diarrhoea Neurotoxin - meningismus and coma Neurotoxin - meningismus and coma Two act in sequence, toxin producing an early Two act in sequence, toxin producing an early voluminous diarrhoea and invasion of large voluminous diarrhoea and invasion of large intestine resulting in later dysentery intestine resulting in later dysentery

Clinical findings I ncubation period - 1 to 2 days I ncubation period - 1 to 2 days Abdominal pain, fever, diarrhoea, later number of stool increase which contain mucous and blood Abdominal pain, fever, diarrhoea, later number of stool increase which contain mucous and blood Straining, tenesmus Straining, tenesmus Subside spontaneously in days Subside spontaneously in days In children and elderly - dehydration, acidosis, death In children and elderly - dehydration, acidosis, death Shigella dysenteriae type 1 Shigella dysenteriae type 1 -Haemolytic uraemic syndrome -Haemolytic uraemic syndrome Carrier - recurrent bout of disease Carrier - recurrent bout of disease

Laboratory diagnosis Specimen Fresh stool, mucous flecks, rectal swab for culture Fresh stool, mucous flecks, rectal swab for culture Serum for serology Serum for serologyCulture MacConkey’s agar, Salmonella Shigella agar, MacConkey’s agar, Salmonella Shigella agar, Hektoen enteric agar Hektoen enteric agar Biochemical test - non lactose fermenter. - non lactose fermenter. - ferment other carbohydrates – acid production - ferment other carbohydrates – acid production

Serology Serology - Slide agglutination test - Slide agglutination test using - species specific sera using - species specific sera - type specific sera - type specific sera Antibiotic sensitivity test Antibiotic sensitivity test

Immunity Type specific antibody response Type specific antibody response - Fail to protect against infection - Fail to protect against infection Ig A - limits reinfection Ig A - limits reinfectionTreatment - Ciprofloxin, ampicillin, tetracycline, chloramphenicol - Ciprofloxin, ampicillin, tetracycline, chloramphenicol - Multi-drug resistance – transmitted by plasmids - Multi-drug resistance – transmitted by plasmids

Epidemiology, Prevention & Control Transmission - food, fingers, faeces & flies Transmission - food, fingers, faeces & flies Mostly - children under 10 years of age Mostly - children under 10 years of age Control efforts Control efforts - sanitary control of water,food and milk; - sanitary control of water,food and milk; - proper sewage disposal and fly control - proper sewage disposal and fly control - isolation of patients, disinfection of excreta - isolation of patients, disinfection of excreta - detection of subclinical cases and carriers, - detection of subclinical cases and carriers, (food handlers) (food handlers)

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