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326Mdiar - Diarrhea and its etiology Diarrhea 1...

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Diarrhea and its etiology Diarrhea- 1. secretory (non-invasive loss of fluids and electrolytes) caused by enterotoxins and 2. invasive (tissue damaging); transmission by the 7 F's: feces, food, flies, fluids, fingers, fomites, fornication; world has a fecal "veneer" ! In addition to diarrhea, can cause systemic diseases like typhoid ( Salmonella typhi ) and plague ( Yersinia pestis ) Food borne disease is one of the most under reported, but in most cases can be entirely prevented!!!! Shigella Shigella : four groups- each a separate species- infect only humans and higher primates (apes); very small inoculum: 10- 1000 organisms! Shigella dysenteriae (GpA) type 1 causes most severe disease-only Shigella to make shiga toxin; epidemic of fatal dysentery in early 20th century, disappeared after WW I; reemerged in Guatemala in 1969 (↑ mortality); also now seen in Africa and Asia Shigella sonnei (GpD)- emerged after WW II; is predominant group in USA; causes "mildest" illness; becoming very drug resistant! Entry, multiplication, spread: resist stomach acidity- special proteins expressed under adverse conditions; enter intestine- invade colonic epithelial cells- plasmid encoded outer membrane proteins (invasion plasmid Ags, IPAs) direct parasite mediated endocytosis; multiply and spread from cell to cell; results in shallow mucosal ulcers thru which RBC and WBC exude to produce the dysenteric
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stool; also inflammatory response in lamina propria (connective tissue coat just below intestinal epithelium and basement membrane Damage- endocytosis results in mucosal epithelial damage; cytotoxin further damages the epithelia; shiga toxin (ST) inactivates 60s ribosomal subunit- cessation of protein synthesis Diagnosis and treatment- isolate the organism from stool quickly; use transport medium; perform serogrouping and biochemical tests; oral rehydration therapy (ORT); antimicrobial agents to reduce the infectious period (nalidixic acid and other quinolones); do not stop gut motility !!! no vaccine yet, but a living attenuated one-in development Salmonella Salmonella - taxonomy is in dispute; has many serotypes (serovars); serotypes are distinguished by somatic (O) LPS Ag; and flagellar (H) Ag; many of the serotypes are “nonhost” adapted strains- affect many species of animals
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Encounter and entry- large inoculum (10 7
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