Chapter 33, Ep 4 of 5: Parasitic and Viral Diarrheas

The parasitic diarrheas sort by exposure history, so the workup follows the suspected pathogen rather than a generic ova-and-parasite exam. Giardia comes from untreated water with a single-dose tinidazole answer, Entamoeba histolytica from endemic travel with two-stage tissue-then-luminal therapy, and Strongyloides is the pre-steroid serology question that prevents seventy-percent-mortality hyperinfection. Anisakis is the raw-fish larva cured by endoscopic removal. On the viral side, norovirus dominates on infectious dose and environmental persistence, which is why soap-and-water and bleach are the outbreak answers, while rotavirus fades under vaccination.   Topics covered Suspecting parasites by exposure history Giardia and single-dose tinidazole Cryptosporidium and immune status Entamoeba histolytica two-stage therapy Strongyloides pre-steroid screening and hyperinfection Anisakis and endoscopic removal Norovirus and the outbreak pattern Rotavirus and the viral differential   Key decisions Diagnose Giardia by stool antigen EIA or PCR over insensitive microscopy, and treat with single-dose tinidazole two grams, choosing paromomycin in pregnancy because it is poorly absorbed. Treat Entamoeba histolytica sequentially: metronidazole or tinidazole for tissue-invasive trophozoites, followed by a luminal agent like paromomycin to kill the cysts that would otherwise relapse. Manage most amebic liver abscesses with metronidazole alone, reserving drainage for large or peripheral abscesses at risk of rupture or for treatment failure. Screen with Strongyloides serology before any glucocorticoid, anti-TNF agent, transplant immunosuppression, or chemotherapy in patients with prior endemic exposure, since stool studies are insensitive. Treat Strongyloides with ivermectin over albendazole because ivermectin targets the autoinfective filariform larvae, and give empiric ivermectin when immunosuppression is urgent and serology is positive. Treat norovirus supportively and control outbreaks with soap-and-water hygiene, bleach-based surface disinfection, and excluding symptomatic staff for at least forty-eight hours, because alcohol sanitizers underperform.   For the full chapter with MCQs, tables, and primary-guideline references, visit www.boardpearls.com. Questions or feedback: [email protected]. (00:00) - Introduction and exposure-based workup (00:35) - Suspecting parasites by exposure (01:14) - Giardia and its single-dose therapy (02:43) - Cryptosporidium and immune status (03:22) - Entamoeba histolytica two-stage therapy (04:41) - Strongyloides and the pre-steroid screen (07:32) - Norovirus and the outbreak pattern (09:34) - Rotavirus and the viral differential