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June 8th micro notes(MB)

June 8th micro notes(MB) - Lecture 28 Intestinal Protozoan...

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Lecture 28: Intestinal Protozoan Parasites Protozoa: Single cells Reproduce asexually in human host Severity of disease does not depend on infecting dose Distantly related organisms cause similar diseases Intestinal protozoa: Giardiasis, Amebiasis, Cryptosporidiosis o Transmitted by fecal-oral route Involves ingestion of cysts in contaminated food or water o Exhibit life cycle consisting of cyst stage and tryphozoite stage o Cysts: have resistant wall Infective and excreted with feces Contains 4 nuclei Can survive in water o Cysts transform into trophozoites Metabolically active and usually motile Contains 2 nuclei (looking at you with eyes in the lab!) What causes disease Mechanism of Diarrhea: Normal gut absorption is mediated by molecules on microvilli of small intestinal epithelial cells (brush border) Intact epithelium maintains balance between absorption and secretion o aka NO diarrhea Diarrhea results from imbalance between gut absorption and secretion o Secretory diarrhea Increases Cl- secretion by intestinal crypt cells Factors: toxins and inflammatory mediators o Malabsorptive diarrhea Caused by damage to the brush border Dysentery is a type of diarrhea that is characterized by blood and mucus in the stool. o or combo of both Transmission: person to person o Dare care centers at risk o Sexually among MSM o Food handlers Giardiasis: Much more prevalent in developing countries (travelers exposed) High prevalence in day care centers Major water-borne enteric disease Lumenal, Non-invasive (Mucosal damage without invasion) No known toxin or conventional virulence factors Divided by binary fission Life cycle: (encystation) o Found in lumen of cells in the SI o Egg shaped cysts survive for months in ice cold water o When it enters hosts temperature rises and acid bath in stomach Causes parasite to awaken Cyst form saves the protozoa from the stomach acid o In the small intestine the cyst wall opens, flagella emerges trophozoites form (form that causes disease) o Trophozoites can differentiate back into cyst form before being excreted in the stool so it can live in the water again (ie encystation) Inhibiting encystation would block transmission of giardiasis Trophozoites o Half pear shaped, binucleated cell body o 8 flagella and ventral disk o Swims in a helical motion; attaches to IEC o No mitochondria Histologic characteristics: o Colonization occurs in upper SI o Histologically normal in most cases o Rare: duodenitis, mild villous shortening, moderate increase in IEL, granulocyte infiltration in the mucosa o Infects more men than women (3:2 ratio) Clinical features: (Malabsorption symptoms ) o Asymptomatic in 40-60% of infected people o Symptoms: abdominal pain, cramping, bloating, diarrhea, flatulence, malodorous stool, weight loss Rarely: fever and vomiting o Malabsorption, malnutrition, failure of children to thrive Host defenses o
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