Intestinal ProtozoaGiardiaEntamoebaCryptosporidiumTransmissionFecal/oral:most commonly with water and MSMFecal/oral: most commonly in food and MSMFecal/Oral: most commonly waterand MSMDiagnosis•Microscopicexam of stool for cysts•ELISA•Histology is normal because giardiais non-invasive•Micrscopicexam of stool for cysts•Biospy: parasitesare found at the edges of visibledamage•Micrscopicexam for oocystin feces•ELISAfor antigen•PCR not yet fully developedEpidemiology•More common in developing countries•Most common cause of waterborne diarrhea outbreaks intheUS•10% of the world infected, only minority developsymptoms•3rdcause of death from parasitic disease•Higherrisk in developing countries•Originally zoonotic(sheep, cattle)ClinicalPresentation•Asymptomaticin 40-60% of infected•Symptoms: abdominal pain, cramping, bloating, diarrhea,flatulence, malodorous stool, weight loss•Can be asymptomatic•Acute amebic colitis :diarrhea, dysentery, abdominalpain, low back pain, fever, abdominal tenderness•Symptoms:waterydiarrhea, anorexia, weight loss•Self-limited in immunocompetenthostsCommon Features of Protozoan Parasites•Reproduce asexually within the human host such thatthe severity of disease does not depend on theinfecting dose•Cyst form has a resistant wall and is the infective form•Cysts transform to trophozoites, metabolically activeand motile forms of the protozoaSecretoryDiarrheaMalabsorptiveDiarrheaMechanismIncreasedCl-secretionby small intestinalcrypt cellsDamage to the brushborder epithelial cellsCausesToxinsInflammatorymediatorsAnything thatdamages the brushborderflatulence, malodorous stool, weight loss•Causes malabsorptionsyndromes: steatorrhea,disaccharidasedeficiency (lactase deficiency can persistafterwards), D-xylose/B12/Folatemalabsorption, protein-losing enteropathy, vitamin A deficiency•Malabsorptionis likely due to mucosal damagepain, low back pain, fever, abdominal tenderness•Fulminantcolitis•Ameboma•Extraintestinalsite of amoebiasis:liver abscess (tenderliver, fever, hepatomegaly, diarrhea, weight loss)PathogenesisNOTCLEAR!•Non-invasive•No known toxin or conventional virulence factor•Causes tissue damage by invading through IECs•Consumes RBCs•Induces formation of paristophorousvacuoleHost Defense•B lymphocytes (hypogammaglobulinemiacauses increasedincidence and severity of infections,but IgAdeficiency has noeffect)•T lymphocytes: probelmaticgiardiainfections in AIDS•Disease is worse in HIV patientsLife Cycle•Egg shaped cyst (4 nuclei) is responsiblefor transmission•Once ingested, high body temperature and low gastric pHawakens the parasite. Excystationoccurs in the small intestine•Trophozoite(2 nuclei, 4 pairs of flagella, helical motion)
