Snapshot A 26-year-old woman presents to the emergency room for large amounts of watery, nonbloody diarrhea, abdominal cramping, and lots of flatulence. She was trying to hydrate with water and sports drinks; however, she started feeling lightheaded and was brought to the hospital for treatment. She recently did a 5-day hike in Patagonia in South America. On physical exam, she demonstrated signs of dehydration but otherwise has no significant findings. Stool studies are sent and return with cysts on microscopy. (Giardia lamblia infection) Introduction Protozoa single-celled eukaryotes, often parasitic, that feed on organic tissues Infections of Protozoa Central Nervous System Gastrointestinal Visceral Infections Hematologic Infections Sexually Transmitted Diseases Toxoplasma gondii Naegleria fowleri Trypanosoma brucei Acanthamoeba Giardia lamblia Entamoeba histolytica Cryptosporidium Trypanosoma cruzi Leishmania donovani Plasmodium Babesia Trichomonas vaginalis Giardia lamblia Introduction clinical syndrome giardiasis demographics very common, especially in South America and Southeast Asia transmission ingestion of cysts in contaminated water pathogenesis only requires a few cysts to cause giardiasis risk factors camping and hiking poor sanitation IgA deficiencies Burton agammaglobulinemia common variable immunodeficiency selective IgA deficiency Presentation 1-2 weeks after exposure abdominal pain and bloating flatulence large-volume, watery, foul-smelling, fatty diarrhea Studies stool microscopy microscopy multinucleated trophozoites cysts stool antigen test Treatment metronidazole first-line if asymptomatic, patients may not need treatment unless they are at risk for severe disease (immunosuppression) paromomycin pregnant women Entamoeba histolytica Introduction clinical syndrome amebiasis hepatic abscess demographics tropical areas transmission ingestion of cysts in contaminated water fecal-oral risk factors poor sanitation pregnancy immunosuppression Presentation fever bloody or watery diarrhea right upper quadrant pain should raise suspicion for liver abscess Imaging abdominal computed tomography (CT) or ultrasound liver abscess Studies stool antigen test stool detection of DNA with polymerase chain reaction (PCR) stool microscopy trophozoites with ingested red blood cells in the cytoplasm cysts with multiple nuclei histology flask-shaped lesions Treatment metronidazole symptomatic patients paromomycin or iodoquinol asymptomatic patients with cysts detected in stool needle aspiration or percutaneous drainage of abscess liver abscess often has an “anchovy paste” or red-brown exudate Cryptosporidium Introduction clinical syndrome cryptosporidiosis transmission ingestion of oocysts in contaminated water fecal-oral risk factors immunosuppression HIV/AIDS Prevention filter all drinking water Presentation immunosuppressed patients severe and prolonged nonbloody diarrhea may be fatty weight loss immunocompetent patients mild watery diarrhea Studies acid-fast stain oocysts detection of antigen Treatment nitazoxanide immunocompetent patients Microsporidium Introduction clinical syndrome microsporidiosis transmission fecal-oral risk factors immunosuppression HIV/AIDs organ transplant Presentation weight loss nonbloody and watery diarrhea nausea and vomiting can also cause keratoconjunctivitis Studies stool detection of DNA with polymerase chain reaction (PCR) stool microscopy with trichrome stain ovoid spores with bright red walls gram-positive Treatment albendazole first-line topical fumagillin keratoconjunctivitis