Parasites of GI Tract

Entamoeba transmission

Fecal‑oral via contaminated food/water; person‑to‑person; common in immigrants, travelers, MSM.

Entamoeba life cycle

Ingest cyst → trophozoite in colon → invasion → cysts shed in stool.

Entamoeba clinical features

Dysentery (bloody diarrhea), fever, abdominal pain; flask‑shaped ulcers; liver abscess (“anchovy paste”).

Entamoeba treatment

Metronidazole for invasive disease + luminal agent (paromomycin or iodoquinol) to clear cysts.

Giardia transmission

Waterborne (streams, lakes), daycare, person‑to‑person, zoonotic (beavers, dogs, cats).

Giardia clinical features + diagnosis histo

Non‑inflammatory watery diarrhea, steatorrhea, bloating, flatulence, weight loss; no fever or blood. Trophozoite looks back at you, PCR

Giardia treatment

Metronidazole 7 days; prevention via water purification and hygiene.

Cryptosporidium transmission

Waterborne outbreaks (pools, water parks), daycare, cattle exposure; oocysts resistant to chlorination.

Cryptosporidium clinical features

Watery diarrhea, crampy abdominal pain; self‑limited in immunocompetent; severe chronic diarrhea in AIDS (up to 17 L/day).

Cyclospora transmission + Symptoms + Diagnosis + Treatment

Foodborne (raspberries, basil, snow peas, lettuce). Diarrhea. PCR. Treat with TMP/SMT

Isospora (Cystoisospora) region/people + Symptoms + Diagnosis + Treatment

Tropical regions; AIDS patients. Diarrhea. Not seen on PCR, need acid fast stool stain. Treat with TMP/SXT

Ascaris (Roundworm) transmission

Fecal‑oral ingestion of eggs from contaminated soil/food; common worldwide.

Ascaris (Roundworm) life cycle

Ingest egg → larvae to liver → lungs → coughed up → swallowed → adult in intestine.

Ascaris (Roundworm) clinical features

Lung phase: eosinophilic pneumonitis, cough, wheezing, SOB, fever; intestinal phase: abdominal pain, obstruction, biliary migration.

Ascaris (Roundworm) diagnosis

Stool O&P (eggs); adult worms may be passed or coughed up.

Enterobius (pinworm) transmission

Fecal‑oral; eggs laid on perianal skin; common in children/daycare.

Enterobius (pinworm) clinical features

Perianal itching at night; sleep disturbance.

Enterobius (pinworm) diagnosis

Scotch‑tape test.

Enterobius treatment

Mebendazole, albendazole, or pyrantel pamoate(can get this OTC); repeat in 2 weeks; treat household contacts.

Hookworm transmission

Skin penetration by larvae in contaminated soil; barefoot exposure.

Hookworm life cycle

Larvae penetrate skin → lungs → swallowed → adult in intestine.

Hookworm clinical features

Abd pain, Iron‑deficiency anemia, protein‑losing enteropathy, eosinophilia; cutaneous larva migrans.

Hookworm diagnosis

Stool O&P (eggs).

Hookworm treatment (same as pinworm)

Albendazole, mebendazole, pyrantel pamoate.

Cutaneous larva migrans clinical features + treatment

Serpiginous, pruritic rash. Topical thiabendazole.

Strongyloides transmission

Skin penetration; autoinfection allows lifelong infection.

Strongyloides clinical features

Larva currens rash, eosinophilia, diarrhea; hyperinfection in immunosuppressed → sepsis, high mortality.

Strongyloides treatment

Ivermectin.

Taenia clinical features

Intestinal infection usually mild; cysticercosis causes seizures, hydrocephalus.

Taenia treatment

Albendazole + praziquantel; steroids for neurocysticercosis.