Parasitic Infections of the Intestine

Study Notes

Giardia lambia: worldwide distribution, lives in the small intestine, causes malabsorption and diarrhea
Entamoeba histolytica: infects the colon, causes bloody diarrhea (amoebic dysentery) and amoebic liver abscess
Cryptosporidium parvum: more prevalent in immunocompromised individuals, causes diarrhea
Cyclospora cyatenensis: parasitizes the small intestinal mucosa, causes diarrhea for several weeks
E.bienusi: microsporidian that parasitizes the small intestine, more common in immunocompromised individuals, detected in the blood
Plasmodium: causes malaria, four species infect humans: P.falciparum, P.vivax, P.ovale, and P.malariae

B.coli: large motile ciliated parasite, lives in the colon of pigs, humans, and rodents, causes colonic ulceration
Strongyloides: inhabits the small bowel, infection more severe in immunosuppressed people (e.g. HIV/AIDS, malnutrition, intercurrent disease)
Enterobius (pinworm or threadworm): prevalent in cold and temperate climates, found mainly in children
Trichuris (whipworm): soil-transmitted helminth, prevalent in warm, humid conditions, causes diarrhea, rectal prolapse, and anemia in heavily-infected people
Ancylostoma and Necator (hookworms): major cause of anemia in the tropics
Ascaris (roundworm): found worldwide in conditions of poor hygiene, transmitted by the fecal-oral route, adult worms live in the small intestine, causes eosinophilia
Filariasis:
- Onchocerca volvulus: transmitted by the simulium black fly, causes visual impairment, blindness, and severe itching of the skin
- Wuchereria bancrofti: major causative agent of lymphatic filariasis
- Brugia malayi: causes lymphatic filariasis
Toxocara: world-wide infection of dogs and cats, human infection occurs by ingesting embryonated eggs from dog or cat feces, common in children, causes visceral larva migrans (VLM)

Taenia saginata: acquired by ingestion of contaminated, uncooked beef, worldwide, causes minimal symptoms
Taenia solium: acquired by ingestion of contaminated, uncooked pork, worldwide, causes cysticercosis (systemic disease where cysticerci encyst in muscles and the brain), may lead to epilepsy
Echinococcus granulosus (dog tapeworm) and Echinococcus multilocularis (rodent tapeworm): cause hydatid disease when ingested, larvae develop in human host, causing space-occupying lesions in several organs (e.g. liver, brain)