Week 2: common parasitic infection of GI tract

Question 1

Describe the pathogenesis and life cycles of 3 species of intestinal parasitic protozoa common to the US: entamoeba

Answer 1

common species: Entamoeba histolytica, giardia lamblia, crystosporidium spp.
1. Entamoeba histolytica
-ameoba, fecal-oral transmission. ingestion of cysts from contaminated foods, soil, or water
-life cycle: eat cysts, excitation in small bowel, liberation of trophozoites, multiplication, formation and excretion of cysts (trophozoites can penetrate other tissues)
-dx: stool examination for trophozoites or cysts
for 2 and 3 see another card

Question 2

Describe the pathogenesis and life cycle of common tapeworms

Answer 2

• cysticerci in not well cooked beef or pork eaten by human
• scolex attaches to mucosa of small intestines. Grows into mature adult
• proglottids in feces which develop into embryo
• cystercercosis can result from auto infection by vomiting or regurg of proglottids

Question 3

name 4 species of GI parasitic roundworms

Answer 3

• enterobius vermicularis (pinworm)
• ascaris lumbricoides (roundworm)
• necator americanus (hookworm)
• ancylostoma duodenale (hookworm)
• trichuris trichiura (whipworm)
• trichinella spialis (porkworm)
• strongyloides stercoralis (threadworm)

Question 4

Describe diagnostic methods used in the laboratory to detect parasitic infections of the GI tract

Answer 4

-O&P exam: microscopic eval to look for parasites in stool

Question 5

Describe guardia lamblia and cryptosporidium spp.

Answer 5

2. Giardia lamblia
   - most often responsible for water-related outbreaks of diarrheal illness.
   - ingestion of cysts from contaminated waters. not killed by chlorination.
   - Fecal oral. anal/oral. life cycle similar to above
3. Cryptosporidium spp.
   - -1-3% in US. in Surface watrers: water parks, pools. oocysts resistant to chlorine, filtration may not be enough.
   - oocysts ingested. excyst in upper GI, release sporozoites. oocysts excreted in feces.

Question 6

Enterobius vermicularis (Pinworm)

Answer 6

• most common nematode infection in US
• mostly in children, daycare centers
• oral/fecal route transmission. larvae hatch in small intestines. Females migrate to perianal region at night to lay eggs.
• Dx: scotch tape test

Question 7

Ascaris lumbricoides (roundworm)

Answer 7

• most common worm infection in the world

- high incidence in Asia

Question 8

hookworms -necator americanus and ancylostoma duodenale

Answer 8

• warm moist soil
• larva penetrates skin of human (foot usually). enters blood stream, reaches lungs, developmental stage. migrates up trachea to esophagus, is swallowed. in intestines, larva develops into adult worms.
• blood suckers. chronic anemia, growth retardation in children.