d2: gastrointestinal protozoan diseases

what is amoebiasis?

intestinal disease caused by infectious amoebae

what organism causes amoebiasis? is it aerobic or anerobic?

Entamoeba

obligate anaerobe → makes it well-suited to live in the intestines of animals

what are the two forms Entamoeba are found in? how are each important to infection?

trophozoite: motile, active form inside hosts

cyst: dormant, hardy, inactive form in soil, water

• from fecal contamination

• can last for a long time in the outside environment

describe the steps of infection for amoebiasis

cysts are ingested in water, soil, or food contaminated by fecal material from infected individuals

Entamoeba cysts mature into trophozoites and colonize the intestines (2-4 weeks)

in 9/10 infections, Entamoeba harmlessly feeds off intestinal bacteria and food particles

• no symptoms, will just shed Entamoeba in their feces

what can Entamoeba occasionally do? what happens rarely?

occasionally, reach the intestinal surface and begin killing intestinal epithelia

more rarely, may invade the bloodstream and attack the liver/other tissues

what is amoebic dysentery?

symptoms:

mild infection: diarrhea, mild stomach cramping/pain

what are the symptoms for severe infections of amoebic dysentery?

dysentery (blood, mucus in the stool)

diarrhea

stomach cramps/pain

mild fever

how are the symptoms of amoebic dysentery different from bacterial dysentery?

mild fever

different from bacterial dysentery because the amoeba doesn’t have endotoxins → doesn’t cause as big of an inflammation response

how is amoebiasis diagnosed?

generally lower fever than most bacterial dysentery

fecal smears, look for amoeba (free-living or cysts)

• close relative, Entamoeba dispar, totally harmless

suspected cases confirmed with blood tests

how is amoebiasis treated?

antiprotozoals: metronidazole → attacks anaerobic organisms

hydration

what disease is caused by Giardia? is it an anaerobic or aerobic organism?

giardia

flagellated anaerobic protozoan

what are the two forms of Giardia?

trophozoite = motile, active form inside host

cyst = dormant, hardy form in the environment

how is Giardia transmitted?

cysts ingested from fecal contamination food or water

• can be passed human to human

• can also be zoonotic (Beaver fever) → infected animal is pooping in a water supply that people are consuming

where does Giardia infect? what does it do when it infects?

cysts mature into trophozoites and colonize the small intestine (non-invasive)

suction cup that allows it to stick to the intestinal wall

grow to large numbers → block absorption of fluids and nutrients

what are the symptoms of giardia?

~50% of infections have no symptoms

in those with symptoms:

• diarrhea

• stomach cramps

• fatigue, weight loss

• gas, bloating

• greasy, floating, foul-smelling stool

• fever is rare

usually self-limiting, 2-6 weeks

how is giardia diagnosed?

fecal smear may reveal cysts

difficult to spot, and not all stool samples have any → multiple samples

string test

what is the string test?

1. swallow gelatin capsule with string tied to it

2. allow capsule to pass into intestines

3. once capsule dissolves, pull string back out

4. examine string for giardia

what is the treatment for giardia?

antiprotozoals

hydration