entamoeba histolytica

Question 1

distribution and transmission

Answer 1

worldwide distribution 
50 million infected 
70,000 deaths per year 
>90% infection rate in some communities 
faecal oral spread 
disease of poor sanitation and poverty

Question 2

trophozoites

Answer 2

10-40um

active and can be invasive and haematophagous

Question 3

cysts

Answer 3

10-15um nucleus divides twice and fully infective cysts have 4 nuclei
can survive for several days or weeks in the environment but rapidly killed by drying, extremes of temp, chlorination, iodine, coagulation and sand filtration of water supply

Question 4

life cycle

Answer 4

mature cysts ingested
excystation
trophozoites
multiplication to more trophozoites or cysts which are then passed in faeces
encystation cues are unknown and excitation caused partly by pH change

Question 5

diagnosis

Answer 5

microscopy

immunoassays

Question 6

dispar

Answer 6

similar in appearance to non pathogenic E. dispar
distinguished using monoclonal antibody tests or pcr
indicates poor hygiene and sanitation

Question 7

infection

Answer 7

90% of infections are non invasive dispar

risk of invasion increased by diet, concurrent GI infection, pregnancy, malnutrition,
immunosuppression

Question 8

patterns of infection

Answer 8

asymptomatic
intestinal amoebiasis
extra intestinal amoebiasis

asymp more likely to pass on as formed stool more likely to harbour mature cysts

Question 9

pathology

Answer 9

ulceration - flask shaped ulcers in the colon mucosa

liver abscess - invasion of liver by hepatic portal vein

dysentery

Question 10

treatment

Answer 10

nitromidazoles - metronidazole, tinidazole, ornidazole
highly absorbed in gut so lumen conc falls below therapeutic levels

asymp and luminal treatment = paromomycin, idodquinol and diloxanide furoate - poorly absorbed in gut and mop up trophozoites in the lumen

when metronidazole is contraindicated - dehydroemetine and chloroquine