Entamoeba histolytica

Background

Intestinal protozoan parasite within the genus Entamoeba
Microscopically distinguishable from the non-pathogenic E. dispar, E. moshkovskii, and E. bangladeshii

Amoebic diarrhea, with or without dysentery, is common
- About 15 to 30% of cases involve amoebic dysentery (with macroscopic or microscopic blood)
Typically a subacute onset over 3 to 4 weeks and abdominal pain
- However, can be up to months
Fever is rare, even in dysentery
In children, can lead to intussusception, perforation, and necrotizing colitis

Amoebic liver abscess is far more common in men than women, and rare in children
Symptoms progress over 2 to 4 weeks, with fever (80%) and abdominal pain (80%)
- Right upper quadrant tenderness (75%), weight loss (40%), diarrhea (15-35%), cough (10%), and jaundice (10-15%)
- The pain is typically a dull ache in the right upper quadrant or epigastrium
More likely to present with abdominal pain and right upper quadrant tenderness than pyogenic liver abscess

Metastatic infections are possible, most often from direct extension of a liver abscess
Most commonly spreads to chest, with empyema, bronchohepatic fistula, pericarditis
Cerebral disease is rare but can happen

Microscopically indistinguishable from the non-pathogenic E. dispar, so needs molecular tests to confirm diagnosis
On aspiration, the fluid is classically odorless, thick, yellow-brown liquid, described as "anchovy paste"

Either
- Metronidazole 750 mg p.o. tid for 5 to 10 days
- Tinidazole 2 g PO daily for 3-5 days
Followed by a luminal agent, as below

Either
- Metronidazole 750 mg PO tid for 10 days, or
- Tinidazole 2 g PO daily for 5 days
Followed by a luminal agent:
- Paramomycin 500 mg p.o. tid for 7 days
- Iodoquinol 650 mg p.o. tid for 20 days
- Diloxanide furoate 500 mg p.o. tid for 10 days
May need surgery or aspiration if the lesion is large or medication has failed