amebiasis
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Etiology
-infection with Entamoeba histolytica
Epidemiology
- infection generally acquired by ingestion of contaminated food
- more common in developing countries where sanitation may be suboptimal
- one outbreak caused by a contaminated colonic irrigation machine
- cysts are ingested & transform into trophozoites in the intestine
- trophozoites proliferate by binary fission in the colon
- both cysts & trophozoites may be passed in the feces
- only mature cysts are infective
Pathology
- host defenses, previous exposure, diet & strain of E. histolytica influence severity of infection
Clinical manifestations
- acute manifestations (amebic dysentery)
- fulminant onset
- cramping abdominal pain
- diffuse abdominal tenderness
- bloody diarrhea
- tenesmus
- fever
- dehydration
- invasion of the intestinal mucosa (colon & terminal ileum) may lead to perforation & peritonitis
- chronic manifestations (amebic colitis)
- intermittent symptoms
- mild, crampy abdominal pain
- diarrhea containing mucus or blood
- fever
- tenderness of cecum & ascending colon during cramping
- liver tenderness (amebic hepatitis)
- friction rub with liver abscess (5% of symptomatic patients)
Laboratory
- stool antigen testing more sensitive than ova & parasites
- stool ova & parasites
- motile (trophozoites) or encysted organisms
- trophozoites
- measure 10-60 um
- commensal forms are generally 15-20 um
- invasive forms are generally > 20 um
- progressively motile on wet mounts with hyaline finger-like pseudopods
- unstained nucleus is not visible
- with invasive disease, some trophozoites may contain ingested erythrocytes (pathognomonic)
- both pathogenic & commensal forms may contain ingested bacteria in the cytoplasm
- stained specimens, peripheral nuclear chromatin is evenly distributed along nuclear membrane
- cysts
- serology for Entamoeba histolytica
- antibodies are present in both invasive & intestinal disease
- ELISA or EIA
- 90% of patients with amebic abscess are positive
- 70% of patients with intestinal disease are positive
- 10% of asymptomatic carriers are positive
- indirect hemagglutination (IHA) titers remain increased for years after invasive infection
- counterimmunoelectrophoresis (CIE) becomes negative after cure of invasive disease
- cultures are not widely used
- polymerase chain reaction (PCR)
- complete blood count (CBC)
- leukocytosis without eosinophilia
- mild anemia may be present
- serum alkaline phosphatase may be elevated with hepatic involvement
Diagnostic procedures
- flexible sigmoidoscopy
- ulcers of various depth with raised edges
- small hemorrhages
- hyperemia
- trophozoites on aspirate of mucosal lesions
- indicate invasive disease
- highest yield at ulcer edge
- fine needle aspiration of liver abscess
Radiology
- barium enema may show irregular distribution of barium in cecum & ascending colon
- computed tomography (CT), ultrasound or MRI of abdomen may show liver abscess
Complications
Differential diagnosis
- infectious agents causing dysentery
- other causes or dysentery
- diverticulitis
- irritable bowel syndrome
- regional enteritis
- malabsorption syndrome
- exacerbation of inflammatory bowel disease (see management)
- colon cancer
- lymphoma
- other causes of hepatic abscess
Management
- asymptomatic individual passing cysts in feces
- treatment recommended because subsequent tissue invasion may occur
- iodoquinol* (Yodoxin) 650 mg PO TID for 21 days
- paromomycin* (Humatin) 25-30 mg/kg divided TID for 7 days
- diloxanide furoate (Furamide) 500 mg TID for 10 days (available from CDC, if b & c not options)
- symptomatic intestinal disease
- metronidazole (Flagyl) 750 mg PO TID for 10 days
- tinidazole is alternative for parasitic clearance
- dehydroemetine (Mebadin) for severe disease (available from CDC)
- follow with intraluminal agent (iodoquinol, paromomycin) to eradicate cysts
- hepatic abscess
- metronidazole (Flagyl) 750 mg PO TID for 10 days
- dehydroemetine (Mebadin) followed by chloroquine is an alternative
- aspiration of abscess
- no improvement after 72 hours of therapy
- severe liver tenderness or swelling
- follow with intraluminal agent (iodoquinol, paromomycin) to eradicate cysts
- glucocorticoid therapy (for inflamatory bowel disease) will exacerbate amebiasis & may result in toxic megacolon
- diet
- avoid fecally contaminated food and water
- vegetables grown in endemic areas are often contaminated
- water must be boiled to eradicate organism
- vegetables should be cleaned with a detergent & soaked in vinegar or acetic acid for 10 minutes to eradicate cysts
- peel all fruit
- avoid sexual practices that promote fecal-oral spread
* intraluminal agent
More general terms
More specific terms
References
- ↑ DeGowin & DeGowin's Diagnostic Examination, 6th edition, RL DeGowin (ed), McGraw Hill, NY 1994, pg 863
- ↑ Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 1271-74
- ↑ Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 899-901
- ↑ Medical Knowledge Self Assessment Program (MKSAP) 14, 16, 17, 18. American College of Physicians, Philadelphia 2006, 2012, 2015, 2018.