Amebiasis

From Anvita Health Wiki

Contents 1 Etiology 2 Pathology 3 Clinical-manifestations 4 Laboratory 5 Diagnostic-procedures 6 Radiology 7 Differential-diagnosis 8 Management 9 More General Terms 10 References

Etiology

• - infection with Entamoeba histolytica

Pathology

• infection generally acquired by ingestion of contaminated food
• 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
• 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 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

• spherical in shape
• measure 10-20 um in diameter (generally 12-15 um)
• precyst has single nucleus without refractile cyst wall
• mature cyst has 4 nuclei, each 1/6 the diameter of the cyst
• glycogen is generally diffuse
• chromotoid bodies: elongated bars

• 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

Differential-diagnosis

• infectious agents causing dysentery

• parasitic

• Giardia lamblia
• Cryptosporidia
• Isospora
• schistosomiasis

• bacterial

• Escherichia coli
• Campylobacter
• Salmonella
• Shigella
• Vibrio sp
• Yersinia
• tuberculosis

• viral gastroenteritis

• 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

• pyogenic abscess
• hepatocellular carcinoma
• echinococcal cyst

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)

• intestinal disease

• metronidazole ( Flagyl) 750 mg PO TID for 10 days
• tinidazole is unavailable in the US
• dehydroemetine (Mebadin) for severe disease (available from CDC)
• follow with intraluminal agent (i.e 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 (i.e 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

• protozoan infection
• enterocolitis (dysentery)

References

1. DeGowin & DeGowin's Diagnostic Examination, 6th edition, RL DeGowin (ed), McGraw Hill, NY 1994, pg 863
2. Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 1271-74
3. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 899-901
4. Medical Knowledge Self Assessment Program (MKSAP) 14, American College of Physicians, Philadelphia 2006

amebiasis