Amebiasis

Basics

Description

  • Invasive parasitic infection with both intestinal and extraintestinal manifestations
  • Endemic worldwide, especially developing areas with poor sanitation
  • Populations at risk:
    • Migrants and citizens from endemic regions (India, Africa, Mexico, tropical Central/South America)
    • Travelers with >1 mo stay in endemic areas
    • Institutionalized persons
    • Practitioners of oral–anal sexual activity
    • Men who have sex with men (MSM)
    • HIV-infected individuals
  • Risk factors for increased severity of disease and complications:
    • Immunocompromised: Corticosteroid use, HIV infection, malnutrition, malignancy
    • Pregnancy/postpartum state
    • Extremes of age

Etiology

  • Entamoeba histolytica, an anaerobic, nonflagellated protozoa causes most symptomatic infections
    • Entamoeba moshkovskii is an emerging species with increasing evidence of pathogenicity
    • Entamoeba dispar is 10× more common than E. histolytica but nonpathogenic. HIV+ patients often colonized, but no increased risk intestinal/extraintestinal disease
  • Fecal–oral transmission:
    • Humans are sole reservoir
  • Ingested organisms cause invasive colitis
  • Extraintestinal spread is hematogenous

Diagnosis

Signs and Symptoms

  • Intestinal disease:
    • Onset 1 wk–1 mo postexposure, often gradual
    • Acute diarrhea (nondysenteric colitis):
      • 80% of cases
      • Afebrile
      • Occult blood in stool
      • Benign abdominal exam
    • Classic dysentery:
      • Bloody mucoid diarrhea
      • Abdominal pain/benign abdominal exam
      • Tenesmus
      • Weight loss (50%)
      • Fever (38%)
    • Fulminant colitis:
      • Rare. Only 0.5% of cases
      • Toxic-appearing patient
      • Rigid abdomen (25%)
      • Fever
      • Severe bloody diarrhea
      • Can progress to bowel necrosis/perforation
      • >40% mortality if perforated
    • Toxic megacolon:
      • Toxic-appearing patient
      • Profuse diarrhea (>10 stools per day)
      • Fever
      • Distended, tympanitic abdomen with signs of peritonitis
      • Associated with corticosteroid use
      • High mortality
    • Ameboma:
      • Intraluminal granulation. Mimics colon CA
      • Tender palpable mass on exam
    • Amebic strictures:
      • Secondary to chronic inflammation/scarring
      • Crampy abdominal pain
      • Nausea and vomiting (may be feculent)
      • May cause partial or complete bowel obstruction
    • Chronic amebic colitis:
      • Mild recurrent episodes of diarrhea, abdominal cramping, and tenesmus
      • Weight loss occurs during episodes
      • May persist for years. Mimics IBD
  • Extraintestinal disease:
    • Amebic liver abscess:
      • Most frequent extraintestinal manifestation (3–9% of cases)
      • Single abscess in right lobe (50–80%)
      • May develop months to years postexposure (median of 3 mo)
      • Fever
      • Right upper quadrant pain
      • Hepatomegaly with point tenderness
      • Rales at right lung base
      • Concurrent diarrhea unusual (20–33%)
      • Complication: Rupture into pleural cavity (10–20%), peritoneum, or pericardium (rare)
      • Increased risk of rupture if >5 cm in diameter or left lobe location
    • Extrahepatic amebic abscess:
      • Brain
      • Lung
      • Perinephric
      • Splenic
      • Vaginal/cervical/uterine
    • Cutaneous amebiasis:
      • Rare. Presents on perineum and genitalia
      • Painful, irregularly shaped ulcers
      • Purulent exudate
      • May cause rectovaginal fistulae

Pediatric Considerations
Fulminant colitis is more likely


Pregnancy Considerations
Fulminant colitis is more likely

History
  • Possible sources of exposure
  • Membership in high-risk group
  • Travel to endemic area for >1 mo

Physical Exam
  • Identify evidence of peritonitis, sepsis, or shock
  • Tender abdominal mass mandates workup for liver abscess or ameboma
  • Digital rectal exam shows gross or occult blood in >70% of patients

Diagnostic Tests and Interpretation

Lab
  • CBC:
    • Leukocytosis common in amebic liver abscess and peritonitis
  • Alkaline phosphatase and ALT:
    • Elevated in amebic liver abscess
  • Serum electrolytes, BUN/creatinine if prolonged diarrhea or evidence of dehydration
  • Stool PCR is diagnostic gold standard:
    • 100% sensitive and specific
  • Stool ELISA for E. histolyticaspecific antigen:
    • 74–95% sensitive, 93–100% specific
  • Serum for anti–E. histolytica antibodies:
    • Essential if suspecting liver abscess. These patients rarely shed parasites in stool
    • 90–100% sensitive in amebic liver abscess
    • 70–90% sensitive in amebic colitis
  • Stool microscopy is <60% sensitive and no longer the test of choice
  • Fecal leukocytes and culture:
    • Rule out infection of enteroinvasive bacteria
    • Negative in amebiasis

Imaging
  • Abdominal US:
    • 58–90% sensitive for liver abscess
    • Sensitivity influenced by size and location
    • Allows rapid evaluation of abscess for increased risk of rupture (>5 cm or located in left lobe)
  • Abdominal CT or MRI:
    • Equivalent to US for delineating liver abscesses
    • Superior to US for detecting abscesses in other organs
  • Head CT or MRI:
    • Suspect amebic brain abscess if patient with known amebiasis has altered mental status or focal neurologic findings
    • Irregular nonenhancing lesions
  • CXR:
    • Elevated right hemidiaphragm and/or right pleural effusion in liver abscess

Diagnostic Procedures/Other
  • Colonoscopy with biopsy provides definitive diagnosis of amebic dysentery, colitis, ameboma, and amebic stricture
  • Percutaneous fine-needle aspiration of liver abscess to exclude bacterial abscess if nondiagnostic serology or antiamebic therapy fails
    • Not for primary treatment of liver abscesses

Differential Diagnosis

  • Intestinal amebiasis:
    • Enteroinvasive bacterial infection (Staphylococcus, E. coli, Shigella, Salmonella, Yersinia, Campylobacter)
    • Inflammatory bowel disease
    • Ischemic colitis
    • Arteriovenous malformation
    • Abdominal aortic aneurysm
    • Perforated duodenal ulcer
    • Intussusception, diverticulitis
    • Pancreatitis
    • Colorectal carcinoma
    • Appendicitis
  • Amebic abscess:
    • Bacterial abscess
    • Tuberculous cavity
    • Echinococcal cyst
    • Malignancy
    • Cholecystitis
  • Cutaneous amebiasis:
    • Carcinoma
    • STDs (condyloma acuminata, chancroid, syphilis)

Treatment

Initial Stabilization/Therapy

  • Airway, breathing, circulation (ABCs)
  • IV 0.9% NS if signs of significant shock

Ed Treatment/Procedures

  • Oral fluids if mild; IV if moderate/severe dehydration
  • Avoid antidiarrheal agents
  • Correct serum electrolyte imbalances
  • Stool sample for E. histolytica PCR or ELISA, plus serology for anti–E. histolytica antibodies
  • If stool or serum is positive for E. histolytica:
    • Metronidazole or tinidazole is first-line drug for systemic amebiasis (90% cure rate)
    • Chloroquine is an alternative systemic agent
    • Always follow systemic therapy with a luminal agent to eradicate intestinal colonization (erythromycin, iodoquinol, nitazoxanide, paromomycin, or tetracycline)
    • Do not use the luminal agents alone
  • If stool or serum is negative for E. histolytica:
    • Refer to gastroenterologist for colonoscopy with biopsy
    • Repeat serology in 7 days
    • Consider empiric course of metronidazole if high suspicion for amebiasis and patient is critically ill
  • If evidence of peritonitis or sepsis:
    • Add IV antibiotic directed against anaerobic and gram-negative bacteria
    • Surgical consult if toxic megacolon or perforation
  • If liver abscess is suspected:
    • US or CT of hepatobiliary system with concurrent amebic serology
    • If imaging demonstrates an abscess but serology is negative, treat with amebicides and repeat serology in 7 days
    • If symptoms do not improve after 5–7 days of empiric amebicidal therapy, consider fine-needle aspiration to rule out bacterial abscess or hepatoma
    • Consider abscess drainage by surgeon or interventional radiologist in conjunction with amebicidal therapy

Pregnancy Considerations
  • Use metronidazole with caution in first-trimester pregnancy, but do not withhold if patient has fulminant colitis or amebic abscess
  • Use erythromycin or nitazoxanide as intestinal amebicides along with metronidazole
  • Erythromycin or nitazoxanide may be used alone for mild dysentery in first-trimester pregnancy
  • Chloroquine, iodoquinol, paromomycin, tetracycline, and tinidazole are contraindicated

Medication

First Line Medication:
  • Metronidazole: 500–750 mg (peds: 35–50 mg/kg/24 hr) PO/IV q8h for 7–10 d
  • Tinidazole: 2 g daily (peds: 50 mg/kg/24 hr) PO for 3–5 d. For children older than 3 yr

Second Line Medication:
  • Chloroquine: 1 g PO daily for 2 d, then 500 mg PO daily for 14–21 d
  • Erythromycin: 250–500 mg (peds: 30–50 mg/kg/24 hr) PO q6h for 10–14 d
  • Iodoquinol: 650 mg (peds: 30–40 mg/kg/24 hr) PO q8h for 20 d
  • Nitazoxanide: 500 mg PO q12h for 3 d (10 d if liver abscess) for adults and children >12 yr
  • Paromomycin: 25–35 mg/kg/24 hr in 3 divided doses PO for 5–10 d
  • Tetracycline: 250–500 mg (peds >8 yr: 25–50 mg/kg/24 hr) PO q6h for 10 d

Pediatric Considerations
  • Tetracycline is avoided in children <8 yr given alternatives
  • Iodoquinol may cause more serious adverse effects when used in children at high doses for prolonged periods


Pregnancy Considerations
  • Use metronidazole with caution in first trimester
  • Erythromycin or nitazoxanide preferred

Ongoing Care

Disposition

Admission Criteria
  • Shock, sepsis, or peritonitis
  • Hypotension or tachycardia unresponsive to IV fluids
  • Children with >10% dehydration
  • Severe electrolyte imbalance
  • Patients unable to maintain adequate oral hydration:
    • Extremes of age, cognitive impairment, significant comorbid illness
  • Fulminant colitis or toxic megacolon
  • Bowel obstruction
  • Extraintestinal abscesses
  • Failure of outpatient regimen

Discharge Criteria
  • Nontoxic presentation of acute or chronic dysentery
  • Able to maintain adequate oral hydration and medication compliance
  • Dehydration responsive to IV fluids

Issues for Referral
Consult surgery if evidence of peritonitis, toxic megacolon, bowel necrosis, colonic perforation, or liver abscess

Follow-Up Recommendations

  • Gastroenterology and infectious disease follow-up in 7 d for repeat serology and possible endoscopic evaluation
  • Physical exam in 14 d to assess for treatment effectiveness and for development of complications or extraintestinal disease

Pearls and Pitfalls

  • Avoid antidiarrheal medications
  • Always give double therapy with both a systemic amebicidal (metronidazole, tinidazole, or chloroquine) PLUS an intestinal amebicidal (erythromycin, iodoquinol, nitazoxanide, paromomycin, or tetracycline) unless contraindicated
  • Always be vigilant for high-mortality complications such as fulminant colitis or extraintestinal disease

Additional Reading

  • American Academy of Pediatrics. Red Book 2018–2021 Report of the Committee of Infectious Diseases. 31st ed. Itasca, IL: American Academy of Pediatrics; 2018.
  • Chavez-Tapia NC, Hernandez-Calleros J, Tellez-Avila FI, et al. Image-guided percutaneous procedure plus metronidazole versus metronidazole alone for uncomplicated amoebic liver abscess. Cochrane Database Syst Rev. 2009;1:CD004886.
  • Escobedo AA, Almirall P, Alfonso M, et al. Treatment of intestinal protozoan infections in children. Arch Dis Child. 2009;94:478–482.
  • Gonzalez MLM, Dans LF, Martinez EG. Antiamoebic drugs for treating amoebic colitis. Cochrane Database Syst Rev. 2009;2:CD006085.
  • Heredia RD, Fonseca JA, López MC. Entamoeba moshkovskii perspectives of a new agent to be considered in the diagnosis of amebiasis. Acta Trop. 2012;123(3):139–145.
  • Mackey-Lawrence NM, Petri WA Jr. Amoebic dysentery. BMJ Clin Evid. 2011;2011:pii: 0918.

See Also

Authors

Benjamin W. Osborne
Nicolas M. Monte


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