Author:
Benjamin W.Osborne
Nicolas M.Monte
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
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 Prophylaxis |
| 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 mand ates workup for liver abscess or ameboma
- Digital rectal exam shows gross or occult blood in >70% of patients
Diagnostic Tests & 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 stand ard:
- 100% sensitive and specific
- Stool ELISA for E. histolytica-specific 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:
Diagnostic Procedures/Surgery
- 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)
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:
- 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 Prophylaxis |
- 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
- 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
- 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 Prophylaxis |
- Use metronidazole with caution in first trimester
- Erythromycin or nitazoxanide preferred
|
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
- 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-TapiaNC, Hernand ez-CallerosJ, Tellez-AvilaFI, et al. Image-guided percutaneous procedure plus metronidazole versus metronidazole alone for uncomplicated amoebic liver abscess . Cochrane Database Syst Rev. 2009;1:CD004886.
- EscobedoAA, AlmirallP, AlfonsoM, et al. Treatment of intestinal protozoan infections in children . Arch Dis Child. 2009;94:478-482.
- GonzalezMLM, DansLF, MartinezEG. Antiamoebic drugs for treating amoebic colitis . Cochrane Database Syst Rev. 2009;2:CD006085.
- HerediaRD, FonsecaJA, LópezMC. Entamoeba moshkovskii perspectives of a new agent to be considered in the diagnosis of amebiasis . Acta Trop. 2012;123(3):139-145.
- Mackey-LawrenceNM, PetriWA Jr. Amoebic dysentery . BMJ Clin Evid. 2011;2011:pii: 0918.
See Also (Topic, Algorithm, Electronic Media Element)