Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 35-07: Amebiasis + Key Features Download Section PDF Listen +++ +++ Essentials of Diagnosis ++ Mild to moderate colitis with recurrent diarrhea Severe colitis: bloody diarrhea, fever, and abdominal pain, with potential progression to hemorrhage or perforation Hepatic abscess: fever, hepatomegaly, and abdominal pain +++ General Considerations ++ The Entamoeba complex contains three morphologically identical species E dispar, which is avirulent E moshkovskii, which is also avirulent E histolytica, which may be an avirulent intestinal commensal or lead to serious disease Humans are the only established host for E histolytica Transmission occurs through ingestion of cysts from fecally contaminated food or water Infection can be transmitted person-to-person Flies and other arthropods also serve as mechanical vectors Disease follows penetration of the intestinal wall, resulting in diarrhea, dysentery, and extraintestinal disease (see Amebic Liver Disease) +++ Demographics ++ E histolytica infections are present worldwide but are most prevalent in subtropical and tropical areas with crowded conditions, poor sanitation, and poor nutrition Urban outbreaks have occurred because of common-source water contamination Of 500 million persons worldwide infected with Entamoeba, most are infected with E dispar and an estimated 10% (50 million) are infected with E histolytica Mortality from invasive E histolytica is about 100,000 per year Severe disease is more common in Young children Pregnant women Persons who are malnourished Persons receiving corticosteroids + Clinical Findings Download Section PDF Listen +++ +++ Symptoms and Signs ++ In most infected persons, the organism lives as a commensal, and the carrier is without symptoms +++ Mild disease ++ Diarrhea may begin within a week of infection, although an incubation period of 2–4 weeks is more common Onset of abdominal pain and diarrhea is gradual Fever is uncommon Periods of remission and recurrence may last days to weeks or longer Abdominal examination may show Distention Tenderness Hyperperistalsis Hepatomegaly +++ Severe disease ++ Includes colitis and dysentery, with worse diarrhea (10–20 stools per day) and the appearance of bloody stools Physical findings of dysentery High fevers Prostration Vomiting Abdominal pain and tenderness Hepatic enlargement Hypotension Fulminant amebic colitis can progress to Necrotizing colitis Intestinal perforation Mucosal sloughing Severe hemorrhage Localized granulomatous lesions (amebomas) Can present after either dysentery or chronic intestinal infection Clinical findings include pain, obstructive symptoms, and hemorrhage and may suggest intestinal carcinoma +++ Differential Diagnosis ++ Inflammatory bowel disease Giardiasis, Shigella, Salmonella, Campylobacter Irritable bowel syndrome Lactase deficiency Cryptosporidiosis, cyclosporiasis Annular colonic carcinoma, tuberculosis, or lymphogranuloma venereum + Diagnosis Download Section PDF Listen +++ +++ Laboratory Tests ++ Diagnosis is typically made by identifying organisms in the stool Molecular diagnosis is possible from multi-pathogen panels, which are sensitive and specific, but expensive E histolytica and E dispar cannot be distinguished, but identification of amebic trophozoites or cysts in a symptomatic patient is highly suggestive of amebiasis Stool evaluation for organisms Not highly sensitive (~30–50% for amebic colitis) At least three stool specimens should be evaluated after concentration and staining Commercially available stool antigen tests (TechLab II, CELISA, QUIK CHEK) Can distinguish E histolytica from nonpathogenic species Offer improved sensitivity (> 90% for colitis) Multiple serologic assays are available These tests are fairly sensitive, although sensitivity is lower (~70% in colitis) early in illness They cannot distinguish recent and old disease Examination of fresh ulcer exudate for motile trophozoites and for E histolytica antigen may yield a diagnosis In mild disease, microscopic hematochezia is common In severe disease, leukocytosis and hematochezia, with fecal leukocytes not present in all cases +++ Diagnostic Procedures ++ Colonoscopy of uncleansed bowel In mild intestinal disease, shows no specific findings In severe disease, ulcers may be found with intact intervening friable mucosa, resembling inflammatory bowel disease + Treatment Download Section PDF Listen +++ +++ Medications ++ See Table 35–6 Asymptomatic infection with E dispar does not require therapy Intestinal colonization with E histolytica is treated with luminal agent Luminal agents Diloxanide furoate (500 mg three times daily with meals for 10 days) Iodoquinol (diiodohydroxyquin; 650 mg three times daily for 21 days) Paromomycin (30 mg/kg base, maximum 3 g, in three divided doses after meals daily for 7 days) Side effects Flatulence with diloxanide furoate Mild diarrhea with iodoquinol Gastrointestinal symptoms with paromomycin Relative contraindications Thyroid disease for iodoquinol Kidney disease for iodoquinol or paromomycin Metronidazole (750 mg three times daily for 10 days) or tinidazole (2 g once daily for 3–5 days) plus a luminal agent is treatment of choice Metronidazole Most commonly used in the United States However, tinidazole offers simpler dosing, a more rapid clinical response, and fewer side effects than metronidazole Side effects of both agents include Transient nausea Vomiting Epigastric discomfort Headache Metallic taste A disulfiram-like reaction may occur if alcohol is coingested Drug interactions with cimetidine, some anticoagulants, phenytoin, phenobarbital, lithium, and other drugs have been reported Should be avoided in pregnant or nursing mothers if possible Tetracycline (250–500 mg four times daily for 10 days) plus chloroquine (500 mg/d for 7 days) Alternative therapy Emetine or dehydroemetine can be given subcutaneously or intramuscularly in a dose of 1–1.5 mg/kg/day Maximum daily doses For emetine, 65 mg For dehydroemetine, 90 mg These agents only used until severe disease is controlled because they are cardiotoxic with a narrow therapeutic range Side effects include nausea, vomiting, pain at injection site Neither are available in the United States ++Table Graphic Jump LocationTable 35–6.Treatment of amebiasis.1View Table||Download (.pdf) Table 35–6. Treatment of amebiasis.1 Clinical Setting Drugs of Choice and Adult Dosage Alternative Drugs and Adult Dosage Asymptomatic intestinal infection Luminal agent: Diloxanide furoate,2 500 mg orally three times daily for 10 days or– Iodoquinol, 650 mg orally three times daily for 21 days or– Paromomycin, 10 mg/kg orally three times daily for 7 days Mild to moderate intestinal infection Metronidazole, 750 mg orally three times daily (or 500 mg intravenously every 6 hours) for 10 days or– Tinidazole, 2 g orally daily for 3 days plus– Luminal agent (see above) Luminal agent (see above) plus either– Tetracycline, 250 mg orally three times daily for 10 days or– Erythromycin, 500 mg orally four times daily for 10 days Severe intestinal infection Metronidazole, 750 mg orally three times daily (or 500 mg intravenously every 6 hours) for 10 days or– Tinidazole, 2 g orally daily for 5 days plus– Luminal agent (see above) Luminal agent (see above) plus either– Tetracycline, 250 mg orally three times daily for 10 days or– Dehydroemetine2 or emetine,2 1 mg/kg subcutaneously or intramuscularly for 3–5 days Hepatic abscess, ameboma, and other extraintestinal disease Metronidazole, 750 mg orally three times daily (or 500 mg intravenously every 6 hours) for 10 days or– Tinidazole, 2 g orally daily for 5 days plus– Luminal agent (see above) Dehydroemetine2 or emetine,2 1 mg/kg subcutaneously or intramuscularly for 8–10 days, followed by (liver abscess only) chloroquine, 500 mg orally twice daily for 2 days, then 500 mg daily for 21 days plus– Luminal agent (see above) 1See text for additional details and cautions.2Not available in the United States. +++ Surgery ++ Surgical management of acute complications of intestinal amebiasis is best avoided whenever possible +++ Therapeutic Procedures ++ Fluid and electrolyte replacement is important for patients with significant diarrhea + Outcome Download Section PDF Listen +++ +++ Follow-Up ++ Examine at least three stools at 2- to 3-day intervals, starting 2–4 weeks after the end of treatment Colonoscopy and reexamination of stools within 3 months may be indicated +++ Complications ++ See Amebic Liver Abscess Successful therapy of severe amebic colitis may be followed by postdysenteric colitis, with continued diarrhea without persistent infection More long-term complications of intestinal amebiasis include Chronic diarrhea with weight loss, which may last for months to years Bowel ulcerations Amebic appendicitis +++ Prognosis ++ Postdysenteric colitis generally resolves in weeks to months Mortality rate of fulminant amebic colitis is > 40% +++ Prevention ++ Safe water supplies; water can be Boiled Treated with iodine (0.5 mL tincture of iodine per liter for 20 min; cysts are resistant to standard concentrations of chlorine) Filtered Sanitary disposal of human feces Adequate cooking of food Protection of food from fly contamination Handwashing In endemic areas, avoidance of fruits and vegetables that cannot be cooked or peeled +++ When to Refer ++ Progressive colitis despite therapy +++ When to Admit ++ Severe colitis or hepatic abscess + References Download Section PDF Listen +++ + +Pandey S et al. Comparative study of tinidazole versus metronidazole in treatment of amebic liver abscess: a randomized control trial. Indian J Gastroenterol. 2018 May;37(3):196–201. [PubMed: 29948994] + +Saidin S et al. Update on laboratory diagnosis of amoebiasis. Eur J Clin Microbiol Infect Dis. 2019 Jan;38(1):15–38. [PubMed: 30255429] + +Shirley DT et al. A review of the global burden, new diagnostics, and current therapeutics for amebiasis. Open Forum Infect Dis. 2018 Jul 5;5(7):ofy161. [PubMed: 30046644]