Amebiasis

Amebiasis: Excerpt from The 5-Minute Pediatric Consult

Jason Kim, MD

Amebiasis - BASICS

Amebiasis - description

Clinical syndromes associated with Entamoeba histolytica infection

Amebiasis - general prevention

• Treatment of drinking water
• Hand washing
• Appropriate disposal of human fecal waste
• Use of condoms
• Infection-control measures: Standard precautions are recommended for the hospitalized patient.

Amebiasis - epidemiology

• Spreads person to person via fecal–oral transmission
• Less common modes of transmission include food and water borne infection
• Sexual transmission can occur among men who have sex with men.

Amebiasis - incidence

Amebiasis accounts for 40–50 million cases of colitis worldwide and leads to 40,000–110,000 deaths annually.

Amebiasis - prevalence

• The estimated prevalence in the US is 4% although there have been no recent serosurveys in developed countries.
• Worldwide distribution involving an estimated 10% or more of the world’s population. Most common in tropical areas, with infection rates as high as 20–50%. The highest morbidity and mortality are seen in developing countries in Central America, South America, Africa, and Asia.

Amebiasis - risk factors

• The very young, the elderly, and patients with underlying immunosuppression or malnutrition are at highest risk for severe disease.
• Patients in whom the diagnosis should be considered include:
  • Immigrants from or travelers to endemic areas
  • Children with bloody stools or mucus in stools
  • Children with hepatic abscess
  • The febrile child with right upper quadrant pain and tenderness, abdominal pain, or discomfort
  • The child with hepatomegaly, typically without jaundice

Amebiasis - pathophysiology

• Fecal–oral transmission
• E. histolytica is excreted as cysts or trophozoites in the stool of infected patients.
• Ingested cysts are unaffected by gastric acid and become trophozoites that colonize and invade the colon.
• Amebae attach to epithelial cells via a galactose/N-acetylgalactosamine (Gal/GalNac) binding lectin. The parasite has the ability to lyse human epithelial cells, or kill by inducing apoptosis. Then cytokines and chemokines released attract neutrophils, macrophages, and lymphocytes. The host immune response contributes significantly to the reduction of epithelial integrity.
• Amebas then use cysteine protease to cleave extracellular matrix proteins to invade the submucosal layers.
• Amebas can then disseminate directly from the intestine to the liver in up to 10% of patients. Dissemination from the liver to the lung, heart, brain, and spleen has been described.
• The incubation period is typically 1–3 weeks but can range from a few days to months or years.

Amebiasis - etiology

• E. histolytica is nonflagellated protozoan parasite.
• Other species of the Entamoeba family are nonpathogenic, including the morphologically identical Entamoeba dispar.

Amebiasis - DIAGNOSIS

Amebiasis - signs & symptoms

• The most common clinical manifestation is intestinal amebiasis.
• Intestinal disease may be asymptomatic or have mild symptoms such as abdominal discomfort, flatulence, constipation, and occasionally diarrhea.
• Nondysenteric colitis is characterized by intermittent diarrhea and abdominal pain.
• Acute amebic colitis (dysenteric) is associated with grossly bloody stools with mucus, abdominal pain, and tenesmus.

Amebiasis - tests

The diagnosis of amebiasis depends on the recognition of typical symptoms and routine laboratory tests.

Amebiasis - lab

• CBC typically reveals a leukocytosis.
• Transaminases are often not elevated.
• Occult blood is detected in stool.
• Stool samples:
  • Isolation and visualization:
    • Serial stool samples, usually 3, are recommended.
    • Samples obtained within 1–2 hours of passage should be examined by wet mount and fixed in formalin and polyvinyl alcohol.
    • Serial stool samples are necessary since cysts may be shed intermittently. 3 serial stool samples will detect up to 70% of patients with amebic colitis and 50% of patients with hepatic abscess.
    • Stool samples should not be contaminated by urine, water, barium, enema substances, laxatives, or antibiotics, since these substances may destroy or interfere with identification of the trophozoites.
    • Microscopy has a sensitivity of <60% and specificity of 10–50% on a single sample.
  • Second generation stool antigen testing kits (commercially available) also have demonstrated excellent sensitivity and specificity comparable to real time PCR.
• Serology:
  • Serum antiamebic antibodies are considered an adjunct to diagnosis.
  • ~85% of patients with amebic dysentery and 99% of patients with liver amebiasis will have positive serology.

Amebiasis - imaging

• Ultrasound, CT, or MRI of the liver
• In patients with hepatic amebiasis, chest x-ray may reveal elevation of the right hemidiaphragm.

Amebiasis - diag proced-surgery

• Note: Amebae are difficult to visualize in abscess aspirates and substantial risk is associated with CT or ultrasound-guided procedures, including bleeding, peritonitis secondary to spillage of amebae, or rupture of echinococcal cysts.
• Colonoscopy

Amebiasis - pathological findings

• Identification of trophozoites or cysts in the stool
• Colonic or rectal mucosa visualized by colonoscopy reveals ulcerations, and amebae can often be found around these lesions.

Amebiasis - differencial diagnosis

The diagnosis is often missed in children because the disease is not included in the differential. Because it is not common in the US, amebiasis may initially be misdiagnosed as bacterial dysentery. Differential diagnosis includes the following:

• Infection:
  • Salmonella species
  • Shigella species
  • Campylobacter species
  • Yersinia species
  • Clostridium difficile
  • Escherichia coli (enteroinvasive and enterohemorrhagic)
  • Pyogenic abscess
  • Echinococcal cyst
• Inflammatory bowel disease:
  • Crohn disease
  • Ulcerative colitis
• Miscellaneous:
  • Ischemic colitis
  • Diverticulitis
  • Arteriovenous malformations
  • Hepatoma

Amebiasis - TREATMENT

Amebiasis - general measures

• The goal of treatment is the elimination of tissue-invading trophozoites and intestinal cysts.
• The choice of treatment regimens depends on the clinical presentation.
• Agents that are active against E. histolytica are divided into 2 categories: Drugs with activity against intraluminal amebae and drugs with activity against extraintestinal and invasive amebiasis.

Amebiasis - medication

Amebiasis - first line

• Asymptomatic intestinal amebiasis: Intraluminal agents:
  • Iodoquinol is the drug of choice. The recommended dosage is 30–40 mg/kg/d (maximum, 1,950 mg) PO in 3 divided doses for 20 days.
• Acute amebic colitis or extraintestinal amebiasis:
  • Metronidazole (a tissue active agent) 35–50 mg/kg/d PO in 3 divided doses for 10 days (maximum, 2,250 mg/d) plus a course of treatment with an intraluminal active agent (as above). ~1/3 of patients treated with metronidazole alone will relapse.

Amebiasis - second line

• Asymptomatic intestinal amebiasis:
  • Diloxanide furoate (Furamide) at doses of 20 mg/kg/d (maximum, 1,500 mg/d) PO in 3 divided doses or paromomycin, 25–35 mg/kg/d PO in 3 divided doses for 7 days.
• Acute amebic colitis or extraintestinal amebiasis:
  • One study has reported good efficacy using nitazoxanide in children; however, it was small and combined E. histolytica and E. dispar into one stratum.
  • However, nitazoxanide shows good activity in vitro against E. histolytica.

Amebiasis - surgery

Patients with large liver abscesses or who have failed medical therapy should be considered candidates for surgical or percutaneous drainage.

Amebiasis - FOLLOW UP

Amebiasis - prognosis

Clinical improvement is expected within 72 hours of initiation of therapy.

Amebiasis - complications

• Amebic liver abscess:
  • 2nd most common presentation of amebiasis, often not associated with amebic dysentery
• Ameboma:
  • Abdominal mass representing granulation tissue in the colon
• Extraintestinal manifestations of amebiasis are presumed to be a result of direct extension from liver abscesses. These include the following:
  • Pericarditis
  • Pleuropulmonary abscess or empyema
  • Bronchohepatic fistula
  • Genitourinary tract abscess
  • Cerebral abscess
  • Cutaneous amebiasis:
    • This is a rare finding in children, with ~10 cases reported in the literature.
  • Epidemiologic studies from countries with high prevalence of amebiasis show an association between amebic diarrhea and poor growth. The negative effect on growth was significantly more deleterious than diarrhea caused either by Giardia or Cryptosporidium.

Amebiasis - patient monitoring

• Follow-up stool examination is always necessary to ensure eradication of intestinal amebae.
• For amebic abscesses, drainage should be considered if response to medical therapy has not occurred in 4–5 days.

Amebiasis - bibliography

1. Haque R, Huston CD, Hughes M, et al. Amebiasis. N Engl J Med. 2003;348:1565–1573.
2. Mondal D, Petri WA, et al. Entamoeba histolytica associated diarrheal illness is negatively associated with the growth of preschool children: Evidence from a prospective study. Trans Royal Soc Trop Med Hyg. 2006;100:1032–1038.
Ravdin JI, Stauffer WM. Entamoeba histolytica (amebiasis). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases, vol. 2. 6th ed., Philadelphia: Churchill Livingstone; 2005:3097–3111.
3. Stauffer W, Ravdin JI. Entamoeba histolytica: An update. Curr Opin Infect Dis. 2003;16:479–485.
4. Tanyuksel M, Petri WA. Laboratory diagnosis of amebiasis. Clin Micr Rev. 2003;16:713–729.

Amebiasis - CODES

Amebiasis - icd9

• 006 Amebiasis
• V02.2 Amebiasis

Book Source Details

• Book Title: The 5-Minute Pediatric Consult
• Author(s): M. William Schwartz MD; et al.
• Year of Publication: 2008
• Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.

More About Amebiasis

• Back to disease: Amebiasis: Introduction
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: The 5-Minute Pediatric Consult Authors: M. William Schwartz MD; et al. Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7577-9

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