Amebiasis

Description of Medical Condition

Amebiasis is caused by the intestinal protozoan, Entamoeba histolytica. Infection results from ingestion of fecally contaminated food, such as garden vegetables or by direct fecal-oral transmission. Most persons are asymptomatic or have minimal diarrheal symptoms. In a few patients, invasive intestinal or extraintestinal (e.g., liver, and less commonly kidney, bladder, male or female genitalia, skin, lung, brain) infection results. Amebic abscess of the liver may develop during the acute attack or 1 -3 months later; symptoms may be abrupt or insidious. Entamoeba histolytica has been divided into ‘pathogenic” and “nonpathogenic” strains. The pathogenic strains commonly cause invasive infection while the noninvasive strains cause only asymptomatic intestinal infection. More recently, the nonpathogenic strains have been assigned to a separate species, E. dispar. Unfortunately, the species cannot be distinguished in a routine clinical laboratory.

System(s) affected: Gastrointestinal, Renal/Uro-logic, Reproductive, Skin/Exocrine, Nervous

Genetics: N/A

Incidence/Prevalence in USA: Probably <1% overall, but much higher in some risk groups, such as areas with large immigrant populations

Predominant age: All

Predominant sex: Male > Female; probably because of greater occupational exposure

Medical Symptoms and Signs of Disease

Noninvasive infection (up to 99%)
- Asymptomatic (90%)
- Mild diarrhea
- Abdominal discomfort
Invasive intestinal infection
- Abdominal pain and tenderness
- Rectal pain
- Diarrhea
- Bloody stools
- Fever (30%)
- Systemic toxicity
Extraintestinal infection
- Fever
- Systemic toxicity
- RUQ abdominal pain and tenderness
- Nausea and vomiting
- Diarrhea (50%)
- Hematuria, dysuria, urinary frequency and urgency

What Causes Disease?

Infection with Entamoeba histolytica is transmitted through contaminated food or water, or through person-to-person contact

Risk Factors

Low socioeconomic status
Institutional living
Male homosexuality
Invasive disease is more common in certain geographic locations, including some parts of Mexico, South Africa, and India

Diagnosis of Disease

Differential Diagnosis

Other infectious causes of colitis, including shigellosis. Campylobacter infection, pseudomembranous colitis, and occasionally salmonellosis or Yersinia infection
Noninfectious causes of colitis include ulcerative colitis. Crohn colitis and ischemic colitis
Hepatic amebiasis must be distinguished from pyogenic liver abscess or superinfection of amebic abscess

Laboratory

Stool for ova and parasites (unfortunately, the sensitivity of this exam is poor). Diarrheal stool should be examined immediately for trophozoites in addition to fixed stool specimens (repeated as necessary). In invasive intestinal infection, stools are bloody, but fecal leukocytes are usually absent.
Serologic tests (especially indirect hemagglutination [HA]), positive in 85% of colitis patients and most patients with extraintestinal disease. Serologic tests should be done in patients with idiopathic inflammatory bowel disease to rule out amebiasis.
In bladder infections-amoebae and/or cysts in urine
Liver enzymes and alkaline phosphatase may be elevated in hepatic disease

Drugs that may alter lab results: Many drugs interfere with stool exams

Disorders that may alter lab results: N/A

Pathological Findings

Colon biopsy
- Lysis of mucosal cells (flask ulcers)
- PAS-stained trophozoites
- Oneutrophils at the periphery
Liver biopsy
Onecrosis surrounded by a rim of trophozoites
Liver aspirate — red-brown material (anchovy paste)

Imaging

CT scan or ultrasound for hepatic infection

Diagnostic Procedures

Rectosigmoidoscopy with biopsy
Needle aspirate of hepatic lesions may be needed to rule out pyogenic infection or superinfection

Treatment (Medical Therapy)

Appropriate Health Care

Outpatient

General Measures

Fluids and nutrition
Electrolyte management

Surgical Measures

With severe amebic colitis, surgery may be necessary

Activity

In accordance with illness of patient

Diet

As tolerated

Patient Education

Avoid conditions of re-exposure

Medications (Drugs, Medicines)

Drug(s) of Choice

Noninvasive infection
- Diiodohydroxyquin [also called iodoquinol] 650 mg tid for 20 days
Invasive infection
- Metronidazole (Flagyl) 750 mg tid for 5-10 days, followed by a 20 day course of diiodohydroxyquin to eliminate intestinal carriage
- Tinidazole (Tindamax) 2 gm daily for 3 days with food for intestinal infection and 2 gm daily for 3-5 days for liver abscess

Contraindications:

Diiodohydroxyquin — use cautiously in patients with thyroid diseases. Contraindicated in hepatic or renal dysfunction. May cause optic neuritis or peripheral neuropathy.
Known allergy to given medication

Precautions: None of the agents are proven safe in pregnancy, but pregnant women with invasive disease should still be treated

Significant possible interactions:

Metronidazole-ethanol: disulfiram reaction

Alternative Drugs

Noninvasive infection
- Diloxanide 500 mg tid for 10 days
- Paromomycin 500 mg tid for 10 days
Invasive infection
- Dehydroemetine (as effective as metronidazole, but cardiotoxic) 1-1.5 mg/kg/day IM for 5 days
- Chloroquine (less effective) 600 mg base/day for 2 days, then 200 mg/day for 2-3 weeks. Children 10 mg/kg/day up to maximum of 300 mg/day.

Patient Monitoring

Patient signs and symptoms, stool for ova and parasite

Prevention / Avoidance

Avoid risk factors when possible

Possible Complications

Toxic megacolon with rupture
Rupture of hepatic abscess which may perforate into subphrenic space, right pleural cavity or other nearby organs
Bladder perforation, urethral strictures, vesicointestinal fistula

Expected Course / Prognosis

Untreated invasive amebiasis is frequently fatal. With treatment, improvement usually occurs within a few days. Some patients with amebic colitis have irritable bowel symptoms for weeks after successful treatment. Relapses possible.

Miscellaneous

Associated Conditions

N/A

Age-Related Factors

Pediatric: More severe in neonates

Geriatric: More severe in elderly

Others: More severe in patients on corticosteroids and other immunocompromised patients

Pregnancy

More severe in pregnancy. Most agents are avoided in pregnancy (especially first trimester) because of concerns of teratogenicity, but invasive disease must still be treated. Paromomycin is sometimes recommended for noninvasive disease because it is not absorbed. Infectious disease consultation should be obtained.

Synonyms

Amebic colitis
Amebic dysentery

International Classification of Diseases

006.0 Acute amebic dysentery without mention of abscess

006.3 Amebic liver abscess

006.4 Amebic lung abscess

006.5 Amebic brain abscess

006.6 Amebic skin ulceration

006.8 Amebic infection of other sites

006.9 Amebiasis, unspecified