AMEBIASIS

AMEBIASIS - Rodney D.Adam, MD
BASICS
DESCRIPTION
• 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; infection may be more severe in patients taking corticosteroids and other immunocompromised patients.
• 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.
• E. 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, Entamoeba dispar. Unfortunately, the species cannot be distinguished in a routine clinical laboratory.
• System(s) Affected: Gastrointestinal; Nervous; Renal/Urologic; Reproductive; Skin/Exocrine
• Synonym(s): Amebic colitis; Amebic dysentery
ALERT
Geriatric Considerations
More severe in elderly
Pediatric Considerations
More severe in neonates
Pregnancy Considerations
• 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.
GENERAL PREVENTION
Avoid risk factors when possible.
EPIDEMIOLOGY
• Predominant age: All
• Predominant sex: Male > Female; probably because of greater occupational exposure
Prevalence
Probably 1% overall, but much higher in some risk groups, such as areas with large immigrant populations
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.
ETIOLOGY
Infection with E. histolytica is transmitted through contaminated food or water or person-to-person contact.


DIAGNOSIS
SIGNS AND SYMPTOMS
History
• Noninvasive infection (up to 99%) (characteristic of E. dispar)
- 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
- Right upper quadrant abdominal pain and tenderness
- Nausea and vomiting
- Diarrhea (50%)
- Hematuria, dysuria, urinary frequency and urgency
TESTS
Lab (1)[B], (2)[A]
• 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), positive in 85% of patients with colitis 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.
Imaging
CT scan or ultrasound for hepatic infection
Diagnostic Procedures/Surgery
• Rectosigmoidoscopy with biopsy
• Needle aspirate of hepatic lesions may be needed to rule out pyogenic infection or superinfection.
Pathological Findings
• Colon biopsy
- Lysis of mucosal cells (flask ulcers)
- Periodic acid-Schiff-stained trophozoites
- Neutrophils at the periphery
• Liver biopsy
- Necrosis surrounded by a rim of trophozoites
• Liver aspirate
- Red-brown material (anchovy paste)
DIFFERENTIAL DIAGNOSIS
• Other infectious causes of colitis
- Shigellosis
- Campylobacter infection
- Pseudomembranous colitis
- Occasionally salmonellosis or Yersinia infection
• Noninfectious causes of colitis
- Ulcerative colitis
- Crohn colitis
- Ischemic colitis
• Hepatic amebiasis must be distinguished from pyogenic liver abscess or superinfection of amebic abscess.
TREATMENT
STABILIZATION
Outpatient treatment
GENERAL MEASURES
• Fluids and nutrition
• Electrolyte management
Diet
As tolerated
Activity
In accordance with illness of patient
MEDICATION (DRUGS) (1)[B]
First Line
• Noninvasive infection
- Diiodohydroxyquin (also called iodoquinol): 650 mg t.i.d. PO for 20 days
• Invasive infection
- Metronidazole (Flagyl): 750 mg t.i.d. PO for 5-10 days, followed by a 20-day course of diiodohydroxyquin to eliminate intestinal carriage
- Tinidazole (Tindamax) 2 g daily for 3 days with food for intestinal infection and 2 g 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 have been proven safe during pregnancy, but pregnant women with invasive disease should still be treated.
• Significant possible interactions
- Metronidazole and ethanol: Disulfiram reaction
Second Line
• Noninvasive infection
- Diloxanide 500 mg PO t.i.d. for 10 days
- Paromomycin 500 mg PO t.i.d. for 10 days
• Invasive infection
- Dehydroemetine (as effective as metronidazole, but cardiotoxic): 1-1.5 mg/kg/d IM for 5 days
- Chloroquine (less effective): 600 mg base/d PO for 2 days, then 200 mg/d PO for 2-3 weeks (pediatric dose: 10 mg/kg/d up to maximum of 300 mg/d)
SURGERY
With severe amebic colitis, surgery may be necessary for necrosis or perforation.
FOLLOW-UP
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
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
PATIENT MONITORING
• Patient signs and symptoms
• Stool for ova and parasite
REFERENCES
1. Haque R,Huston CD,Hughs M,Houpt E,Petri WA Jr. Amebiasis. N Engl Journ Med. 2003;348: 1565-1573.
2. Tanyuksel M,Petri WA Jr. Laboratory diagnosis of amebiasis. Clin Microbiol Rev.2003;16:713-729.