Amebiasis

Key Features

Essentials of Diagnosis

• Acute dysentery: diarrhea with blood and mucus, abdominal pain, tenesmus

  or

• Chronic nondysenteric diarrhea

  or

• Hepatic abscess

• Amoebas or cysts in stool or abscesses; amebic antigen in stool

• Serologic evidence of amebic infection

General Considerations

• Defined as an infection with Entamoeba histolytica regardless of symptoms

• E histolytica is found worldwide but has a particularly high prevalence in areas with poor sanitation and socioeconomic conditions

• In the United States, infections are seen in travelers to and emigrants from endemic areas

• Most infections are asymptomatic (> 90%), but tissue invasion can result in amebic colitis, hepatic abscess, and hematogenous spread to other organs

• Transmission is usually fecal-oral

Clinical Findings

Symptoms and Signs

• Intestinal amebiasis

  • Asymptomatic cyst passage

  • Acute amebic proctocolitis

  • Chronic nondysenteric colitis

  • Ameboma

• Acute amebic colitis

  • Typically, there is a 1- to 2-week history of loose stools containing blood and mucus, abdominal pain, and tenesmus

  • Some patients are febrile or dehydrated

  • Pain over the lower abdomen

• Chronic amebic colitis

  • Causes recurrent episodes of bloody diarrhea over a period of years

  • Clinically indistinguishable from idiopathic inflammatory bowel disease

• Ameboma

  • Localized amebic infection, usually in the cecum or ascending colon

  • Presents as a painful abdominal mass

• Amebic liver abscess

  • Typically presents with acute fever and right upper quadrant tenderness

  • Pain may be dull, pleuritic, or referred to the right shoulder

  • Physical examination reveals liver enlargement in less than 50% of affected patients

  • Subacute presentation lasting 2 weeks to 6 months may be seen in some patients

    • Hepatomegaly, anemia, and weight loss are common findings

    • Fever is less common

Differential Diagnosis

• Acute amebic colitis should be distinguished from other causes of dysentery

  • Bacterial (eg, Salmonella spp, Shigella spp, E coli spp, Campylobacter spp)

  • Parastitic (eg, Schistosoma mansoni, Balantidium coli)

  • Noninfectious (eg, inflammatory bowel disease, diverticulitis, ischemic colitis)

• Chronic amebic colitis has to be distinguished from

  • Inflammatory bowel disease

  • Cyclospora

• Liver abscess must be distinguished from echinococcal hydatid cyst

Diagnosis

Laboratory Findings

• ELISA assays are positive in approximately 95% of patients with extraintestinal amebiasis, 70% with intestinal E histolytica disease, and 10% of asymptomatic patients shedding E histolytica cysts

• However, these antibodies persist for years, and a positive result does not distinguish between acute and past infection

• Polymerase chain reaction (PCR)–based testing has the highest sensitivity and specificity for the diagnosis of E histolytica

Imaging

• Ultrasonography and CT scanning

  • Sensitive techniques to detect hepatic abscesses

  • Can be used to guide fine-needle aspiration to obtain specimens for definitive diagnosis

• Because an amebic abscess may take up to 2 years to completely resolve on CT scans, imaging techniques are not recommended for therapeutic evaluation

Diagnostic ...