Amebiasis is caused by Entamoeba histolytica, a protozoan that is found worldwide (see Etiology).The highest prevalence of amebiasis is in developing countries where barriers between human feces and food and water supplies are inadequate (see Epidemiology).
Although most cases of amebiasis are asymptomatic, dysentery and invasive extraintestinal disease can occur. amebic liver abscess is the most common manifestation of invasive amebiasis, but other organs can also be involved, including pleuropulmonary, cardiac, cerebral, renal, genitourinary, and cutaneous sites. In developed countries, amebiasis primarily affects migrants from and travelers to endemic regions, men who have sex with men, and immunosuppressed or institutionalized individuals.
E histolytica is transmitted via ingestion of the cystic form (infective stage) of the protozoa. Viable in the environment for weeks to months, cysts can be found in fecally contaminated soil, fertilizer, or water or on the contaminated hands of food handlers. Fecal-oral transmission can also occur in the setting of anal sexual practices or direct rectal inoculation through colonic irrigation devices.
Excystation then occurs in the terminal ileum or colon, resulting in trophozoites (invasive form). The trophozoites can penetrate and invade the colonic mucosal barrier, leading to tissue destruction, secretory bloody diarrhea, and colitis resembling infalmatory bowel diesease In addition, the trophozoites can spread hematogenously via the portal circulation to the liver or even to more distant organs (see Pathophysiology).
E histolytica is capable of causing a spectrum of illnesses (see Presentation). Intestinal conditions resulting from E histolytica infection include the following:
- Asymptomatic infection
- Symptomatic noninvasive infection
- Acute proctocolitis (dysentery)
- Fulminant colitis with perforation
- Toxic megacolon
- Chronic nondysenteric colitis
- Ameboma
- Perianal ulceration
Extraintestinal conditions resulting from E histolytica infection include the following:
- Liver abscess
- Pleuropulmonary disease
- Peritonitis
- Pericarditis
- Brain abscess
- Genitourinary disease
Laboratory diagnosis of amebiasis is made by demonstrating the organism or by employing immunologic techniques. In addition to standard blood tests, other laboratory studies employed for diagnosis include microscopy, culture, serologic testing, and polymerase chain reaction (PCR) assay (see Workup).
Treatment of amebiasis includes pharmacologic therapy, surgical intervention, and preventive measures, as appropriate (see Treatment). Most individuals with amebiasis may be treated on an outpatient basis, though several clinical scenarios may favor inpatient care.
