Description

Amebiasis is caused by the protozoan parasite Entamoeba histolytica (1). Infection is acquired by the fecal-oral route, either directly by person-to-person contact or indirectly by eating or drinking fecally contaminated food or water (1,2).

Occurrence

Amebiasis occurs worldwide but is more common in areas of poor sanitation and nutrition, particularly in the tropics (2). The majority of E. histolytica infections, morbidity, and mortality occurs in Africa, Asia, and Central and South America (1,3). Approximately 50 million cases of invasive E. histolytica disease occur each year, with up to 100,000 deaths (2,4). However, only an estimated 10%-20% of infected individuals become symptomatic (2). The prevalence of asymptomatic E. histolytica infection varies geographically. Reports of E. histolytica prevalence rates as determined by enzyme-linked immunosorbent assay (ELISA) or polymerase chain reaction (PCR) tests on stool from asymptomatic persons in developing countries range from 1% to 21% (5). The prevalence and presentation of symptomatic amebiasis also vary geographically. For example, a study in Bangladesh indicated that preschool children experienced 0.09 episodes of E. histolytica-associated diarrhea and 0.03 episodes of amebic dysentery each year (6). A study in Hue City, Vietnam, reported that the annual incidence of amebic liver abscess was at least 21 per 100,000 inhabitants (7). Comparisons of E. histolytica infection in Egypt and South Africa have shown that amebic colitis is the predominant presentation in Egypt, whereas amebic liver abscesses predominate in South Africa (8).

Risk for Travelers

Travelers to developing countries are at low but definite risk for E. histolytica infection (1). Data on travelers returning from the developing world were collected from 30 specialized travel or tropical-medicine clinics on six continents. The rate of acute amebic diarrhea ranged from 1.5% in travelers returning from Southeast Asia to 3.6% in those returning from Central America. The overall rate in this selected group of travelers returning from all regions was 2.7% (9). Other studies among travelers to the tropics provide similar estimates (10,11).

During an outbreak of amebiasis and giardiasis among 160 Italian tourists visiting Thailand on an organized tour, 72.4% acquired E. histolytica infections and 10.6% developed amebic abscesses or colitis. In this outbreak, amebiasis and giardiasis were associated with consumption of drinks with ice, ice cream, and raw fruit in ice (12). Studies among residents in Brazil (13) and Ecuador (14) have similarly identified water (inadequately chlorinated drinking water) and food (ingestion of raw vegetables) as risk factors for infection, in addition to failure to wash hands before eating and lower socioeconomic status. In general, the risk of infection for both travelers and residents is highest in areas of poverty and in settings with poor sanitation where barriers between human feces, food, and water are inadequate (5).

Clinical Presentation

The clinical spectrum of amebiasis ranges from asymptomatic infection to fulminant colitis and peritonitis to extraintestinal amebiasis (1). The incubation period is commonly 2-4 weeks but ranges from a few days to years (15). The parasite initially infects the colon, and diarrhea is the most common symptom (2). The diarrhea can worsen to painful, bloody bowel movements, with or without fever (amebic dysentery) (1). Occasionally, the parasite may spread to other organs, most commonly the liver (amebic liver abscess). Entamoeba dispar, a nonpathogenic ameba that also inhabits the colon, cannot be distinguished from the pathogen E. histolytica by routine microscopy (1). An enzyme immunoassay kit to specifically detect E. histolytica in fresh stool specimens is commercially available. Polymerase chain reaction (PCR)-based diagnostic tests have been developed but are not widely available (16).

Prevention

No vaccine is available. Travelers to developing countries should be advised to follow the precautions detailed in the Risks from Food and Drink section in Chapter 2 and to avoid sexual practices that may lead to fecal-oral transmission.

Treatment

Travelers may be advised to consult with an infectious disease specialist to ensure proper diagnosis and treatment. Iodoquinol or paromomycin are the drugs of choice for asymptomatic but proven E. histolytica infections. For symptomatic intestinal infection and extraintestinal disease (e.g., liver abscess), treatment with metronidazole or tinidazole should be immediately followed by treatment with paromomycin or iodoquinol (17). E. dispar infection does not require treatment (1).

References

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2. Ravdin JI, Stauffer WM. Entamoeba histolytica (amoebiasis). In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, PA: Churchill Livingstone; 2005. p. 3097-111.
3. Petri WA Jr, Singh U. Diagnosis and management of amoebiasis. Clin Infect Dis. 1999;29:1117-25.
4. World Health Organization. Amoebiasis. Wkly Epidemiol Rec. 1997;72:97-100.
5. Stanley SL Jr. Amoebiasis. Lancet. 2003;361:1025-34.
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7. Blessmann J, Le Van A, Tannich E. Epidemiology and treatment of amoebiasis in Hue, Vietnam. Arch Med Res. 2006;37:270-2.
8. Stauffer W, Abd-Alla M, Ravdin JI. Prevalence and incidence of Entamoeba histolytica infection in South Africa and Egypt. Arch Med Res. 2006;37:266-9.
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10. Weinke T, Friedrich-Janicke B, Hopp P, Janitschke K. Prevalence and clinical importance of Entamoeba histolytica in two high-risk groups: travelers returning from the tropics and male homosexuals. J Infect Dis. 1990;161:1029-31.
11. Ansart S, Perez L, Vergely O, Danis M, Bricaire F, Caumes E. Illnesses in travelers returning from the tropics: a prospective study of 622 patients. J Travel Med. 2005;12:312-8.
12. de Lalla F, Rinaldi E, Santoro D, Nicolin R, Tramarin A. Outbreak of Entamoeba histolytica and Giardia lamblia infections in travellers returning from the tropics. Infection. 1992;20:78-82.
13. Benetton ML, Goncalves AV, Meneghini ME, Silva EF, Carneiro M. Risk factors for infection by Entamoeba histolytica/E. dispar complex: an epidemiological study conducted in outpatient clinics in the city of Manaus, Amazon Region, Brazil. Trans R Soc Trop Med Hyg. 2005;99:532-40.
14. Rinne S, Rodas EJ, Galer-Unti R, Glickman N, Glickman LT. Prevalence and risk factors for protozoan and nematode infections among children in an Ecuadorian highland community. Trans R Soc Trop Med Hyg. 2005;99:585-92.
15. Heymann DL, editor. Amoebiasis. In: Control of Communicable Diseases. 18th ed. Washington, DC: American Public Health Association; 2004. p. 11-5.
16. Tanyuksel M, Petri WA Jr. Laboratory diagnosis of amoebiasis. Clin Microbiol Rev. 2003;16:713-29.
17. Abramowicz M, editor. Drugs for Parasitic Infections. In: The Medical Letter. New Rochelle, NY: The Medical Letter; 2004. p. 1.