Amebiasis (Entamoeba histolytica Infection)

  • Medical Author:
    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

  • Medical Editor: Jerry R. Balentine, DO, FACEP
    Jerry R. Balentine, DO, FACEP

    Jerry R. Balentine, DO, FACEP

    Dr. Balentine received his undergraduate degree from McDaniel College in Westminster, Maryland. He attended medical school at the Philadelphia College of Osteopathic Medicine graduating in1983. He completed his internship at St. Joseph's Hospital in Philadelphia and his Emergency Medicine residency at Lincoln Medical and Mental Health Center in the Bronx, where he served as chief resident.

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Amebiasis facts

  • Amebiasis is a disease caused by infection with a parasitic amoeba that, when symptomatic, can cause dysentery and invasive extraintestinal problems.
  • The cause of amebiasis is mainly the protozoan parasite Entamoeba histolytica.
  • Some risk factors for amebiasis include consuming contaminated food or water, association with food handlers whose hands are contaminated, contact with contaminated medical devices such as colonic irrigation devices, and being pregnant.
  • Amebiasis is contagious and maybe contagious for weeks to many years if untreated.
  • Only about 10%-20% of infected individuals show symptoms and signs. The symptoms and signs include
  • Amebiasis is diagnosed from your medical and travel history and from testing stool samples for the presence of E. histolytica cysts; other tests may also be included such as liver function tests.
  • Some asymptomatic infections are not treated; others may be treated with medications that work to eliminate the parasite from inside the intestines or within the tissues.
  • Surgical treatment infrequently may be required to remove large abscesses or if certain other complications such as gastrointestinal bleeding, perforation of the intestinal tract, or toxic megacolon occurs.
  • It is possible to prevent amebiasis by avoiding contaminated food and/or water, good sanitation techniques, and avoidance of contaminated food handlers and other carriers of the parasite. There is a vaccine available for animals, and researchers are working on a vaccine for humans.
  • The prognosis for most patients infected with amebiasis is good, however, if complications develop, the prognosis begins to drop.

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Amebiasis Symptom

Abdominal pain

Abdominal pain is caused by inflammation of an organ (for example, appendicitis, diverticulitis, colitis), by stretching or distention of an organ (for example, obstruction of the intestine, blockage of a bile duct by gallstones, swelling of the liver with hepatitis), or by loss of the supply of blood to an organ (for example, ischemic colitis).

To complicate matters, however, abdominal pain also can occur without inflammation, distention or loss of blood supply. An important example of the latter is the irritable bowel syndrome (IBS). It is not clear what causes the belly pain in IBS, but it is believed to be due either to abnormal contractions of the intestinal muscles (for example, spasm) or abnormally sensitive nerves within the intestines that give rise to painful sensations inappropriately (visceral hyper-sensitivity).

What is amebiasis?

Amebiasis is a parasitic disease (also known as amebic or amoebic dysentery and/or amoebiasis) caused by infection with Entamoeba histolytica or another amoeba (for example, E. dispar); the disease may be asymptomatic in most individuals. E. histolytica is the species that produces symptoms only in about 10% of those infected. The organism usually produces dysentery and invasive extra intestinal problems, the most common of which are liver abscesses, although other organs can be involved. The disease is most common in people who live in tropical areas with poor sanitation. It is estimated that amebiasis causes 50,000-100,000 deaths worldwide each year.

What causes amebiasis?

The cause of amebiasis is infection by the protozoan parasite Entamoeba histolytica; it begins when the cystic form (infective stage) is ingested when the person drinks contaminated water or eats contaminated foods, comes in contact with contaminated colonic irrigation devices or the contaminated hands of food handlers, or by anal sexual practices.

The cystic form changes into trophozoites (invasive form) in the ilium or colon and invade the mucosal barrier, leading to tissue destruction and diarrhea. These trophozoites can reach the portal blood circulation to the liver and eventually go to other organs.

What are risk factors for amebiasis?

Risk factors include

  • drinking contaminated water,
  • eating contaminated foods,
  • association with food handlers whose hands are contaminated,
  • anal sexual practices,
  • contaminated medical devices such as colonic irrigation devices,
  • malnourishment,
  • recipients of corticosteroids,
  • pregnancy,
  • very young patients, and
  • travelers to endemic areas such as Southeast Asia or Central America.

What is the incubation period for amebiasis?

The incubation period for amebiasis is variable. Symptoms begin to appear in about one to four weeks after ingestion of the cysts; however, the range may be from a few days to years.

Is amebiasis contagious? If so, what is the contagious period for amebiasis?

Yes, amebiasis is contagious person to person. It is spread by the fecal-oral route. The contagious period lasts as long as the infected patient excretes cysts in their stools. Consequently, the contagious period may last for weeks to many years if untreated.

What are amebiasis symptoms and signs?

Although only about 10%-20% of people infected with the parasites become ill, those individuals may produce the following symptoms and signs:

  • Early symptoms (in about one to four weeks) include loose stools and mild abdominal cramping
  • If the disease progresses, frequent, watery, and/or bloody stools with severe abdominal cramping (termed amoebic dysentery) may occur.
  • If the trophozoites reach the intestinal walls and go through them, symptoms of liver infection such as liver tenderness and fever are the initial signs and symptoms of liver abscess formation (hepatic amebiasis).
  • Other organs (heart, lungs, brain, for example) may produce symptoms specific to the organ and produce severe illness and/or death.
  • Abdominal tenderness
  • Tenesmus
  • Flatulence
  • Appetite loss
  • Weight loss
  • Fatigue
  • Anemia
  • Occasionally cause skin lesions (cutaneous amebiasis)

What specialists treat amebiasis?

In addition to your primary care physician, the following specialists may be consulted:

  • Gastroenterologist
  • Infectious disease specialist
  • General surgeon (especially if the patient develops severe disease like fulminant colitis)
  • Occasionally, dermatologist

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What tests do health care professionals use to diagnose amebiasis?

If your recent health history and travel history suggests a possibility of amebiasis, your doctor may ask you to provide several stool samples to screen for the presence of E. histolytica cysts in your stools. In addition, some routine blood tests as well as other tests to determine if parasites spread to other organs may be initiated. These tests may include the following:

What are medical treatment options for amebiasis?

Asymptomatic infections are not treated unless they are occurring in non-endemic areas. If patients are shedding E. histolytica cysts, the following luminal agents (drugs that work on cysts that are not invading the gastrointestinal epithelium) are as follows:

To treat invasive amebiasis, metronidazole (Flagyl, Metrogel, Noritate) is recommended even for amoebic liver abscesses (up to 10 cm sized abscesses). Tinidazole (Tindamax) is FDA approved for treatment of both intestinal or extraintestinal (invasive) amebiasis. Other countries have similar drugs for treatments, but they are not available in the United States.

Amoebic colitis can be treated with nitroimidazoles, but they should be followed up by a luminal agent.

Treatment of hepatic amebiasis has been successful in some patients with chloroquine (Aralen) or dehydroemetine (which is only available from the CDC and is not a preferred treatment because of potential heart toxicity).

If the gastrointestinal tract is suspected to be perforated (perforation can occur with fulminant amoebic colitis), broad-spectrum antibiotics may be used to prevent peritonitis.

What are surgical treatment options for amebiasis?

Surgical treatments are required or indicated for amebiasis treatment due to the following:

  • Gastrointestinal bleeding (massive or uncontrolled)
  • Perforated amoebic colitis
  • Toxic megacolon
  • Failure to respond to metronidazole after four days of treatment
  • Amoebic liver abscesses greater than 10 cm in size
  • Empyema after the liver abscess rupture
  • Amoebic liver abscess representing risk of rupture to the pericardium
  • Impending abscess rupture (no medical response in about three to five days to expanding abscess)
  • Percutaneous drainage by catheter can be lifesaving in patients with amoebic pericarditis

Are there home remedies for amebiasis?

There are many home remedies for amebiasis available on the Internet. They range from increased fluid intake, coconut water, buttermilk, black tea, and herbal tea to garlic, Indian lilac, oregano, and apple cider vinegar. If you think you have amebiasis, you should discuss your symptoms with a doctor before trying remedies.

What are complications of amebiasis?

Although infrequent, there can be serious complications of the disease. They include

  • liver abscesses,
  • lung abscesses,
  • brain abscesses,
  • ameboma (a large local lesion of the bowel caused by the response to the infecting parasite),
  • fulminant or necrotizing colitis,
  • rectal rational fistula,
  • bloody dysentery,
  • toxic megacolon,
  • increased risk for cancer, and
  • death.

Is it possible to prevent amebiasis?

Yes, amebiasis can be prevented by stopping the fecal contamination of food and water by correcting poor sanitation. Identification and treatment of food handlers or other carriers of the parasite can reduce the chance of getting food-borne amebiasis. Avoiding sexual practices that involve fecal-oral contact also may reduce the chance of getting the disease. Avoiding malnutrition and alcohol use can reduce risk of the disease.

Gal-lectin, an antigen from the parasite, has been used as a vaccine to protect animals against intestinal amebiasis and against amoebic liver abscesses. Other parasitic components are being tried as possible vaccine components to use in humans. Unfortunately, amebiasis doesn't result in any long-term immunity so that individuals can be reinfected multiple times.

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What is the prognosis of amebiasis? What is the recovery time for amebiasis?

In general, the prognosis of amebiasis is good since the vast majority of infected individuals showed little or no symptoms. However, if complications develop such as abscesses, peritonitis, or toxic megacolon, the prognosis may vary from fair to poor depending on the availability of medical support services.

Recovery time for amebiasis is related to the severity of the disease. If a person has no symptoms, there is no recovery time. Recovery time after medical treatment varies from about one to two weeks to as many as four weeks or more after surgery. You and your doctor need to discuss your estimated recovery time once treatment begins.

REFERENCE:

Dhawan, V. "Amebiasis." Medscape. June 22, 2017. <http://emedicine.medscape.com/article/212029-overview>.

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Reviewed on 10/6/2017
References
REFERENCE:

Dhawan, V. "Amebiasis." Medscape. June 22, 2017. <http://emedicine.medscape.com/article/212029-overview>.

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