Persons with amebiasis may or may not manifest the disease. Symptoms, if any, include flatulence, alternating diarrhea and constipation, and abdominal cramps. In advanced cases, the patient may complain of fever, abdominal tenderness and passage of bloody, mucoid stools (frank dysentery). Dehydration is imminent. The patient is emaciated and possibly anemic from chronic infection and malnutrion. A large mass  (ameboma) may obliterate the intestines. 

Colonies of trophozoites can cause ulcers and perforate the intestinal wall, resulting in severe abdominal pain and peritonitis needing urgent medical intervention.

Extraintestinal amebiasis can cause suppurative infection of the liver parenchyma (abscess), fever, chills, sweating, general debility, nausea, vomiting, and pain in the upper right quadrant. Amebas may spread to other organs, including the lungs or brain, the skin, especially around the buttocks, genitals, or wounds from abdominal surgery or injury.

Complications of amebic colitis include ameboma, toxic megacolon, fulminant or necrotizing colitis, and rectovaginal fistula. Hepatic amebiasis or liver abscess may lead to intrapericardial, intrathoracic, or intraperitoneal rupture, with or without secondary bacterial infection; invasion of the pleural or pericardial cavity; and migration to the brain via blood route and development of brain abscess. Other complications include GI bleeding, bowel perforation, peritonitis, stricture formation, empysema and intussusception [11] [12].

• Fever

  A 41-year-old man presenting with lower abdominal pain, constipation, abdominal distention, fever (37.5 degrees C) and fatigue was evaluated, and a mass localized to the left lower abdomen was identified. [ncbi.nlm.nih.gov]

• Weight Loss

  Sweating, chills, weight loss, and fatigue may also be present. Diagnosis Medical diagnosis of amebiasis is extremely important. [thirdworldtraveler.com]

  Symptoms include stomach cramps, watery or bloody diarrhea and weight loss. You have successfully created a MyPHO account! Use MyPHO to save content relevant to you, take online courses and register for subscriptions. [publichealthontario.ca]

  Symptoms include: fever, cough, dull abdominal pain, nausea, diarrhea, ulcers, constipation, gas, hepatomegaly, cough, and weight loss. [web.stanford.edu]

  The mild form of amebiasis includes nausea (a feeling of sickness in the stomach), diarrhea (loose stool/poop), weight loss, stomach tenderness, and occasional fever. [health.ny.gov]

• Chills

  […] manifestations that may range from an asymptomatic state to amoebic colitis (violent abdominal pain, a painful contracted feeling around the anal sphincter, blood and mucus in the stools but without the presence of fever), or amoebic liver abscesses (fever, chills [orpha.net]

  Article Summary X Although amebiasis can resolve itself, if you’re experiencing symptoms such as fever or chills, bloody diarrhea, abdominal discomfort, or alternating constipation and diarrhea, consult your doctor for treatment to speed up recovery. [wikihow.com]

  Sweating, chills, weight loss, and fatigue may also be present. Diagnosis Medical diagnosis of amebiasis is extremely important. [thirdworldtraveler.com]

  More severe cases may experience fever, chills and/or diarrhea with blood or mucous. Amebiasis is spread by consuming contaminated food or water, or touching contaminated surfaces. It can also spread sexually through oral-anal contact. [simcoemuskokahealthstats.org]

  Severe cases have fever, chills and bloody or mucoid diarrhea. In some instances, the disease-causing organism (pathogen) can invade other parts of the body. [bccdc.ca]

• Malnutrition

  Reviewed here are the associations and interactions of malnutrition, IgA and interferon-gamma, human leukocyte antigen alleles, and parasite genotypes to the outcome of infection. [ncbi.nlm.nih.gov]

  […] spread: Through food or water contaminated with stools Through fertilizer made of human waste From person to person, particularly by contact with the mouth or rectal area of an infected person Risk factors for severe amebiasis include: Alcohol use Cancer Malnutrition [nlm.nih.gov]

• Anemia

  A case of amebic anemia in a 53-year-old Louisianian prompted us to report it, in order to create awareness of such cases occurring in the absence of foreign travel. [ncbi.nlm.nih.gov]

  Wasting of the body (emaciation) and anemia can occur in people with chronic infection. Sometimes large lumps (amebomas) may form inside the large intestine (colon). In some people, the amebas spread to the liver where they can cause an abscess. [msdmanuals.com]

  Emaciation as well as anemia can happen in individuals with long-lasting infection. Often a large bulge or ameboma can form and block the intestine. [byebyedoctor.com]

• Dry Cough

  A 53-year-old man presented with a dry cough and mild fever. Chest radiography revealed an abnormal solitary mass lesion in the right upper lung field. The clinical diagnosis was a bacterial lung abscess. [ncbi.nlm.nih.gov]

  Dry cough, chest pain and decreased breath may be due to pleuropulmonary extension of the inflammatory process in the lesions of the superior surface. Hepatomegaly is the most important physical sign in hepatic amebiasis. [scielo.br]

• Diarrhea

  The median duration of acute diarrhea was 5 (1-10) days in Group I and 4.5 (1-10) days in Group II (p 0.965). [ncbi.nlm.nih.gov]

  In some cases, it invades the colon wall, causing colitis, acute dysentery, or long-term (chronic) diarrhea. The infection can also spread through the bloodstream to the liver. In rare cases, it can spread to the lungs, brain, or other organs. [nlm.nih.gov]

  Entamoeba moshkovskii is associated with diarrhea in infants and causes diarrhea and colitis in mice. J Infect Dis 2012 ; 206 : 744 – 51. 10. [doi.org]

• Abdominal Pain

  After treatment, the median interval from admission to defervescence was 2 days, to normalization of white cell count 3 days, and to resolution of abdominal pain 4 days. [ncbi.nlm.nih.gov]

• Nausea

  KEYWORDS: Adverse reaction; Amebiasis; Metronidazole; Nausea [ncbi.nlm.nih.gov]

  The mild form of amebiasis includes nausea (a feeling of sickness in the stomach), diarrhea (loose stool/poop), weight loss, stomach tenderness, and occasional fever. [health.ny.gov]

  Complications of amebiasis may include: Liver abscess (collection of pus in the liver) Medicine side effects, including nausea Spread of the parasite through the blood to the liver, lungs, brain, or other organs Call your health care provider if you have [nlm.nih.gov]

  Symptoms include fever, sweats, chills, weakness, nausea, vomiting, weight loss, and pain or discomfort in the upper right part of the abdomen over the liver. Rarely, amebas spread to other organs (including the lungs or brain). [msdmanuals.com]

  The mild form of Amebiasis includes nausea, diarrhea, weight loss, abdominal tenderness and occasional fever. The symptoms may appear from a few days to a few months after exposure by usually within two to four weeks. [algomapublichealth.com]

• Abdominal Cramps

  The symptoms and signs include loose stools, mild abdominal cramping, frequent, watery, and/or bloody stools with severe abdominal cramping (termed amoebic dysentery) may occur, flatulence, appetite loss, and fatigue. [medicinenet.com]

  Mild symptoms may include: Abdominal cramps Diarrhea: passage of 3 to 8 semiformed stools per day, or passage of soft stools with mucus and occasional blood Fatigue Excessive gas Rectal pain while having a bowel movement ( tenesmus ) Unintentional weight [nlm.nih.gov]

  However, the most common symptoms are abdominal cramps and loose stools. More severe cases may experience fever, chills and/or diarrhea with blood or mucous. [simcoemuskokahealthstats.org]

  Additional symptoms may include fever, and abdominal cramping and pain. In severe cases, ulcers may form in the intestinal wall; the amebae gain access to the bloodstream and travel to the liver to form abscesses. [healthcentral.com]

• Tenesmus

  Mild symptoms may include: Abdominal cramps Diarrhea: passage of 3 to 8 semiformed stools per day, or passage of soft stools with mucus and occasional blood Fatigue Excessive gas Rectal pain while having a bowel movement ( tenesmus ) Unintentional weight [nlm.nih.gov]

  Persons with intestinal amebiasis (amebic colitis) generally have 1 to 3 weeks of increasingly severe diarrhea progressing to grossly bloody dysenteric stools with lower abdominal pain and tenesmus. Weight loss and fever may be present. [kflaph.ca]

  Symptoms of Amebiasis Diarrhea, possibly containing blood or mucus Rectal pain during bowel movements (tenesmus) Intestinal gas (excessive flatulence) Severe abdominal cramping and tenderness Excessive gas Loss of weight High fever Fatigue Nausea and [healthcommunities.com]

  Mild symptoms may include: Abdominal cramps Diarrhea: passage of 3 to 8 semiformed stools per day, or passage of soft stools with mucus and occasional blood Fatigue Excessive gas Rectal pain while having a bowel movement (tenesmus) Unintentional weight [medlineplus.gov]

• Hepatomegaly

  Amebiasis should be considered in the differential diagnosis of infants and children with hematochezia or hepatomegaly, especially in endemic areas. [ncbi.nlm.nih.gov]

  […] asymptomatic state to amoebic colitis (violent abdominal pain, a painful contracted feeling around the anal sphincter, blood and mucus in the stools but without the presence of fever), or amoebic liver abscesses (fever, chills, abdominal pain, weight loss, hepatomegaly [orpha.net]

  Hepatomegaly was seen. On auscultation, breath sounds were decreased in the right lower lung field along with presence of pleural rub. [scielo.br]

  Presentation of liver abscess may be acute with fever and abdominal pain, tachypnea, and liver tenderness and hepatomegaly, or chronic with weight loss, vague abdominal symptoms, and irritability. [meddean.luc.edu]

• Back Pain

  pain Liver: hepatomegaly Kidney: kidney stone (nephrolithiasis), complicated urinary tract infection Left low back pain Spleen Kidney: kidney stone (nephrolithiasis), complicated urinary tract infection Low back pain kidney pain (kidney stone, kidney [en.wikipedia.org]

The diagnosis of amebiasis requires collection of fecal sample from the patient for subsequent tests [13]. Microscopic examination may not always reveal the presence of the amebas (trophozoites and/or cysts). Two methods are currently available:

1. In vitro reaction of parasite protein (antigen) with specific antibody and
2. Polymerase chain reaction (PCR)

Molecular diagnostic technique to identify ameba's genetic material. PCR amplifies the ameba's genetic material when present and makes detection possible even with minute quantities of reagents. Both tests are sensitive and specific. Routine microscopy examination may require three to six repeat ed stool examinations and differential diagnosis of ameba species is difficult based on gross morphology.

Colonoscopy can reveal the presence of ulcers or other signs of infection in the large intestine. Tissue samples may be obtained for further evaluation.

Parasites may not be found in the stool in extraintestinal amebiasis. Appropriate diagnostic methods are ultrasonography, CT scan, or MRI, with serological test for anti-ameba antibodies to confirm liver abscess or infection in other sites. Given a strong index of suspicion, the physician may initiate treatment with an amebicidal drug and if the patient responds well, the disease is presumed to be amebiasis. 

• Hyponatremia

  Development of such fulminant course is found to be associated with various factors including male gender, age over 60 years, associated liver abscess, progressive abdominal pain, and signs of peritonitis, leukocytosis, hyponatremia, hypokalemia, and [casesjournal.biomedcentral.com]

• Entamoeba Histolytica

  Pleuropulmonary amebiasis is an uncommon complication of Entamoeba histolytica infection. It typically occurs in endemic regions including Central and South America, Africa and the Indian subcontinent. [ncbi.nlm.nih.gov]

  Entamoeba histolytica cyst. Image courtesy of Centers for Disease Control and Prevention. Entamoeba histolytica trophozoite. Image courtesy of Centers for Disease Control and Prevention. [emedicine.medscape.com]

• Colitis

  Patients were stratified as right-sided colitis and proctosigmoiditis. [ncbi.nlm.nih.gov]

• Colonic Ulcer

  It was only possible to reach the final diagnosis by history of fever and lower GI bleed, on investigations pyothorax right side, colonic ulcers on colonoscopy, positive serology, and above all response to metronidazole. [atmph.org]

  In the early stages the colonic ulcers have a narrow neck and thus appear as small nodules with a minute surface opening (5 mm in diameter). [histopathology-india.net]

  Ulcers. 61 Premkumar M...Joshi YK 31304698 2019 35 Biliary Peritonitis due to a Ruptured Amebic Liver Abscess Mimicking a Periampullary Tumor and Liver Metastases with the Elevation of CA 19-9 and CA 125: A Case Report. 61 Marin-Leiva J...Damian Bello [malacards.org]

  However, E. histolytica trophozoites obtained from clinical samples, including colonic ulcer biopsy, mainly consist of one cell type which is ingested red blood cells [ 1 ••]. [doi.org]

  Reason #5: Severe amebic disease is associated with high fatality Following ingestion, infective cysts transform to invasive trophozoites, which leads to the development of mucosal inflammation and colonic ulcers [34]. [journals.plos.org]

The current drug of choice for amebiasis is metronidazole or tinidazole [14], which kills the trophozoites in the intestine and other organs. Metronidazole is taken daily for several days, whereas tinidazole is given as a single large dose, with fewer side effects. Dehydrated patients are given fluids. Alcoholic drink is contraindicated since it may cause nausea, vomiting, flushing and headaches. These drugs are not to be taken by pregnant women.

Metronidazole and tinidazole do not kill ameba cysts that are in the large intestine. A second drug (such as diloxanide, paromomycin, or iodoquinol) is prescribed to eliminate the cysts, thus prevent a relapse. These drugs may be taken by asymptomatic individuals who are positive for cysts both for prophylaxis and for eliminating the source of contamination of the environment with the infective stage of the parasite.

Amebiasis is among the leading causes of morbidity in developing countries. Susceptibility to infection and fatality rates vary with age, nutritional status, immune status , and involvement of extraintestinal foci. Severity of amebiasis is more pronounced in young children, especially neonates; malnourished individuals; pregnant and postpartum women; those on corticosteroids and those with immune deficiencies and/or malignancies.

Treatment of intestinal amebiasis with appropriate drugs is straightforward but there is no immunity following previous infections nor guarantee against reinfections. Complete elimination of the intestinal forms can prevent the occurrence of extraintestinal amebiasis. Ninety percent (90%) of persons with intestinal amebiasis are asymptomatic and only 4-10% of them developed colitis or extraintestinal amebiasis after a one year follow-up period. 

Effective treatment with amebicidal drugs has kept mortality rates below 1% for patients with uncomplicated liver abscess. On the other hand, hepatic amebiasis can be complicated by intraperitoneal rupture in 2-7% of patients and higher mortality rates can result from this [2].

Amebiasis is infection with the protozoan parasite, Entamoeba histolytica, which has two clinical manifestations i.e., intestinal amebiasis  (colitis. diarrhea, dysentery) and extraintestinal amebiasis (liver abscess, pleuropulmonary, cardiac, and cerebral involvement).

Other species of Entamoeba are: E coli, E dispar, E moshkovskii, E polecki, E coli, and E hartmanni. These too reside in the human intestinal lumen as commensals (non-pathogenic) and should be differentiated from E histolytica as the only potentially pathogenic species. E dispar and E moshkovskii have been recovered from patients with gastrointestinal (GI) symptoms; however, their role in the pathogenesis of amebiasis remains to be verified.

E dispar and E histolytica are indistinguishable from each other by light microscopy. Molecular techniques have shown them as two different species, with E dispar being the commensal (as in patients with HIV infection) and E histolytica, the pathogenic species.

Co-infections with E histolytica and E dispar have been reported in many individuals, with E dispar being 10 times more common than E histolytica. In Brazil and Egypt, E dispar and E histolytica infections are equally prevalent [2]. In Western countries, E dispar has been isolated from 20%-30% of MSM (men having sex with other men).

Transmission of E histolytica is primarily through the ingestion of fecally contaminated food and water containing cysts, or through the hands of food handlers. Sexual transmission occurs via oral-anal practices (anilingus). Malnutrition, resulting in immune deficiency , is a risk factor in amebiasis [3].

Amebiasis in the United States is approximately 4% of the total population. Of these, only 10% of E histolytica infections are invasive, and only 1% of those positive for E histolytica by stool examination actually develop symptomatic amebiasis. Asymptomatic E dispar infection is 10 times more prevalent than E histolytica.

About 50 million cases of amebiasis due to E histolytica are reported each year, with 100,000 deaths worldwide. This is presumed to be an underestimation, representing as it is, the so-called tip of the iceberg, since only 10%-20% of infected individuals become symptomatic [4] [5]. Amebiasis is among the leading causes of morbidity in developing countries [6].

Infection with the protozoan parasite E histolytica is associated with  proteolysis, tissue damage and host-cell apoptosis in humans and presumably nonhuman primates. Ingested E histolytica cysts from contaminated food and water or oral-anal sex undergo excystation in the terminal ileum or colon. Each mature cyst can give rise to four highly motile trophozoites which will colonize the intestinal mucosa, causing tissue lysis and ulcerations. Meanwhile,  trophozoites may find their way in the bloodstream and migrate to the liver, lung, and other sites, causing further damage thereat. With physiological changes in conditions in the intestinal lumen, the amebas may transform into cysts that are excreted in the feces. Excreted cysts when ingested by the next susceptible host will initiate a new infectious cycle.

The trophozoite's ability to invade the colonic epithelium is facilitated by a 260-kd surface protein, galactose/N -acetylgalactosamine (GAL/GalNAc)–specific lectin, containing a 170-kd subunit and a 35-kd subunit [7] [8]. IgA antibody binds to this lectin receptor, killing the ameba thus, preventing reinfection [9].

Amebapores, which are peptides capable of forming pores in bimolecular lipid layers of cell membranes are responsible for cytolysis and apoptosis of the parasite. Trophozoite-induced apoptosis in liver abscess was observed with a non-Fas and non–tumor necrosis factor (TNF)-α1 receptor pathway in experimental animal models [10]. Amebapores can also induce apoptosis at sublytic concentrations.

Cysteine proteinases are involved in colonization of the gut and may amplify interleukin (IL)-1–mediated inflammation just as human IL-1–converting enzyme would cleave IL-1 precursor to its active form [11]. The anaphylatoxins C3a and C5a and immunoglobulins, IgA and IgG are likewise cleaved and inactivated by cysteine proteinases [12].

E histolytica is equipped with 100 putative transmembrane kinases (TMKs), of which there are 9 subgroups. EhTMKB1-9 is found in proliferating trophozoites and is induced by serum. This was shown to be involved in phagocytosis and virulence of E histolytica in amebic colitis. Thus, TMKs such as EhTMKB1-9 may serve as potential targets for future drug development.

• The only lasting control of amebiasis is in breaking the cycle of transmission through sanitary human waste disposal, keeping food and water free from contamination with infective cysts, and good personal hygiene practices especially among food handlers. Treat all infected persons with amebicidal drugs for both trophozoite and cystic forms of the parasite.
• Amebiasis vaccine is in the developmental stage, with prospective candidates in the pipeline, expected to be available soon.
• The choice of vaccine material and its efficacy in ensuring long-term protective immunity are important considerations both for clinical and public health applications [15].

Amebiasis is an infectious disease of the large intestine, liver and other organs that is caused by the protozoan parasite, Entamoeba histolytica [1]. The parasite undergoes two developmental stages, namely:

1. A motile, vegetative, and tissue-invasive form, trophozoite and
2. A dormant, infective form, cyst.

The infective stage or cyst is transmitted directly from one person to another, or through food and water. The trophozoite or vegetative stage invades the intestinal mucosa, causing diarrhea or fulminant dysentery in intestinal amebiasis. Involvement of the liver and other organs such as the skin or brain is called extra-intestinal amebiasis.

Affected persons may be asymptomatic or may experience a variety of clinical manifestations such as alternate diarrhea and constipation, abdominal tenderness, cramps, malaise, and fever. Asymptomatic persons may be cyst-passers that is, cysts are found in their stools. Cyst is the infective stage to man. Trophozoites are found in the stools of patients with diarrhea or dysentery. These are motile amebas, usually seen with ingested red blood cells under the microscope.

Diagnosis is by routine microscopic examination of fecal smears or liver aspirate, and if needed, colonoscopy or ultrasonography, and blood tests. Oral anti-trophozoite drugs are taken by patients with diarrhea or dysentery, with another amebicide to eliminate the cysts.

Amebiasis is common in areas where fecal contamination of food and water is rampant due to poor sanitation. These are in Africa, the Indian subcontinent, parts of Central and South America, and Asia. In the United States, there are cases among immigrants and sometimes in travelers who might have acquired the infection from developing countries.

Amebiasis is an infectious disease primarily of the intestines caused by the protozoan parasite, Entamoeba histolytica. The ameba can reside in the large intestine (colon) with other species of amebas as commensals without causing disease. When conditions permit as when the innate immunity of the human host is impaired, the parasite may invade the intestinal wall, cause ulcers or perforations, and manifest clinically as colitis, chronic diarrhea, or at its worst, acute dysentery.  

From the intestines the amebas can migrate via the blood route to the liver, causing liver abscess. In severe cases the lungs, brain, skin and other organs may become involved.

Infection with Entamoeba histolytica cysts is acquired from ingestion of ameba cysts from contaminated food or water, through the unwashed hands of food handlers, through oral-anal sex, or in some places, when human waste is used as fertilizer.  

Symptoms

The symptoms of amebiasis range from mild to severe. Mild symptoms are:

• Diarrhea: Passage of 3 to 8 semiformed stools per day, or passage of soft stools with mucus and occasional blood
• Abdominal cramps
• Fatigue
• Flatulence
• Painful and unproductive bowel movement (tenesmus)
• Weight loss

Severe symptoms include:

• Dysentery: Passage of bloody, mucoid stools more than 10 times a day
• Abdominal tenderness
• Vomiting
• Fever
• Emaciation
• Dehydration

Diagnosis

• Microscopic examination of Direct Fecal Smears for trophozoites and/or cysts, repeated over several days
• Serological examinations for ameba antigens using specific antibody especially for extraintestinal amebiasis
• Colonoscopy or sigmoidoscopy (internal examination of the lower large intestine) 
• Microscopic examinatiion of tissues from infected organs such as liver aspirate

Treatment

• Amebicidal drug, metronidazole (kills the trophozoites) for symptomatic case; other amebicide such as diloxanide, for asymptomatic case or cyst-passer 
• Supportive treatment and drugs to control  vomiting
• Drink plenty of fluids, water for dehydrated patients
• Antibiotics (if co-existing bacterial infection is suspected)

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4. Valenzuela O, Morán P, Gómez A, et al. Epidemiology of amoebic liver abscess in Mexico: the case of Sonora. Ann Trop Med Parasitol. 2007 Sep; 101(6):533-8.

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6. Stauffer W, Abd-Alla M, Ravdin JI. Prevalence and incidence of Entamoeba histolytica infection in South Africa and Egypt. Arch Med Res. 2006 Feb; 37(2):266-9.

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9. Haque R, Mondal D, Duggal P, et al. Entamoeba histolytica infection in children and protection from subsequent amebiasis. Infect Immun. 2006 Feb; 74(2):904-9.

10. Seydel KB, Stanley SL Jr. Entamoeba histolytica induces host cell death in amebic liver abscess by a non-Fas-dependent, non-tumor necrosis factor alpha-dependent pathway of apoptosis. Infect Immun. 1998 Jun; 66(6):2980-3.

11. Rao S, Solaymani-Mohammadi S, Petri WA Jr, et al. Hepatic amebiasis: a reminder of the complications. Curr Opin Pediatr. 2009 Feb; 21(1):145-9.

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15. Parija SC. Progress in the research on diagnosis and vaccines in amebiasis. Trop Parasitol. 2011 Jan; 1(1):4-8.