Amebiasis is an infectious disease caused by the anaerobic protozoan Entamoeba histolytica. Transmission usually occurs via the fecal-oral route e. Depending on its manifestation, amebiasis is termed either intestinal or extraintestinal. After an incubation period of one to four weeks, symptoms such as loose stools with mucus and fresh blood in combination with painful defecation develop. In extraintestinal amebiasis, amebic abscesses mostly a single liver abscess in the right lobe of the liver may form, resulting in pain as well as a feeling of pressure in the right upper quadrant RUQ. Important diagnostic steps include stool analysis and liver ultrasound to assess extraintestinal amebiasis.
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Authors: Eric Houpt, M. Infection ranges from asymptomatic colonization of the large bowel to severe invasive intestinal and extra-intestinal disease. The parasite life cycle is relatively simple: humans orally ingest the cyst form from contaminated sources, excystation to the trophozoite form occurs in the small bowel, then the trophozoite either colonizes or invades the large bowel.
When the trophozoite encysts the life cycle is complete and the organism can be transmitted Serologic studies are more reliable, since only E. In a retrospective review of medical records of more than 34, HIV-infected patients in the U. The onset of acute rectocolitis is usually gradual over 1 to 3 weeks.
Most patients have abdominal pain, tenderness, watery or bloody diarrhea while only one third are febrile. Most patients have heme-positive stools, but fecal leukocytes may not be present.
Patients typically appear very ill and have fever, profuse bloody mucoid diarrhea, diffuse abdominal pain, and hypotensive with signs of peritoneal irritation. Intestinal perforation usually manifests as a slow leakage rather than an acute event.
Surgical intervention is indicated for bowel perforation or patients with no response to antiamebic therapy although attempts to suture such necrotic bowels are usually unsuccessful. Toxic megacolon is also rare 0. S ome report a syndrome of intermittent diarrhea, abdominal pain, flatulence, and weight loss for months in patients with amebas in the stool and positive for antiamebic serologic tests.
However a trial of therapy is certainly reasonable, as is ruling out inflammatory bowel disease, since amebiasis may worsen if corticosteroids begun. Ameboma is the formation of annular colonic granulation tissue at a single or multiple sites. It usually involves the cecum or ascending colon, and may mimic carcinoma of the colon.
Perianal amebiasis may result from extension of severe bowel disease to the skin. Lesions can be ulcerative or condylomatous, enlarge slowly over weeks to months, and result in pain and bleeding. Am ebic liver abscess is the most common extraintestinal manifestation of amebiasis and is 10 times more common in adult men despite an approximately equal sex distribution of colonic amebic disease.
The acute symptoms include fever and a constant, dull, aching pain in the right upper quadrant or epigastrium while a subacute course may present with prominent weight loss with less fever or abdominal pain. Hepatomegaly with point tenderness over the liver below the ribs or in the intercostals spaces is a typical finding.
Right-sided pleural pain or referred shoulder pain occurs when the diaphragmatic surface of the liver is involved. Patients with acute amebic liver abscess tend to have a normal alkaline phosphatase level and an elevated alanine aminotransferase level; the opposite is true for those with chronic disease. Ultrasonography, abdominal computed tomography, and magnetic resonance imaging are all excellent for detecting liver lesions but are not specific for amebic liver abscess.
P leuropulmonary amebiasis is the most common complication of amebic liver abscess. It occurs as a result of the rupture of a superior right lobe abscess with erosion through the diaphragm to involve the pleural space or lung parenchyma. Serous pleural effusion and atelectasis are common findings and do not indicate extension of disease. In addition, formation of a hepatobronchial fistula is not uncommon. Left lobe abscess are more likely to progress to rupture due to late clinical presentation.
Pericardial amebiasis, an unusual but serious complication, usually presents with fever and abdominal pain with progression to substantial chest pain and signs of congestive heart failure although acute perforation with cardiac tamponade and shock can occur.
Cerebral amebiasis has abrupt onset, and progresses rapidly to death over hours without adequate therapy. Thus, when patients with known amebiasis have alteration of mental states or focal signs, amebic brain abscess should be considered. Genitourinary amebiasis is rare and includes rectovaginal fistulas and vulvar lesions in women and penile amebiasis in men. There are presently several commercially available antigen kits for detecting Entamoeba TechLab E.
Stool PCR is a promising new technique. Performing isoenzyme analysis on trophozoites cultured from stool is another possible but laborious and impractical method. T he diagnosis of amebic colitis can be difficult to make.
When biopsy material is unavailable, another compatible finding is the presence of hematophagous trophozoites on stool microscopy see Figure 1. Amebic liver abscesses see Figure 3 are usually visible on ultrasound, CT scan, or hepatic scintiscan.
Liver enzymes can be normal or elevated. Serum antigen is becoming validated as a sensitive test as well, and has the distinct advantage of allowing one to follow therapy The gold standard for diagnosis is direct visualization or culture of trophozoites from the abscess; this is most successful when the tissue can be carefully obtained from the junction of the abscess and viable liver as during an open drainage procedure Material from percutaneously-obtained aspirates is usually of lower yield for microscopy or culture The serine-rich E.
Upon Entamoeba-cell co-culture experiments, cells undergo morphologic and DNA degradative changes consistent with apoptosis as well as necrosis The mechanism of apoptosis appears to involve direct activation of downstream caspases including caspase 3 When paired with the observation that IL-4 promotes infection persistence in mice 18 , a Th1-type immune response appears desirable.
There are at least three classes of drugs that have shown efficacy in clinical trials for asymptomatic intestinal colonization: dichloracetanilide derivatives, oral aminoglycosides, and 5-hydroxyquinolines.
The specific agents include diloxanide furoate Furamide , paromomycin Humatin , and iodoquinol Yodoxin, also known as diiodohydroxyquin see Table 2. All have a large worldwide experience. All have poor gastrointestinal absorption, which allows high luminal concentrations but renders them less effective in invasive disease. Because of rare optic toxicity and long duration of therapy with iodoquinol, and because in one recent study from Vietnam paromomycin was superior to diloxanide, paromomycin is our preferred agent 6.
Paromomycin has also been effective in a number of trials over the last 40 years. Many of these have shown cure rates for mild invasive disease as well E. Side effects with oral therapy are generally mild, but include diarrhea and other gastrointestinal disturbances and less commonly, headache and dizziness.
Therapy should be given with meals and for a full 7 or 10 days as failures have occurred with shorter courses. Newer studies have successfully used nitroimidazoles with longer half-lives namely tinidazole 17 , secnidazole 57 , and ornidazole for even shorter durations.
Tinidazole has had the most experience, is better tolerated than metronidazole, and can be administered for only days 5. The common side effects of metronidazole include nausea, headache, anorexia, and a metallic taste; less common ones include a disulfuram-like reaction to alcohol, vomiting, and peripheral neuropathy. The nitroimidazoles are rapidly absorbed after oral administration and are not effective against luminal trophozoites.
Therefore a course of treatment should be followed with a course of diloxanide or paromomycin. The metronidazole trials to date have been in "not severely ill patients". Regarding severe or "fulminant" amebic colitis there is no specific therapy recommendation. It is logical to assume that intravenous metronidazole would be effective in these patients, but data is limited to a case series from Japan that showed promise Based on old data the addition of parenteral emetine could be considered in refractory cases but data is lacking.
When patients fail medical treatment and undergo open surgery for acute abdomen, gastrointestinal bleeding, or toxic megacolon 64 , mortality is extremely high and broad-spectrum antibiotics should probably be added for bacterial spillage into the peritoneum. A promising new agent for intestinal amebiasis is nitazoxanide. The initial amebic colitis trials also included groups of "not severely ill patients" with amebic liver abscess.
Liver abscess was found to be in general more responsive than colitis, with cure in all patients regardless of the regimen. As with amebic colitis, after a course of therapy patients should receive a course of paromomycin.
Additionally, the use of dehydroemetine or chloroquine could be considered in severe or refractory cases. Nitazoxanide has not been studied in amebic liver abscess. Therapy is anecdotal, but would generally follow that of liver abscess, i. Clinical manifestations of invasive amebiasis among HIV-positive persons appear similar to those of HIV-negative persons and amebic liver abscess and colitis are the two most common presentations of invasive amebiasis.
In a study of 64 HIV-positive patients with 67 case of invasive amebiasis 52 amebic colitis, 40 amebic liver abscess, and 25 both , most of the patients become afebrile within 3 to 4 days after receipt of metronidazole despite moderate to severe immunosuppression; none of the patients died of invasive amebiasis Therefore, we would advise the conventional recommendations.
Of the drugs mentioned for asymptomatic infection, paromomycin has been used safely in pregnancy 31 and would be the drug of choice. For invasive intestinal disease, there is continued controversy over the use of metronidazole in pregnancy. There have been reports of facial defects and CNS tumors in children born from mothers taking metronidazole in the first trimester 67 but large analyses have simultaneously found no increased risk above controls 9.
Some would recommend a trial of paromomycin for mild invasive intestinal disease For severe colitis or liver abscess we feel that the risk of metronidazole to the fetus is less than that of the disease to the mother.
One could consider trying chloroquine for liver abscess since this drug has been used safely at lower doses in pregnant women for malaria prophylaxis, but we would again recommend metronidazole. D iloxanide furoate is a relative of chloramphenicol used since the s. The U. The drug is well tolerated, with only fourteen percent of patients reporting mild side effects, mainly flatulence or other gastrointestinal symptoms.
In the U. I odoquinol has been widely used for asymptomatic intestinal colonization because it is effective and inexpensive. However, there have been case reports of loss of vision 14 and several reports of myelo-optic neuropathy in patients taking the related drug iodochlorohydroxyquin We would thus consider it a second-line agent, though some may disagree.
A s far as alternative agents for amebic colitis, the tetracyclines can be used but they are not as effective as metronidazole Paromomycin and etophamide a dichloracetanilide have also been used successfully either alone or in combination It has often been used effectively inpatients failing metronidazole, and should be remembered in this situation.
It is reported to have no effect on amebic colitis. Extended courses have been recommended because relapses have historically been common, but these probably reflect the drug's ineffectiveness against intestinal parasites, and 20 days should be adequate if followed by a course of a luminal agent.
A nother potential alternative or addition to metronidazole for either colitis or liver abscess is emetine.
The problem is the drug is relatively unsafe owing to drug accumulation with cardiotoxicity and deaths have been reported. Bedrest and electrocardiogram monitoring is recommended. The drug must be given by subcutaneous or intramuscular injection.
Extra-intestinal Amebiasis: Clinical Presentation in a Non-Endemic Setting
Amebiasis is infection with Entamoeba histolytica. It is acquired by fecal-oral transmission. Infection is commonly asymptomatic, but symptoms ranging from mild diarrhea to severe dysentery may occur. Extraintestinal infections include liver abscesses.
Authors: Eric Houpt, M. Infection ranges from asymptomatic colonization of the large bowel to severe invasive intestinal and extra-intestinal disease. The parasite life cycle is relatively simple: humans orally ingest the cyst form from contaminated sources, excystation to the trophozoite form occurs in the small bowel, then the trophozoite either colonizes or invades the large bowel. When the trophozoite encysts the life cycle is complete and the organism can be transmitted Serologic studies are more reliable, since only E. In a retrospective review of medical records of more than 34, HIV-infected patients in the U.
Amoebiasis , also known amoebic dysentery , is an infection caused by any of the amoebae of the Entamoeba group. Cysts of Entamoeba can survive for up to a month in soil or for up to 45 minutes under fingernails. Prevention of amoebiasis is by improved sanitation , including separating food and water from faeces. Amoebiasis is present all over the world,  though most cases occur in the developing world. It is estimated that about 40, to , people worldwide die annually due to amoebiasis. Infections can sometimes last for years if there is no treatment.