 Two morphologically identical but genetically distinct species of Entamoeba commonly infect humans. 1-Entamoeba dispar, the more prevalent species 2-E. histolytica, the pathogenic species can become invasive Infection is established by ingestion of parasite cysts.

 Cysts are resistant to environmental conditions such as low temperature and the concentrations of chlorine commonly used  can be killed by heating to 55°C  cyst, which is resistant to gastric acidity and digestive enzymes →excysts in the small intestine to form 8 trophozoites →colonize the lumen of the large intestine and may invade the mucosal lining.

 Food or drink contaminated with Entamoeba cysts and direct fecal-oral contact are the most common means of infection  Untreated water and human feces used as fertilizer are important sources of infection.

 range from asymptomatic cyst passage to amebic colitis, amebic dysentery, ameboma, and extraintestinal disease. . E. histolytica infection is asymptomatic in about 90% of persons, but it has the potential to become invasive and should be treated  Severe disease is more common in young children, pregnant women, malnourished  Extraintestinal disease usually involves only the liver, but rare extraintestinal manifestations include amebic brain abscess, pleuropulmonary disease, ulcerative skin, and genitourinary lesions.

 occur within 2 wk of infection or be delayed for months colicky abdominal pains Diarrhea  Stools are blood stained and contain a fair amount of mucus with few leukocytes  fever documented in only ⅓ of patients  incidence is strikingly high in children 1–5 yr of age  amebic dysentery is associated with sudden onset of fever, chills, and severe diarrhea

 is uncommon in children.  Amebic liver abscess may occur months to years after exposure.  In children, fever is the hallmark and is frequently associated with abdominal pain, distention, and enlargement and tenderness of the liver.

 unremarkable in uncomplicated amebic colitis  in amebic liver abscess :leukocytosis, moderate anemia, high erythrocyte sedimentation rate, and elevations of hepatic enzyme (particularly alkaline phosphatase) levels. Stool examination negative results in >50% of patients with documented amebic liver abscess.  Ultrasonography, CT, or MRI can localize and delineate the size of the abscess cavity

 amebic colitis :detection of antigens in stool by ELISA  examination of stool samples  microscopy cannot differentiate between E. histolytica and E. dispar unless phagocytosed erythrocytes, which are specific for E. histolytica, are seen.

 Invasive amebiasis is treated with metronidazole (35–50 mg/kg/day in 3 divided doses for 7–10 days)or tinidazole (50 mg/kg/day once daily for 3 days) followed by treatment with a luminal amebicide : paromomycin(7 days), iodoquinol(20 days) OR Diloxanide furoate (7 days)  Asymptomatic intestinal infection with E. histolytica should be treated with paromomycin, which is preferred, or iodoquinol or diloxanide furoate.