Entamoeba histolytica Infectious Agent Information Sheet Introduction Entamoeba histolytica is an anaerobic parasitic protozoan that infects the digestive tract of predominantly humans and other primates. The infection by E. histolytica is called Amebiasis. It usually occurs in the large intestine and causes internal inflammation, as suggested by its name (histo = tissue, lytic = destroying). Epidemiology and Clinical Significance Most infections by E. histolytica are asymptomatic, and clinical manifestations include amebic dysentery and extraintestinal disease. E. histolytica is estimated to infect about 50 million people worldwide with 40,000 to 100,000 deaths annually, making it the most common worldwide cause of mortality from a protozoan after malaria. The prevalence of Amebiasis is predominantly in tropical or subtropical environments in developing countries because of poor socioeconomic conditions and sanitation levels. In developed countries, Amebiasis is generally seen from migrants from and travelers to endemic areas. three weeks. Symptoms range from mild diarrhea to severe dysenteryproducing abdominal pain, diarrhea, and bloody stools. Treatment as determined by or on order of a physician is usually given with metronidazole, an antibiotic medication used particularly for anaerobic bacteria and protozoa, but does cause significant side effects. Prevention of amebic infection in travelers to endemic areas involves avoidance of untreated water in endemic areas and uncooked food, such as fruits and vegetables that may have been washed in local water. Diagnosis Traditionally, Entamoeba infections are diagnosed through microscopic examination of fresh or fixed fecal samples. However morphological diagnosis can be difficult because other parasites can look very similar to E. histolytica when seen under a microscope. The most common method is Direct Fecal Smear (DFS) and staining, but this does not allow identification to the species level. Recently, sensitive and specific serological and molecular techniques have been developed. These techniques include ELISA, immunoassay, and PCR. Pathogenesis, Immunity, Treatment and Prevention The parasite exists in two forms, a cyst stage (the infective form), and a trophozite stage (the form that causes invasive disease). Infection occurs following ingestion of amebic cysts; this is usually through contaminated food or water but can be associated with venereal transmission through fecal-oral contact. Cysts can remain viable for weeks to months, and ingestion of a single cyst is sufficient to cause disease. The cysts pass through the stomach to the small intestine where they excyst to form trophozoites. The trophozoites can penetrate the mucous barrier of the colon causing tissue destruction and increased intestinal secretion, and can thereby lead to bloody diarrhea. The parasites can also penetrate the intestinal wall and travel to organs such as the liver via the bloodstream causing extraintestinal amoebiasis. Clinical amebiasis generally has a subacute onset, usually over one to REFERENCES 1. Ngui R., et al. Differentiating Entamoeba histolytica, Entamoeba dispar and Entamoeba moshkovskii using nested PCR in rural communities in Malaysia. Parasites and Vectors. 2012 Sept; 5: 187. 3. Wilson I.W., Weedall G. D., Hall H. Host-parasite interactions in Entamoeba histolytica and Entamoeba dispar: what have we learned from their genomes. Parasite Immunology. 2012; 34: 90-99. 2. Tengku, S.A., Norhayati, M. Public health and clinical importance of amoebiasis in Malaysia: A review. Tropcial Biomedicine. 2011; 28(2): 194-222. 4. Bad Bug Book – Foodborne Pathogenic Microorganisms and Natural Toxins. 2nd Edition. Center for Food Safety and Applied Nutrition (FDA). 2012. © 2012 Luminex Corporation. All rights reserved. The trademarks mentioned herein are the property of Luminex or their respective owners. SS_452.01_0113