Amebiasis Life Cycle
  • "Infection by Entamoeba histolytica occurs by ingestion of mature cysts 1 in fecally contaminated food, water, or hands.
  • Excystation 2 occurs in the small intestine and trophozoites 3 are released, which migrate to the large intestine. The trophozoites multiply by binary fission and produce cysts 4 , which are passed in the feces.
  • Because of the protection conferred by their walls, the cysts can survive days to weeks in the external environment and are responsible for transmission.
    • (Trophozoites can also be passed in diarrheal stools, but are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment.)
    • In many cases, the trophozoites remain confined to the intestinal lumen ( A: non-invasive infection) of individuals who are thus asymptomatic carriers and cysts passers. In some patients the trophozoites invade the intestinal mucosa ( B: intestinal disease), or, through the bloodstream, extraintestinal sites such as the liver, brain, and lungs ( C: extra-intestinal disease), with resultant pathologic manifestations. It has been established that the invasive and noninvasive forms represent separate species, respectively E. histolytica and E. disparindistinguishable.
  • Transmission can , which are morphologically also occur through fecal exposure during sexual contact (in which case not only cysts, but also trophozoites could prove infective)."
  • Courtesy of the Division of Parasitic Diseases at the National Center for Infectious Diseases, Centers for Disease Control and Prevension (public domain)