Fig 1.

(A) The infection cycle of G. lamblia (green) and E. histolytica (red). The protozoan cysts are ingested through contaminated food or water. Viable cysts undergo excystation after passing through the acidic environment of the stomach to release the trophozoites that attach or migrate to the intestines. Trophozoites will either remain in the lumen of the small intestines (G. lamblia) or invade through the colon mucosa (E. histolytica). The parasites also undergo encystation and excretion from the host body to further infect human populations through contaminated food and water supplies. (B) N. fowleri thrives in warm fresh water and hot springs. Under these conditions, N. fowleri infects humans via the nasal sinuses invading the brain and its infection causes swelling of the brain, termed primary amoebic meningoencephalitis (PAM).