How is Entamoeba histolytica commonly transmitted to humans?

• A. Inhalation of contaminated air
• B. Direct skin contact with contaminated surfaces
• C. Ingestion of cysts in contaminated water or food
• D. Mosquito bite

Answer: (C)

The main concept here is that Entamoeba histolytica spreads through a fecal-oral route via hardy cysts. The infectious form is the cyst, which is shed in human feces and can survive in the environment. People become infected when they ingest these cysts in water or food that has been contaminated by feces, especially in areas with poor sanitation or untreated drinking water. Once inside the small intestine, the cysts excyst to trophozoites that invade the intestinal lining and can cause dysentery; they may even spread to the liver and form abscesses in more severe cases. Inhalation, direct skin contact with contaminated surfaces, or bites from vectors like mosquitoes are not how this parasite is transmitted, which is why ingestion of contaminated water or food is the correct route.