Protozoal Infections

Detailed technical articles about protozoal infections below.

Protozoa are microscopic, one-celled organisms that can be free-living or parasitic in nature. They are able to multiply in humans, which contributes to their survival and also permits serious infections to develop from just a single organism. Transmission of protozoa that live in a human's intestine to another human typically occurs through a fecal-oral route (for example, contaminated food or water or person-to-person contact). Protozoa that live in the blood or tissue of humans are transmitted to other humans by an arthropod vector (for example, through the bite of a mosquito or sand fly).

The protozoa that are infectious to humans can be classified into four groups based on their mode of movement:

  • Sarcodina – the amoeba, e.g., Entamoeba
  • Mastigophora – the flagellates, e.g., Giardia, Leishmania
  • Ciliophora – the ciliates, e.g., Balantidium
  • Sporozoa – organisms whose adult stage is not motile e.g., Plasmodium, Cryptosporidium