are unicellular organisms
that live in moist environments (including soil). Most protozoans
are free-living, meaning they do not require a host
to survive. A small percentage of protozoans
cause human disease. Most protozoans
in adverse conditions.
- Amoebas are large protozoans that move by pseudopods.
- Example: Entamoeba histolytica causes amoebic disentery (intestinal disease)
- Flagellates move using one or more flagella.
- Examples: Trichomonas vaginalis (sexually transmitted disease) and Giardia lamblia (causes diarrhea)
- Ciliates move by using cilia.
- Example: Balantidium coli (intestinal disease)
- These very small protozoans can enter the host cell. They also often need two hosts to complete their life cycle.
- Example: The Plasmodium sporozoan causes malaria. Its primary host is mosquitoes, who inject the immature protozoans into humans to complete its life cycle.