• Single celled eukaryotes (nucleus): animalia, plantae, fungi, protista... including protozoa (either free-living or parasitic)

  • Protozoa is (1) motile (2) unicellular (3) eucaryote

Some protozoa have two-phase life cycles, alternating between proliferative phases (troph) and dormant cysts

  • Trophozoite (trophe, nourishment + zoon, animal): activated feeding stage in the life cycle of certain protozoa e.g Giardia (quickly die in the environment)

  • Cyst: infectious form (dormant stage that can survive in the environment)

Protozoan parasites that infect human:


Amoeboid motility (e.g. pseudopods), asexual reproduction (binary fission).


Flagellar (flagellum, whip) motility, asexual reproduction (binary fission)

  • Intestine: giardia (cysts/trophs), vagina/urethra: trichomonas vaginalis (trophs)

  • Kinetoplastida (flagellata characterised by the presence of an organelle with a large massed DNA called kinetoplast): Blood: trypanosoma brucei; Tissue (reticuloendothelial system, CNS): trypanosoma cruzi, (liver, spleen, skin/mucous membrane) Leishmania spp. 4 forms: Amastigote, Promastigote, Epimastigote, Trypomastigote (not leish)


Infectious stages: Sporozoite, Merozoite, Trophozoite, Hypnozoite, Gametocyte

Three major divisions of the living world

Protozoan parasites that infect human