Protozoa are the simplest, most primitive type of animal, consisting of a single cell. They are resistant to antibiotics.
Some protozoa have life stages alternating between active stages (e.g., trophozoites) and dormant cysts.
- Cysts:As cysts, protozoa can survive harsh conditions, such as exposure to extreme temperatures or harmful chemicals, or long periods without access to nutrients, water, or oxygen for a period of time. Being a cyst enables parasitic species to survive outside of a host, and allows their transmission from one host to another.
- The conversion of a trophozoite to cyst form is known as encystation, while the process of transforming back into a trophozoite is known as excystation.
- Amastigote: Does not have visible external flagella or cilia. The term is used mainly to describe a certain phase in the life-cycle of trypanosome protozoans. It is also called the leishmanial stage, since in Leishmania it is the form the parasite takes in the vertebrate host, but occurs in all trypanosome genera.
- Promastigote: This is a stage in the insect host. Promastigotes enter the blood when a person is bitten by the insect. They quickly enter the amastigote stage (see above). Ideally we would have referred to include the amastigote stage rather than the promastigote stage for some vials, but we have included the promastigote stage if the amastigote stage was not available at this time.
- Trophozoite: (Greek: trophē, nourishment + zōon, animal) is the activated, intracellular feeding stage in the life cycle.
Reproduction: Protozoa can reproduce by binary fission or multiple fission. Some protozoa reproduce sexually, some asexually, while some use a combination, (e.g., Coccidia). An individual protozoan is hermaphroditic.