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University of Edinburgh - Parasitology terms Category: Education > Parasitology Date & country: 03/01/2018, UK Words: 18

Zygote
The stage arising from the fusion of a microgamete with a macrogamete. Gives rise to the oocyst stage

Zoite
A general term used for the invasive, extracellular form of tissue-cyst forming protozoa especially with Sarcocystis. Usually prefixed with another term e.g. bradyzoite.

Trophozoite
The free-living, feeding and reproductive stage of extracellular protozoa such as Balantidium and Trichomonas. Sometimes used to describe the migratory forms of Sarcocystis and Toxoplasma.

Unsporulated
Term used to describe an oocyst who's contents have not divided up into sporocysts and sporozoites and are not infective.

Sporulated
Term used to describe an oocyst who's contents have differentiated into sporocysts and sporozoites and is now infective.

Tachyzoite intermediate host.
The rapidly growing and dividing form of Toxoplasma that develops in during the early stage of infection that is responsible for disease. Found in both final and

Tachyzoite
The fast-growing, rapidly dividing form of Toxoplasma that develops in the early stages of infection and serves to distribute the parasite throughout the body of the host. Responsible for disease manifestation.

Sporozoite
The infective unit of the coccidia contained within the sporocysts of the sporulated oocyst. There are always 8 sporozoites per oocysts - i.e. 2 or 4 per sporocyst depending on the number of sporocysts.

Sporocyst
Component of the sporulated oocyst that contains the sporozoites. sporulated oocysts contain either 2 (Sarcocystis & Isospora) or 4 sporocysts (Eimeria).

Schizont
A multi-nucleate stage characteristic of the coccidia that forms inside infected cells early in infection. Sometimes referred to as meronts. Each nucleus eventually gives rise to a single merozoite. The process of schizont production (i.e. rapid nuclear division without cell formation) is called schizogony (or merogony).

Pseudocyst
Term sometimes used to describe the enlarged host cell when infected with Toxoplasma. Can refer to all cells infected i.e. tachyzoite and bradyzoites or just to the tachyzoite infected cells. The origin of the term comes from the lack of a distinct wall or membrane around the cell as in the cysts of Balantidium and sarcocysts of Sarcocystis.

Oocyst
The environmentally resistant form characteristic of the coccidia that develops from the zygote. Oocysts are passed out with the faeces either sporulated (Sarcocystis & Cryptosporidium) or unsporulated (Eimeria & Isospora). Produced by fusion of micro and macrogamete but overall similar in structure and function to the cysts of extracellular protozoa.

Meront
Alternative name for the schizont stage

Merozoite
Parasite stage developing from the schizont stage within the host cell as a result of asexual reproduction. They are long thin bodies often present in very large numbers. They eventually break out of the cell and establish the infection in other cells. Merozoites give rise to schizonts or gametocytes.

Gametocyte
The parasite stage in the coccidia that gives rise to the gamete stage. A macrogametocyte give rise to a single macrogamete while a microgametocyte gives rise to many microgametes.

Bradyzoite cyst
Term used to describe the cyst-like bodies containing bradyzoites found in the tissues of animals infected with Sarcocystis or Toxoplasma.

Cyst
Usually refers to the environmentally resistant, dormant form produced by extracellular protozoa such as Balantidium. Also used to describe enlarged host cells infected with Toxoplasma and Sarcocystis that become filled with parasite stages. See also pseudocysts and bradyzoite cysts.

Bradyzoite
The slow growing, metabolically reduced form of Toxoplasma and Sarcocystis that is found in the soft tissues of animals. They are the infective stage for the next host in the cycle. In Sarcocystis only found in the intermediate host but found in both final and intermediate hosts in Toxoplasma.