Coccidia Life Cycle

Coccidia - Joel Mills

Coccidia belong to the phylum Apicomplexa and are protozoan parasites of mammals, birds and reptiles. Coccidia have three major stages to their life cycle: Sporogony, Schizogony, Gametogony. The first two stages are asexual, with sexual reproduction occurring in the third stage. The following is a general life cycle though there is some variation in the various suborders.

Sporogony

Thick shelled oocysts are passed unsporulated in the feaces of the host, these consist of a single nucleus in a large pool of protoplasm. Sporulation occurs when conditions in the environment are suitable; high humidity, good oxygenation, and temerpatures around 27C. The nucleus will divide a number of times depending on the species of coccidia and the number of sporocysts it will form. After division of the nucleus the protoplasm will form conical bodies around each nucleus budding off from the central core. The nucleus and conical body together will then form a sproblast. The sporoblast will creates a wall for itself by secreting materials, at the same time the protoplasm forms two sporoziotes within the sporocyst wall. This process can take between 2 and 4 hours under optimal conditions but may take considerably longer if conditions are not suitable.

Schizogony

Sporozoites grow within intestinal epithelial cells

• • Sporozoites feed and grow

• As the sporozoite grows the nucleus divides forming a schizont

• The schizont contains numerous elongated merozoites

• The formation of merozoites is the first asexual reproductive stage called schizogony

• The schizont ruptures releasing the merozoites which also invade the epithelial cells

• Another generation of schizonts form which is the beginning of the sexual phase of reproduction called gametogony

• The merozoites form male microgamonts or female macrogamonts
  • Collectively known as gamonts or gametocytes

• The microgamonts released from the microgametocyte penetrate and fertilise the macrogamont (which is contained within the macrogametocyte)

• Gametogony forms the zygote
  • Surrounded by a cyst wall
  • Forms the oocyst

• The oocyst is passed in the faeces and is unsporulated

• The oocyst becomes sporulated in the second asexual reproductive phase called sporogony

• Once the oocyst is sporulated it is infective