Eimeria

Fig. 1. Life cycle of Eimeria spp. in chicken. For species and other hosts see Table 1. 1 After oral uptake of sporulated oocysts the sporozoites hatch in the small intestine from the sporocysts. 2–6 After penetration, multinucleate schizonts are formed (3) inside a parasitophorous vacuole (PV). The schizonts produce motile merozoites (DM, M), which may initiate another generation of schizonts in other intestinal cells (2–5) or become gamonts of different sex (7, 8). 7 Formation of multinucleate microgamonts, which develop many flagellated microgametes (7.1–7.2). 8 Formation of uninucleate macrogamonts, which grow to be macrogametes (8.1) that are characterized by the occurrence of two types of wall-forming bodies (WF₁, WF₂). 9 After fertilization the young zygote forms the oocyst wall by consecutive fusion of both types of wall-forming bodies (FW). 10 Unsporulated oocysts are set free via feces (exceptions are reptile- and fish-parasitizing Eimeria spp.). 11–13 Sporulation (outside the host) is temperature dependent and leads to formation of four sporocysts, each containing two sporozoites (SP), which are released when the oocyst is ingested by the next host. DG, developing microgametes; DM, developing merozoite; DW, developing wall-forming bodies; FW, fusion of WF₁ to form the outer layer of OW; M, merozoite; N, nucleus; NH, nucleus of host cell; OW, oocyst wall; PB, polar body (granule); PV, parasitophorous vacuole; R, refractile (= reserve) body; SB, sporoblast; SP, sporozoite; SPC, sporocyst; SPO, sporont; WF₁, wall-forming bodies I; WF₂, wall-forming bodies II; Z, cytoplasm of zygote (= young oocyst)