Fig. 1

Major developmental stages of Eimeria. Eimeria life-stages within the host occur once except in merozoite where there can be two or more generations. Only sporulated oocysts are infective and may remain inactive until excystation is activated by enzymatic reaction in the host gut to liberate two to four sporocysts from which sporozoites are released. The sporozoites then transform into merozoites, trophozoites, gametocytes and then oocysts, which are released with host egesta. The distinction between early and late oocysts cannot only be explained away by sporulation as oocysts may remain unsporulted for a long time in the environment. MG: merozoite generation