Oocyst-Shedding Patterns of Three Eimeria Species in Chickens and Shedding Pattern Variation Depending on the Storage Period of Eimeria tenella Oocysts

Various species of Eimeria have different prepatent times and predilection sites, but their life cycles in infected poultry are similar. Practically speaking, chickens can be continuously exposed to various Eimeria species through environmental contamination. Furthermore, storage condition of the oocysts influences subsequent challenge infectivity, since coccidian oocysts contain a polysaccharide energy source known as amylopectin that is required for sporulation of oocysts and survival of the sporozoites. Here analysis of the oocyst-shedding patterns of 3 Eimeria species (Eimeria acervulina, Eimeria maxima, and Eimeria tenella) and the effects of different oocyst storage time (64, 143, 225, and 332 days) on subsequent propagation patterns were evaluated. Based on the analysis of oocyst-shedding patterns and infectious lesions evaluated by oocyst counts and histopathology, respectively, the peak points of oocyst production and infectious lesion generation in animals infected with E. acervulina were observed to occur earlier in comparison to E. maxima- and E. tenella-infected animals. Prolonged storage of E. tenella oocysts decreased oocyst excretion (measured as oocysts per gram of feces "OPG") and lengthened the peak period. Chickens infected with the freshest oocysts (Group A) had the highest fecal oocyst output, and animals in this group reached their peak at 7 days post-infection (dpi), which is similar to the normal pattern of oocyst output in fresh isolates. Infection with oocysts stored for longer periods showed a 1-day delay in the fecal oocyst peak count (8 dpi), and these infections also resulted in fewer OPG compared to Group A. Therefore, these results indicate that the storage period is important in affecting the peak point and pattern of oocyst shedding.