Examination of artificial oocyst excystation methods in the murine coccidium, <i>Eimeria krijgsmanni</i>

Eimeria spp. cause coccidiosis characterized by diarrhea and induce serious economic losses in livestock industries. Although several anti-coccidial drugs are currently available, the emergence of resistant strains and drug residues is problematic; therefore, the development of new drugs is needed. Since sporozoites of Eimeria spp. invade host intestinal epithelial cells and numerous merozoites are formed, drugs that target sporozoites are expected to be useful. We previously used murine Eimeria krijgsmanni as a model to examine anti-coccidial drug susceptibility; however, few studies have conducted drug evaluations against sporozoites. The establishment of excystation protocols is essential for progress in in vitro experiments using sporozoites because oocysts must be isolated from feces using complex techniques before the excystation process. Various artificial excystation protocols have been reported for each Eimeria spp.; however, those for E. krijgsmanni have not yet been examined. Therefore, 4 protocols described in previous studies were herein conducted for E. krijgsmanni. Pepsin was important for excystation in rodent Eimeria spp., and this was also the case for E. krijgsmanni. Excystation rates were higher with the physical disruption of oocyst walls than with pepsin. An incubation in HBSS containing 0.25% (w/v) trypsin and 0.1% (w/v) sodium taurocholate after a physical treatment achieved higher and the most stable excystation rates. Modifications to this method were also examined, and no improvements were observed. The optimal excystation protocol for E. krijgsmanni was elucidated as of now.