In vitro excystation of Caryospora simplex (Apicomplexa:Eimeriorina)

In vitro excystation of sporozoites of the heteroxenous coccidian Caryospora simplex Leger, 1904 (Apicomplexa: Eimeriorina) is described. Sporocysts freed mechanically from oocyts released a maximum of 51% of their sporozoites within 45 min at 25 degree C and a maximum of 74% within 20 min at 37 degree C when incubated in a 0.25% (w/v) trypsin-0.75% (w/v) sodium taurocholate (bile salt) excystation solution. At emergence from sporocysts, sporozoites were weakly motile then became highly active after about 2 min in excystation solution. Sporozoites within sporocysts exposed to bile salt only became highly motile within 25 min at 25 degree C and within 15 min at 37 degree C but did not excyst. When exposed only to trypsin at the above temperatures, the Stieda body dissolved; the substieda body remained intact, and the sporozoites exhibited only limited motility within sporocyts; only a few excysted. Intact, sporulated oocysts incubated at 25 degree or 37 degree C in 0.02 M cystein-HCl and a 50% CO sub(2) atmosphere for 18 h had no morphologic changes in the oocyst wall. Further incubation of these intact oocysts in excystation solution for 30 min at 37 degree C caused neither motility of sporozoites within sporocysts nor excystation. Grinding oocysts for 30 sec in a motor-driven, teflon-coated tissue grinder caused motility of some sporozoites within sporocysts but did not result in excystation.