IN-VITRO CULTIVATION OF THE VASCULAR PHASE OF SARCOCYSTIS-SINGAPORENSIS

To establish an in vitro culture system for the precystic phase of Sar cocystis singaporensis, we initially tested various excysting fluids f or sporocysts. An excysting fluid containing 2.5% bovine taurocholate and 10% bile of the specific intermediate host, Rattus norvegicus, in RPMI medium was the most suitable resulting in excystation of 80% of t he sporozoites. Subsequently, we identified brain endothelial cells an d pneumonocytes of the rat to promote growth of sporozoites to schizon ts. Hepatoma, fibroblastic, or myoblastic cells were not suitable for the parasite's development. First-generation schizonts were seen at da ys 3-10 postinoculation (PI); a distinct second peak of schizogonic de velopment only occurred in endothelial cells at days 14-18 PI. First-g eneration schizonts were 26.0 (+/- 3.8) mu m in diameter and contained 32-50 merozoites, second-generation schizonts measured 34.4 (+/- 10.6 ) mu m and contained 54-72 merozoites. Merozoite yield at large-scale culture conditions (75 cm(2) flasks) using pneumonocytes as host cells was relatively low. Ultrastructurally, sporozoites and merozoites wer e quite similar to corresponding stages of other Sarcocystis species. With regard to host cell specificity and developmental kinetics, in vi tro cultivation showed close similarities to the situation in vivo.