Schizonts of Sarcocystis speeri Dubey and Lindsay, 1999 were cultured in vi
tro in bovine monocyte and equine kidney cell cultures inoculated with infe
cted tissues of nude and gamma-interferon knockout mice fed sporocysts from
opossums, Didelphis albiventris. At least 1 asexual cycle was completed in
3 days. In vitro-grown merozoites were structurally and antigenically dist
inct from those of Sarcocystis neurona and Sarcocystis falcatula. Culture-d
erived merozoites of S. speeri were not infective to budgerigars (Melopsitt
acus undulatus).