Completion of the life cycle of Sarcocystis neurona

Sarcocystis neurona is the most important cause of a neurologic disease in horses, equine protozoal myeloencephalitis (EPM). The complete life cycle o f S. neurona, including the description of sarcocysts and intermediate host s, has not been completed until now. Opossums (Didelphis spp.) are definiti ve hosts, and horses and other mammals are aberrant hosts. In the present s tudy, laboratory-raised domestic cats (Felis domesticus) were fed sporocyst s from the intestine of a naturally infected opossum (Didelphis virginiana) . Microscopic sarcocysts, with a maximum size of 700 x 50 mum, developed in the muscles of the cats. The DNA of bradyzoites released from sarcocysts w as confirmed as S. neurona. Laboratory-raised opossums (D. virginiana) fed cat muscles containing the sarcocysts shed sporocysts in their feces. The s porocysts were similar to 10-12 x 6.5-8.0 mum in size. Gamma interferon kno ckout mice fed sporocysts from experimentally infected opossums developed c linical sarcocystosis, and S. neurona was identified in their tissues using S. neurona-specific polyclonal rabbit serum. Two seronegative ponies fed s porocysts from an experimentally-infected opossum developed S. neurona-spec ific antibodies within 14 days.