Morphology of Sarcocystis gigantea in experimentally-infected sheep

Abstract

The development of the parasite and lesions was studied in 32 sheep killed 10 days to 47 months after inoculation with Sarcocystis gigantea sporocysts from cats. At 21–42 days post-inoculation (d.p.i.), there was a mild encephalitis, but organisms were not seen in the brain. Immature sarcocysts were detected from 40–84 d.p.i. The cyst wall was not measurable by light microscopy at 40 d.p.i., but was 1.5 –2 μm thick at 84 d.p.i. At 119 d.p.i. both immature cysts containing only metrocytes, and mature cysts containing both metrocytes and merozoites, were present. These mature cysts did not have a secondary cyst wall. A mature cyst, 350 μm in length, was found in a sheep killed at 8 1 2 months p.i. At 10 m.p.i. cysts were up to 0.5 mm long and a secondary cyst wall was present. At 47 m.p.i. cysts were 2–5 × 4.5–7.5 mm, and were found only in the muscles of tongue, oesophagus, pharynx and flank.