Fig. 1. Weakness is noted as a narrow-based stance of the horse: thoracic and pelvic limbs closer together and a lower carriage of head and neck. Notably, there is muscle atrophy, especially of the epaxial muscles (top line more visible).
lecular testing identified S. fayeri as the parasite present in the skeletal muscle. A subset of horses (n 10/35) with sarcocystosis
from this study were treated orally with 15% pona- zurilb (5 mg/kg, every 25 h) for 15–28 days. Clinical
signs of weakness, stiffness, apparent pain on pal- pation, and gait deficits subsided within 15 days of treatment, and muscle mass returned to normal within 1–2 months (not published data). After the publication of this study, 12 additional horses with
Fig. 2. Hematoxylin and eosin at 10, formalin-fixed. Note 2 sarcocysts within myofibers (top right of figure) and inflammatory infiltrates consisting mainly of T-lymphocytes (CD8 and CD4 [left of figure], immunostaining not shown here). Calibration bar 100 m.
