Simpson C F, Mayhew I G
J Protozool. 1980 Aug;27(3):288-92. doi: 10.1111/j.1550-7408.1980.tb04259.x.
Equine protozoal myeloencephalitis (EPM) was diagnosed in 10 horses. By electron microscopy, schizonts were found in intact host cells of the spinal cords or, more frequently, free in the extracellular spaces. Developmental stages of schizonts differed morphologically, and the late stage of schizogony was characterized by endopolygeny. These findings permitted tentative identification of the protozoon as a Sarcocystis sp. Free merozoites were present in the extracellular spaces or in cells of the spinal cord. Pericytes of capillaries were most frequently parasitized by merozoites were present in the extracellular spaces or in cells of te spinal cord. Pericytes of capillaries were most frequently parasitized by merozoites, but the cytoplasm of neurons, macrophages, intravascular and tissue neutrophils, and axons of myelinated nerve fibers also contained these organisms. The presence of parasites in the cytoplasm of tissue and circulating neutrophils suggest that this putative Sarcocystis sp. may have a hematogenous phase of infection.
10匹马被诊断出患有马属动物原虫性脑脊髓炎（EPM）。通过电子显微镜观察，裂殖体存在于脊髓完整的宿主细胞中，或者更常见的是游离于细胞外间隙。裂殖体的发育阶段在形态上有所不同，裂体生殖的后期以内生多殖为特征。这些发现初步确定该原生动物为一种肉孢子虫属（Sarcocystis sp.）。游离的裂殖子存在于细胞外间隙或脊髓细胞中。毛细血管周细胞最常被裂殖子寄生，裂殖子存在于细胞外间隙或脊髓细胞中。毛细血管周细胞最常被裂殖子寄生，但神经元、巨噬细胞、血管内和组织中的中性粒细胞的细胞质以及有髓神经纤维的轴突中也含有这些生物体。组织和循环中性粒细胞的细胞质中存在寄生虫表明，这种假定的肉孢子虫属可能有血源性感染阶段。
