Sarcocystis rommeli, n. sp. (Apicomplexa: Sarcocystidae) from Cattle (Bos taurus) and its Differentiation from Sarcocystis hominis.

Abstract

Cattle (Bos taurus) are intermediate hosts for three named species of Sarcocystis, S. cruzi, S. hirsuta, and S. hominis. Recently, a fourth species was identified and named S. sinensis. However, S. sinensis originally named a species of Sarcocystis in water buffalo (Bubalus bubalis) in China. Based on unverifiable evidence, it was suggested that the same parasite infects cattle. In addition, S. sinensis was recently declared as nomen nudum because its naming violated the rules of International Code of Zoological Nomenclature. Thus, the fourth species using cattle as an intermediate host does not have a valid name. Here, we propose a new name, Sarcocystis rommeli for the S. sinensis-like parasite from cattle in Argentina, and differentiate it ultrastructurally from S. hominis sarcocysts from experimentally infected cattle. Sarcocystis rommeli sarcocysts were microscopic with a 5-μm-thick wall with slender villar protrusions (Vp); the Vp were up to 5μm long, up to 0.5μm wide, and of uneven thickness, often bent at an angle. The ground substance layer (Gs) was up to 0.8μm thick and smooth. Vesicular structures were seen at the base of the Vp. The bradyzoites were 10-12μm long. Sarcocystis hominis sarcocysts had Vp that were often upright, up to 7.5μm long, and up to 1.8μm wide; the Gs was up to 2μm thick and without vesicles. Its sarcocyst wall was up to 5.6μm thick, the vp were bent at an angle, up to 5.8μm long, the Gs was up to 2μm thick, but without vesicles seen in S. rommeli. Beef containing sarcocysts of S. rommeli was not orally infectious for two human volunteers and a red fox (Vulpes vulpes). The Sarcocystis described here is molecularly different from S. cruzi, S. hirsuta, and S. hominis based on 18S rRNA and cox1 gene sequences.