<i>Sarcocystis rommeli</i>, n. sp. (Apicomplexa: Sarcocystidae) from cattle (<i>Bos taurus</i>) and its differentiation from <i>Sarcocystis hominis</i>

Abstract

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