Submitted to: Parasitology International
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2010
Publication Date: 2/10/2011
Citation: Xiang, Z., He, Y., Rosenthal, B.M., Li, X., Zuo, Y., Feng, G., Cui, L., Yang, Z. 2011. Comparative studies confirm natural infections of buffaloes by Sarcocystis cruzi. Parasitology International. 127(2):460-466. Interpretive Summary: This paper resolves a diagnostic problem and sheds light on the natural epidemiology of bovine parasites that encyst in the muscle tissues of cattle and water buffalo. Whereas two distinct parasite species have been recognized in each host, this study has provided morphological and genetic data to instead substantiate the notion that the same parasite species is prevalent in each bovine host. This finding has specific relevancy to pathologist and food inspectors, and more generally bears on our notions of host specificity of this kind of parasite (broadening the range occupied by this, and arguably by other kinds of Sarcocystis including those that pose risks for human health).
Technical Abstract: Controversy exists concerning whether cattle and water buffalo sustain infections with cysts distinct arrays species in the genus Sarcocystis. In particular, morphologically similar parasites have been alternately ascribed to S. cruzi or to S. levinei, depending on their occurrence in cattle and water buffalo. We used light and transmission electron microscopy, genetic analysis, and experimental infections of definitive canine hosts to determine whether consistent differences could be identified from parasites derived from several natural infections of each host, examining several tissue types (esophagus, skeletal muscles, and heart). Cysts derived from cattle and water buffalo shared similar structure and similar 18SrRNA sequences, and induced similar outcomes in canine definitive hosts. One cattle specimen harbored unusually large (macroscopic) sarcocysts which nonetheless conformed to previously reported ultrastructural and genetic features of S. cruzi. Finding no basis to differentiate between them, we conclude that the parasites infecting each host and tissue type each correspond to S. cruzi, casting doubt on the validity of S. levinei, which evidently represents a junior synonym to S. cruzi. Evidently, this parasite cycles between dogs and a broader range of intermediate bovine hosts than was previously imagined.