Characterization of bovine Sarcocystis species by analysis of their 18S ribosomal DNA sequences

Two Sarcocystis hirsuta isolates from 2 cattle (Bos taurus), 2 Sarcocystis hominis-like isolates from 2 cattle, 1 each Sarcocystis hominis-like isolate from a zoo-born dwarf zebu (B. taurus) and from a zoo-born bison (Bison bison), and 1 each Sarcocystis cruzi isolate from the dwarf zebu and the bison have been characterized by comparing the directly sequenced polymerase chain reaction products of their 18S rRNA genes. Sequences of 2 different isolates from the same species always showed a very high, nearly complete identity to each other both within all or only the conserved overlapping nucleotides. Thus, the 18S rDNA sequences of both S. hirsuta isolates proved to belong to a single species. The same is true for all 3 S. cruzi sequences. The 4 S. hominis-like isolates could not be placed within a single species using these criteria. They formed 2 separate groups (1 cattle isolate and the bison isolate, and the other cattle isolate and the dwarf zebu isolate). The results suggest that zoo-born large mammals do serve as intermediate hosts for Sarcocystis species known from indigenous herbivores, and that there might be another species found in cattle that is morphologically very similar to S. hominis.