DESCRIPTION OF A NEW NEOSPORA SPECIES (PROTOZOA, APICOMPLEXA, SARCOCYSTIDAE)

Neospora hughesi n. sp. was isolated from the central nervous system t issue of an adult equine (Equus caballus) from California. The tachyzo ites are crescent-shaped, approximately 2 X 5 mu m (1.8-3.0 X 4.0-7.0 mu m), with characteristic apical complex structures consisting of an anterior polar ring, conoid, numerous rhoptries filled with a uniform electron-dense material, and 22 microtubules extending posteriorly fro m the polar ring. Comparison of N. hughesi to canine and bovine Neospo ra caninum isolates showed phenotypic differences in immunoreactive pr oteins. Molecular analysis of the small subunit ribosomal RNA gene rev ealed no differences in the nucleotide sequence between N. hughesi and N. caninum isolates examined. However, the internal transcribed space r I region revealed 7 nucleotide base differences between N. hughesi a nd N. caninum isolates (CN1 and BPA1) analyzed in this study. The exis tence of nucleotide base differences in the internal transcribed space r regions suggests that this region may be a genetic marker for discri minating species within the genus Neospora. The ultrastructural, antig enic, and molecular data support distinction of N. hughesi as a new sp ecies, separate from N. caninum, the only recognized species in this g enus.