Background Infections with Sarcocystis spp. in sheep (Ovis aries) are globally prevalent and pose significant health and economic concerns. Nine Sarcocystis taxa, comprising seven identified species and two unclassified entities, are known to form sarcocysts in sheep. Macroscopic sarcocysts with elongated villar protrusions are rare, having been reported only twice: as S. mihoensis in Japan and as an S. mihoensis -like organism in Spain. This study reports the first identification of this morphological type in China. Methods Muscle samples were collected from 83 domestic sheep in Kunming City, China, between March and September 2025. Sarcocysts were characterized morphologically using light microscopy (LM) and transmission electron microscopy (TEM). For molecular analysis, genomic DNA was extracted from individual sarcocysts isolated from different sheep. Five genetic markers—the nuclear 18S rDNA, 28S rDNA, and ITS-1 regions, the mitochondrial cox1 gene, and the apicoplast rpoB gene—were amplified, sequenced, and analyzed. Results A novel sarcocyst type was detected via LM in 6 out of 83 (7.2%) domestic sheep. These macroscopic sarcocysts measured up to 6230 μm in length and 341 μm in width, and possessed a thick cyst wall with numerous sloping villar protrusions (VPs) measuring 6.9–11.9 μm in length. Ultrastructurally, the VPs were 5.8–9.3 μm long and 0.8–1.1 μm wide, lined by an electron-dense layer, and contained scattered microtubules that extended from the apex to the base. Sequence comparisons with GenBank entries revealed the highest sequence similarities with S. buffalonis for 18S rDNA (97.6–98.0%), S. miescheriana for 28S rDNA (92.1–92.3%), S. japonica for cox1 (81.2–81.8% identity), and S. arctica for rpoB (88.5–88.8% identity). No significant matches were found for the ITS-1 region. Genetic divergence analysis against other sheep-infecting species indicated the smallest distances with S. medusiformis at 18S rDNA (0.0582), S. gigantea at 28S rDNA (0.0556), and S. gigantea at cox1 (0.2922). Given the distinct morphological features and the unique molecular characteristics, this organism is proposed as a new species, Sarcocystis chenggongensis n. sp. Conclusions The discovery of this new species marks the third global report of macroscopic sarcocysts with elongated villar protrusions, confirming a broad geographical distribution for this rare morphotype. Persistent taxonomic uncertainties, due to inconsistent data, require future research to resolve the group’s evolution and life cycles. Graphical Abstract

Morphological and molecular characterization of Sarcocystis chenggongensis n. sp. (Apicomplexa: Sarcocystidae) in domestic sheep (Ovis aries) from China

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2026年3月9日

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Junjie Hu,
Luyao Qian,
Danqu Lamu,
Shuangsheng Deng,
Yuning Zhang,
Yurong Yang

摘要

Background

Infections with Sarcocystis spp. in sheep (Ovis aries) are globally prevalent and pose significant health and economic concerns. Nine Sarcocystis taxa, comprising seven identified species and two unclassified entities, are known to form sarcocysts in sheep. Macroscopic sarcocysts with elongated villar protrusions are rare, having been reported only twice: as S. mihoensis in Japan and as an S. mihoensis -like organism in Spain. This study reports the first identification of this morphological type in China.

Methods

Muscle samples were collected from 83 domestic sheep in Kunming City, China, between March and September 2025. Sarcocysts were characterized morphologically using light microscopy (LM) and transmission electron microscopy (TEM). For molecular analysis, genomic DNA was extracted from individual sarcocysts isolated from different sheep. Five genetic markers—the nuclear 18S rDNA, 28S rDNA, and ITS-1 regions, the mitochondrial cox1 gene, and the apicoplast rpoB gene—were amplified, sequenced, and analyzed.

Results

A novel sarcocyst type was detected via LM in 6 out of 83 (7.2%) domestic sheep. These macroscopic sarcocysts measured up to 6230 μm in length and 341 μm in width, and possessed a thick cyst wall with numerous sloping villar protrusions (VPs) measuring 6.9–11.9 μm in length. Ultrastructurally, the VPs were 5.8–9.3 μm long and 0.8–1.1 μm wide, lined by an electron-dense layer, and contained scattered microtubules that extended from the apex to the base. Sequence comparisons with GenBank entries revealed the highest sequence similarities with S. buffalonis for 18S rDNA (97.6–98.0%), S. miescheriana for 28S rDNA (92.1–92.3%), S. japonica for cox1 (81.2–81.8% identity), and S. arctica for rpoB (88.5–88.8% identity). No significant matches were found for the ITS-1 region. Genetic divergence analysis against other sheep-infecting species indicated the smallest distances with S. medusiformis at 18S rDNA (0.0582), S. gigantea at 28S rDNA (0.0556), and S. gigantea at cox1 (0.2922). Given the distinct morphological features and the unique molecular characteristics, this organism is proposed as a new species, Sarcocystis chenggongensis n. sp.

Conclusions

The discovery of this new species marks the third global report of macroscopic sarcocysts with elongated villar protrusions, confirming a broad geographical distribution for this rare morphotype. Persistent taxonomic uncertainties, due to inconsistent data, require future research to resolve the group’s evolution and life cycles.

Graphical Abstract