Case Report: Sarcocystosis in a Sheep
A 6-year-old sheep was slaughtered at a Brazilian abattoir after stunning with a captive bolt pistol. During inspection, the esophagus, pharynx, tongue, and diaphragm were condemned due to numerous white nodules infiltrating the mucosa and muscle layers. Six additional carcasses displayed similar lesions and were also condemned. No abnormalities were noted during antemortem inspection. Affected tissues were submitted to the Veterinary Pathology Section at the Federal University of Rio Grande do Sul for histopathology and molecular testing.
Clinical and Gross Findings
The esophagus contained more than ten ellipsoid, white, soft, plaque-like nodules (0.5 × 0.2 × 0.1 cm to 1.1 × 0.5 × 0.3 cm) distributed across the serosal surface and extending into the muscle layer. Similar lesions were observed in the pharynx, tongue, and diaphragm. On sectioning, nodules were cystic, filled with translucent gelatinous fluid.
Histopathology
H&E-stained sections revealed multiple 300–800 µm cystic structures within the muscular layer, surrounded by a delicate capsule and fibrous connective tissue. Cysts contained central septa and numerous crescent-shaped, ~4 µm bradyzoites morphologically consistent with Sarcocystis gigantea. Adjacent tissue showed mild lymphocytic inflammation. Identical cysts were also observed in the diaphragm and tongue.
Molecular Findings
PCR amplification of the 18S rRNA gene followed by Sanger sequencing confirmed 99.5% identity with Sarcocystis gigantea (GenBank accession MT026577.1).
Morphologic Diagnosis
Protozoal cysts, multifocal, esophagus, tongue, diaphragm.
Case Summary
The findings support a diagnosis of sarcocystosis caused by Sarcocystis gigantea. This parasite produces macrosarcocysts in the skeletal muscles of sheep, most commonly the esophagus, pharynx, tongue, and diaphragm. Though macrosarcocyst-forming species are generally of low pathogenicity and not zoonotic, affected carcasses are often condemned due to the visible lesions and concerns over meat quality, resulting in economic losses for producers.
Comments
Sarcocystis spp. are widespread protozoan parasites requiring two hosts: carnivores (definitive hosts) and herbivores (intermediate hosts). In sheep, six species are recognized, with dog-transmitted species typically more pathogenic than cat-transmitted species such as S. gigantea. Prevalence varies with husbandry practices and host exposure.
While S. gigantea infections are usually subclinical, macrosarcocysts can reach several millimeters to 1 cm in size, distorting muscle fibers and prompting carcass condemnation at slaughter. Despite the lack of zoonotic risk, heavy infections cause significant economic losses to the sheep industry. Molecular methods remain a valuable diagnostic tool when gross or microscopic findings are inconclusive.
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