Submitted to: Journal of Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/20/1999
Publication Date: N/A
Citation: Interpretive Summary: Parasites of the genus Sarcocystis are single-celled organisms that can cause anemia, weigh loss, abortion and death in livestock. Although Sarcocystis infection is common in horses, the parasite has not been shown to infect the liver. Scientists at the Beltsville Agricultural Research Center and the University of California, Davis report for the first time severe acute hepatitis in a horse from California. The results will be of use to parasitologists, pathologists, and veterinarians.
Technical Abstract: Hepatic sarcocystosis was diagnosed in a horse in association with refractory bacterial osteomyelitis and plasma-cell tumor of the maxilla and hepatic salmonellosis. Gross lesions included pleural, pericardial, and peritoneal effusions, serosal hemorrhages, hepatomegaly, gastric ulceration, colonic edema, and proliferative tissues filling 2 maxillarydental alveoli. Histologically, liver was characterized by severe suppurative, necrotizing, periportal hepatitis, and severe periacinar necrosis. Hepatocytes frequently contained protozoal schizonts in various stages of development. In mature schizonts, merozoites were often arranged radially around a central residual body, consistent with asexual division by endopolygeny. Ultrastructural features of merozoites included an apical conoid and polar ring, anterior micronemes, central nuclei, and absence of rhoptries. These protozoa did not react to antisera raised against Neospora caninum, Sarcocystis neurona, Toxoplasma gondii, or Hammondia hammondi. The microscopic and ultrastructural characteristics and immunoreactivity of this organism are consistent with a Sarcocystis sp. other than S. neurona. This is the first report of Sarcocystis-associated hepatitis in a horse. The life cycle of this organism and source of infection are unknown.