Meningoencephalitis Due to a Sarcocystis Neurona-like Protozoan in Pacific Harbor Seals (Phoca vitulina richardsi)

Abstract

Seven Pacific harbor seals with meningoencephalitis associated with Sarcocystis neurona-like protozoa are described. Six of the 7 seals were free-ranging and were found stranded over an 80-km stretch of central California coastline; the other was captive. All had marked to severe nonsuppurative meningoencephalitis, most severe in the cerebellar cortex. Immunohistochemistry for S. neurona antigens was positive on brain tissue in all cases, revealing numerous merozoites as well as developing and mature schizonts, including rosette forms. Electron microscopy performed on 3 animals revealed merozoites and schizonts consistent with Sarcocystis sp., with the absence of rhoptries in merozoites, lack of a parasitophorous vacuole around schizonts, and division by endopolygeny. Serology using western blotting revealed the presence of anti-S. neurona immunoglobulins in the sera of 4 of 5 seals tested. Four animals also had a concurrent mild to moderate nonsuppurative myocarditis; in 1 seal, rare sarcocysts of undetermined species were present within cardiomyocytes.

Sarcocystis Meningoencephalitis in a Northern Gannet (Morus bassanus)

“…Because we did not evaluate muscle cysts using PCR we could not verify that cysts were the same species of Sarcocysts as those in the brain. Brain lesions were most severe in the cerebellum, similar to that reported in Pacific harbor seals (Phoca vitulina richardsi) (Lapointe et al, 1998). This case is also similar to other cases in seals (Lapointe et al, 1998) and turkeys (Teglas et al, 1998;Dubey et al, 2000), because sarcocysts were also observed in both striated muscle and myocardium.…”

“…Brain lesions were most severe in the cerebellum, similar to that reported in Pacific harbor seals (Phoca vitulina richardsi) (Lapointe et al, 1998). This case is also similar to other cases in seals (Lapointe et al, 1998) and turkeys (Teglas et al, 1998;Dubey et al, 2000), because sarcocysts were also observed in both striated muscle and myocardium. Sarcocystis falcatula was ruled out in one of the turkeys without protozoal encephalitis because schizonts were not found in endothelial cells and the organism did not react to anti-S. falcatula antibody.…”

“…They plunge dive to forage on shoaling pelagic fish. Reports of Sarcocystis encephalitis in sea otters (Ehydra lutris nereis) and harbor seals on the west coast of North America (Lapointe et al, 1998;Rosonke et al, 1999;Lindsay et al, 2000) indicate the intermediate host is not necessarily restricted to non-marine habitats. Harbor seals and sea otters both spend time on land and so could acquire infections there.…”

Improvement of Western Blot Test Specificity for Detecting Equine Serum Antibodies toSarcocystis Neurona

“…12,14 The culture-confirmed S. neurona true-positive serum samples used in this analysis were highly consistent in their reactivity to those specific proteins. The results of this study also demonstrate that the Western blot S. neurona antibody test can be subject to false-positive results because of antibody cross-reactivity.…”

“…7 Recent work indicates that immunodominant proteins of approximately 29 and 17 kD are specific to S. neurona, which suggests a different criterion for a positive test than that reported previously. 12,14 The purposes of this study were to develop the most stringent criteria possible for a positive test result, to estimate the sensitivity and specificity of the EPM Western blot antibody assay, and to test the ability of bovine antibodies to S. cruzi to act as a blocking agent to prevent false-positive results in the Western blot test for S. neurona.…”