Meningoencephalitis due to a sarcocystis neurona-like protozoan in Pacificharbor seals (Phoca vitulina richardsi)

Seven Pacific harbor seals with meningoencephalitis associated with Sarcocy stis neurona-like protozoa are described. Six of the 7 seals were free-rang ing and were found stranded over an 80-km stretch of central California coa stline; the other was captive. All had marked to severe nonsuppurative meni ngoencephalitis, most severe in the cerebellar cortex. Immunohistochemistry for S. neurona antigens was positive on brain tissue in all cases, reveali ng numerous merozoites as well as developing and mature schizonts. includin g rosette forms. Electron microscopy performed on 3 animals revealed merozo ites and schizonts consistent with Sarcocystis sp., with the absence of rho ptries in merozoites, lack of a parasitophorous vacuole around schizonts, a nd division by endopolygeny. Serology using western blotting revealed the p resence of anti-S. neurona immunoglobulins in the sera of 4 of 5 seals test ed. Four animals also had a concurrent mild to moderate nonsuppurative myoc arditis; in 1 seal, rare sarcocysts of undetermined species were present wi thin cardiomyocytes.