Molecular characterization of Sarcocystis neurona genotypes in California sea lions (Zalophus californianus) with polyphasic rhabdomyositis.

A unique clinical syndrome characterized by polyphasic rhabdomyositis associated with Sarcocystis neurona has been reported in both free-ranging and managed care California sea lions (CSLs; Zalophus californianus). The pathogenesis of this disease is poorly understood. Specific S. neurona genotypes have been associated with more severe sarcocystosis and mortality in other marine mammals; however, S. neurona genotypes infecting CSLs with rhabdomyositis have not yet been investigated. The objective of this study was to characterize genotypes of S. neurona from CSLs with rhabdomyositis and to compare these with genotypes described in other marine and terrestrial hosts. Archived skeletal muscle samples from 25 affected free-ranging CSLs were screened for S. neurona DNA using polymerase chain reaction (PCR) targeting a multi-copy locus (ITS1), followed by genotype characterization using a PCR-based multilocus sequence typing approach targeting six polymorphic loci. Among these 25 CSLs, 15 different S. neurona genotypes were identified. Of these, six have been previously identified in southern sea otters (Enhydra lutris nereis) and/or other hosts, but the remaining nine have not been reported in any host to date. This study, although limited in sample size, demonstrates a wide diversity of S. neurona genotypes infecting free-ranging CSLs affected with rhabdomyositis, some shared with other hosts in the region, but many others that appear to be unique to sea lions.