Haplosporidium nelsoni and H. costale in the Pacific oyster Crassostrea gigas from China's coasts.

We examined 220 Pacific oysters Crassostrea gigas obtained from 11 locations along China's coasts for the presence of the 2 protistan parasites Haplosporidium nelsoni (MSX; multinucleated sphere X) and H. costale (SSO; seaside organism). Haplosporidium-like plasmodia were histologically observed in 9 oysters (4.09%) from 7 locations. Five oysters had mixed infections, and 4 oysters were infected only with H. nelsoni as determined by in situ hybridization (ISH) and polymerase chain reaction (PCR). This is the first report of H. nelsoni and H. costale infection in bivalves in Chinese waters.