ABSTRACT
Abalone aquaculture is a small but growing industry in Thailand and is based on both the exotic Haliotis diversicolor supertexta and the native H. asinina. Withering syndrome (WS) in abalone is caused by an infection with the Rickettsia-like organism (RLO) 'Candidatus Xenohaliotis californiensis' and has been spread to many countries globally. The present study reports the first observation of the WS-RLO agent in the small abalone, H. diversicolor supertexta in Thailand, Taiwan (ROC) and the People's Republic of China (PRC). Under light microscopy, the RLO was observed as intracytoplasmic inclusions within epithelial cells lining the post-esophagus and, to a minor extent, the intestine of H. diversicolor. Under transmission electron microscopy, inclusions were characterized as colonies of rod-shaped bacteria, 200 x 1800 nm in size, within a vesicle in the cytoplasm of the infected cell. The RLO from the small abalone bound with WS-RLO-specific in situ hybridization probes and was amplified by polymerase chain reaction (PCR), using primers designed from the 16S rDNA sequence of the original WS-RLO from California, USA. The PCR product of RLO samples from both the PRC and Thailand showed extremely high identity with the California WS-RLO (100 and 99%, respectively). These data combined with the history of abalone movements for aquaculture purposes indicate that RLOs observed in Thailand, Taiwan and the PRC are the WS-RLO that originated from California.
