First Detection of Candidatus Xenohaliotis Californiensis, the Causative Agent of Withering Syndrome, in Japanese Black Abalone Haliotis discus discus in Japan

Abstract

Withering syndrome (WS) is a chronic wasting disease in abalone caused by ‘Candidatus Xenohaliotis californiensis’, a Rickettsia-like organism (RLO). Japanese black abalone Haliotis discus discus (14-34 mm in shell length) experienced monthly mortality rates of 3 to 10% from September 2010 to January 2011 with a cumulative mortality of 33% in a hatchery. Nine moribund animals were examined: five animals by histopathology and four by PCR. In histopathological examination, three animals exhibited basophilic, intracellular bacterial inclusions in the epithelium of the digestive tract. Severe infection was observed in the epithelium of the posterior portion of the esophagus of one animal. Morphological characteristics, and target tissues containing the inclusions were consistent with WS-RLO infection. In a PCR for 16S rRNA gene of WS-RLO, a specific fragment was amplified from all four animals, and nucleotide sequences of the amplicons were identical to that of the WS-RLO reported previously. The RLOs observed were conclusively identified as the agent of WS. Despite infection with the WS-RLO, our observations showed little degeneration of the digestive gland and shrinkage of the foot muscle both of which are critical pathological changes in WS. This is the first report of the WS-RLO found in Japanese black abalone in Japan.