| Summary: | Thesis (Ph.D.)--University of Washington, 2020 Withering syndrome (WS) is a chronic bacterial disease of abalones, Haliotis spp., caused by a Rickettsia-like organism (WS-RLO). The etiological agent, Candidatus Xenohaliotis californiensis, occurs along the eastern Pacific margin of North America in California, US and Baja California, Mexico. However, as infected abalones have been transported to Chile, China, Taiwan, Iceland, Ireland, Israel, Spain, Thailand, and Japan, the geographic range of the bacterium is likely broad especially where California red abalone (Haliotis rufescens) are cultured or in areas where native species have been exposed to red abalone. Disease susceptibility varies among abalones with up to 99% losses of black abalone (H. cracherodii) in lab and field studies in the US, to no losses among the small abalone (H. diversicolor supertexta) in Thailand. Some abalone populations that have suffered severe WS mortality events have developed resistance to the disease. In addition, a newly identified phage hyperparasite of the WS-RLO may reduce pathogenicity and dampen associated losses. Proper diagnosis of WS requires the identification of infection with the pathogen (WS-RLO detected via in situ hybridization or histology coupled with PCR and sequence analysis) accompanied by morphological changes that characterize this disease (e.g. digestive gland metaplasia and pedal atrophy). A quantitative PCR (qPCR) assay was recently developed and validated for the detection of WS-RLO DNA in abalone tissues, feces, and seawater. While confirmation of infection cannot be done by PCR-based assays alone, they can be used as proxies for infection in areas where the WS-RLO is established and are recommended for inclusion in all abalone health examinations. Avoidance of WS is best accomplished by the establishment of a health history, good husbandry practices, and multiple health examinations prior to the movement of animals. Population declines in wild and cultured abalones due to WS have been well documented ...
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