Cooperative Fish and Wildlife Research Units Program: Washington
Education, Research and Technical Assistance for Managing Our Natural Resources

Withering Syndrome, WS, is a fatal disease of abalone caused by a Rickettsia-like organism (WS-RLO). The causative agent, “Candidatus Xenohaliotis californiensis”, occurs along the eastern Pacific margin of North America in California, USA and Baja California, Mexico. However, as infected abalones have been transported to Chile, China (People’s Rep. of), Taiwan, Iceland, Ireland, Israel, Spain, Thailand, and most recently Japan, and possibly other countries, the geographical range of the etiological agent is suspected to be broad where California red abalones, Haliotis rufescens, are cultured or in areas where native species have been exposed to this species. Susceptibility varies among species with up to 99% losses of black abalone, H. cracherodii, in lab and field studies in the USA to no losses among H. diversicolor supertexta in Thailand. Some populations that have suffered catastrophic losses to WS have developed an increased resistance to the disease. In addition, a newly identified phage hyperparasite of the WS-RLO may reduce pathogenicity and dampen losses from the WS-RLO. Diagnosis of WS requires the identification of infection with the pathogen (WS-RLO via in situ hybridization or via histology coupled with PCR and sequence analysis) accompanied by morphological changes that characterize this disease (e.g. pedal and digestive gland atrophy, and digestive gland metaplasia). A real-time PCR (qPCR) assay has been developed and may be useful in quantifying amounts of pathogen DNA. Confirmation of infection by the WS-RLO cannot be done by PCR analysis alone as this method only detects pathogen DNA, but can be used as a proxy for infection in areas where the agent is established. Control measures include avoidance, culling infected animals and, as per federal regulations, oral or bath treatment with oxytetracycline. Avoidance is best accomplished by the establishment of a health history and multiple health examinations prior to movement of animals. Although histology or in situ hybridization are required to confirm infection, qPCR is able to detect small amounts of pathogen DNA and is advised to be included as part of health examinations.