What is it?
Intracytoplasmic infections with Xenohaliotis californiensis, a rickettsial bacterium, in gastrointestinal epithelia causes
disease (termed withering syndrome) in wild and farmed abalones, Haliotis spp. Withering syndrome occurs at elevated water temperatures (~18˚C and above) in abalones with
moderate to severe infections.
Where and when might it occur?
Xenohaliotis californiensis occurs along the south-west coast of North America in California, US and Baja California, Mexico.
However, as infected abalones have been transported to Chile, China (Peoples Rep. of), Chinese Taipei, Iceland, Ireland, Israel, Japan, Spain and Thailand and possibly other countries, the geographical range of the aetiological agent is suspected to be broad where California red abalones, Haliotis rufescens, are cultured or areas where native species have been exposed to red abalones.
Abalones with X. californiensis infections may be subclinically infected during the prepatent period or at water temperatures of 15˚C.
Signs of the disease include pedal atrophy, mottled digestive gland, anorexia, weakness and lethargy.
The disease is characterised by intracytoplasmic bacterial inclusions within the posterior oesophagus, intestine and absorptive/transport epithelia of the digestive gland, whereas moderate to advanced infections are typically associated with degenerative or metaplastic changes within the digestive gland, followed by pedal muscle atrophy in susceptible species.
Infected individuals may be slightly to severely emaciated (atrophied) under permissive water temperatures.
Control and treatment
The most effective prevention is avoidance of the pathogen. Should infection occur, holding abalones at < 15˚C may reduce RLO transmission and subsequent disease transmission. Application of oxytetracycline reduces losses.