There have been some significant advances in our knowledge of QX disease of Sydney rock oysters in recent years. The pathogen has been isolated from many farming areas without being accompanied by patent disease and the influence of host fitness together with environmental effectors are now being implicated as disease precursors. Nonetheless, the devastating oyster mortalities in the Hawkesbury River this year (2005) highlight our problems in devising intelligent management strategies to minimise the impact of this disease.
A key obstacle to developing knowledge on parameters that control whether a disease outbreak will occur or whether the pathogen remains in estuaries at or beneath detectable levels is the lack of an experimental model of infection. In turn, the development of such a model is predicated on identifying the alternate (i.e. intermediate) host in the lifecycle of QX disease, a stage which is required for the pathogen to viably cycle repeatedly through an estuary. Furthermore, if an experimental model could be identified and later developed, obvious benefit would flow to strategic programs of selective breeding for disease resistant oysters. For example, an experimental model of infection would then provide a consistent and quantifiable challenge to assess the level of resistance in selected stock. Equally, the interactions of oyster immuno-competence and environment could then be assessed in a controlled system without the risk of spatial and temporal variation in QX disease prevalence and intensity that occur in natural estuarine systems.
A successful outcome of this research would have major benefit to our understanding of the biology of QX disease and have direct application to parallel projects aimed at benefitting the industry in both Queensland and New South Wales.