B. Austin, D. A. Austin, Z. Farhat, P. A. W. Robertson
Vibrio harveyi has emerged as a major pathogen of finfish and shellfish, particularly in South America and South East Asia. Previously, diagnosis has relied on a conventional phenotypic approach, comparing the results of biochemical tests with diagnostic tables. However, using monospecific polyclonal antibodies, an enzyme linked immunosorbent assay and western blotting system were developed, and demonstrated to be capable of detecting and differentiating 10^3 cells of V. harveyi in diseased animals and water. Control of infections has been possible with antimicrobial compounds, e.g. oxolinic acid, but less success has resulted with probiotics or vaccines. In particular, vaccine development, using inactivated whole cells and purified subcellular components, has led to products which are extremely toxic to whole animals and cell cultures. Indeed, mortalities after challenge often exceeded those of the positive controls, i.e. unvaccinated but challenged animals. The problems reflect the lack of efficacy of bacterial inactivation systems, namely formalin, glutaraldehyde, chloroform, alcohol or acetone. Thus after chemical treatment, toxic compounds remain in the vaccines. Conversely, heat inactivation has led to safe but ineffective vaccines.
(Department of Biological Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14, 4AS Scotland, UK)