Pathogenic Vibrio parahaemolyticus in Australian oysters
In 1999, Seafood Services Australia (SSA) initiated a risk-based approach to assessing and managing hazards. Regarding oysters, two risk assessments were undertaken, one on viruses and one on vibrios. Focusing on the latter hazards, the risks associated with the three main species: V. parahaemolyticus, V. vulnificus and V. cholerae were assessed. It was noted that V. parahaemolyticus (Vp) has recently caused major outbreaks in USA from consumption of oysters due to a “new” pathogenic type O3:K6. For Australia, no work on pathogenic Vp in oysters could be found, which introduced a great deal of uncertainty to the assessment. The RA noted that there had been two Vp poisonings in NSW from prawns imported from Indonesia, the clear inference being that pathogenic Vp exists in neighbouring waters.
In March, 2002 the FAO/WHO team will develop a global risk assessment of Vp in oysters. The RA will utilise the US risk model and insert data from the oyster industries of Canada, New Zealand, Australia and Japan. If no Australian data are available on levels of Vp the modellers will make assumptions which may well be disadvantageous to the Australian industry. This could happen if the north American mitigation strategy (rapid icing) to control of Vp is adopted as a prerequisite for export.
Failure to input Australian data into a Codex global risk assessment could have serious consequences for the industry. At best it would lead to protracted negotiation between Australia and Codex. These negotiations would need to be science-based and a research program would need to be funded. It is probable that the scale of this investigation would be at least a log scale larger than the present application.
Among the strategies to mitigate V. parahaemolyticus risk is chilling oysters as early as possible after harvest. In the case of the Canadian industry in British Columbia, the strategy has been used successfully in the summers of 2000 and 2001. This strategy is directly opposed to current summer handling practices by the NSW industry which allows product to remain as warm as 25°C for up to three days.
This project is designed to provide evidence of the occurrence and prevalence of pathogenic and non-pathogenic V. parahaemolyticus in Australian oysters. This knowledge will be invaluable to the NSW industry in particular - in case the FAO/WHO assessment recommends chilling of oysters as a pre-requisite for market access.
Effect of not doing the proposed study
If the work is not done and Codex Committee on Food Hygiene (CCFH) recommend a mitigation strategy of rapid icing, the local industry has a number of choices:
1. Ignore the CCFH recommendation on the grounds that we don’t export large volumes of oysters. The problem with this approach is that Codex has just as much application and force for domestic production as it does in the export arena.
2. Undertake a study to try to show that there is no problem with V. parahaemolyticus from Australian product. This would probably be a larger study than the present one and would be mounted to attempt to gain exemption for Australia. It’s always difficult to unwind global hygiene edicts.
The present project, for a relatively modest investment, effectively places Australian data into a global risk assessment. As such the data will have great force in the modelling phase. xbad
Final report
This project was designed to produce a “snapshot” of the prevalence of the bacterium Vibrio parahaemolyticus in Australian oysters during March and April of 2002.
V. parahaemolyticus occurs in two main forms: pathogenic and non-pathogenic. In the past 3 years there have been several large outbreaks of food poisoning in North America from oysters contaminated with the pathogenic type of V. parahaemolyticus.
This project examined samples of oysters from NSW, Tasmania and South Australia for the total and pathogenic V. parahaemolyticus. Single samples of 10-12 oysters were collected from selected sites in each state. Bacteria from these oysters were isolated and examined using DNA probes designed to detect either total or pathogenic V. parahaemolyticus isolates.
Keywords: Vibrio parahaemolyticus, oysters, pathogenicity, risk assessment.
