Microbial risk assessment within Q-PorkChains
By Francis Butler
Within the Q-PorkChains project there is a small but active group working on microbial risk assessment of pork and pork projects. The project team consists of Biosystems Engineering, University College Dublin and Teagasc, Ashtown Food Research Institute, Dublin. The group carried out three separate risk assessments for Salmonella in the pork chain – a farm level risk assessment, an assessment of the slaughter / processing of pork and finally the group considered the risk from consumption of typical UK/ Irish fresh pork sausages.
This product was considered, according to Professor Butler, the leader of the risk assessment group, as it is a comminuted product so consequently the pathogen is potentially distributed right through the sausage and there is also a risk of undercooking by the consumer with the accompanying risk of illness from ingesting Salmonella.
While three separate risk assessments were developed within the Q-PorkChains project, this article focuses on the outcomes of the farm level risk assessment. The approach adopted in this risk assessment was a novel dynamic model using existing data from published literature that describes the dynamics of Salmonella Typhimurium in modern intensive pig farms. The study is the first approach so far to build a dynamic model for Salmonella Typhimurium at the compartment level of the pig farm based on sets of differential equations in order to predict the prevalence of different risk groups of pigs at the slaughterhouse, given the different load of the pathogen in the compartment. The basic concept of the model is shown in Figure 1.
Figure 1: Conceptual representation of the farm Salmonella model
Pigs are initially free of Salmonella (susceptible) but if exposed to the pathogen can become infected, either as high shedding pigs (high infectious) or low shedding (low infectious) depending on the environmental conditions. After being infectious for a period of time, the pigs stop shedding the organism but become carriers. Thereafter they become immune with antibody protection and finally they can become susceptible again when the immunity wears off.
By modelling this disease cycle, the model can predict the percentage of animals in each of the different categories at different stages in the pig production cycle. An example of the outputs of the model is shown in Figure 2 where the variation in the percentages of animals in the different categories with time is shown. Commenting on the outcomes from the risk assessment models, Professor Butler from University College Dublin concluded that it was important that good risk assessment models be made available through the Q-PorkChains project to risk managers so that they can objectively quantify the risk and, as important, properly assess the effectiveness of intervention strategies at key points in the pork food chain.
Figure 2: Typical output from the farm model showing the propagation of Salmonella Typhiminurum in a ‘compartment’ in a pig farm in a ‘highly’ contaminated environment
| Salmonella is a pathogen of significant public health concern. A total of 190,000 cases of human salmonellosis were reported by 25 Member States in 2004 and the overall incidence in the EU was approxi-mately 40 per 100,000 population. Pork, after eggs and poultry meat, is a major source of human foodborne salmonellosis in the European Union (EU). Consequently there is ongoing concern by the pork industry, regulatory authorities and other stakeholders to control Salmonella throughout the full pork food chain. EFSA is currently considering the risk of Salmonella in pork and it is opportune that the Q-PorkChains project has developed quantitative risk assessments of Salmonella in pork at separate stages in the food chain to allow a informed debate take place on the level of the risk and the role of intervention strategies at various stages in the chain to control the pathogen. |
