Description of extended pre-harvest pig Salmonella surveillance-and-control programme and its estimated effect on food safety related to pork.

Salmonella in pork can be combated during pre- or post-harvest. For large slaughterhouses, post-harvest measures like decontamination might be cost-effective while this is less likely with small-to-medium sized slaughterhouses. In this study, pre-harvest measures might be more relevant. We describe an extended surveillance-and-control programme for Salmonella in finisher pigs, which, to establish equivalence to the Swedish control programme, is intended for implementation on the Danish island, Bornholm. The effect of the programme on food safety was estimated by analysing Salmonella data from pig carcasses originating from herds that would have qualified for the programme during 2006-2008. Food safety was interpreted as prevalence of Salmonella on carcasses as well as the estimated number of human cases of salmonellosis related to pork produced within the programme. Data from the Danish Salmonella programme were obtained from Bornholm. We used a simulation model developed to estimate the number of human cases based on the prevalence of Salmonella on carcass swabs. Herds are only accepted in the programme if they have one or less seropositive sample within the previous 6 months. In this way, the Salmonella load is kept to a minimum. The programme is not yet in operation and pigs that qualify for the programme are currently mixed at slaughter with those that do not qualify. Therefore, we had to assess the impact on the carcass prevalence indirectly. The prevalence of Salmonella in carcass swabs among qualifying herds was 0.46% for the 3 years as a whole, with 2006 as the year with highest prevalence. According to the simulation the expected number of human cases relating to pork produced within the programme was below 10. When the programme is in operation, an extra effect of separating pigs within the programme from those outside is expected to lower the prevalence of Salmonella even further.

Identification of inbred strains of mice: II. Characterization of different substrains of the C3H strain.

Substrains of inbred C3H mice differ significantly in their genetic constitution with respect to biochemical markers, skin grafting, and skeletal variations. The presence of such discrepancies among substrains poses a problem when comparing conclusions based on experiments done in different substrains. Therefore, methods of controlling the genetic constitution are necessary and important to avoid these discrepancies.

C-type virus protein p30 in blood from inbred mice correlates with their later incidence of leukemia.

The major core protein, p30, of mouse C-type viruses was quantitated radioimmunologically in lymphoid organs and blood from inbred strains of mice. The concentration of p30 in thymus and spleen had a weak and moderate correlation, respectively, to leukemia frequency. In contrast, the concentration of p30 in blood from mice with a high incidence of leukemia (strains AKR and C58) was 100-fold increased at 2 months of age compared with 10 strains with a low incidence of the disease. The SJL mice, which have a high incidence of reticulum cell neoplasms, showed generally elevated, but variable, values. The high concentration in AKR blood developed during the first weeks of life. Approximately one-third of the DBA/2 mice had elevated levels after 4 to 5 months, whereas the values from mice of the 129 strain were low irrespective in their age. The major part of p30 appeared to be associated with the erythrocytes. The concentration of p30 in the blood seems to reflect the presence of replicating virus in mice. It identifies among the inbred strains a high leukemia group one-half year prior to disease.

Effect of separate transport, lairage, and slaughter on occurrence of Salmonella typhimurium on slaughter carcasses.

The study aimed to reduce cross-contamination between finishers from Salmonella-positive and Salmonella-negative herds during transport, lairage, and slaughter, thereby reducing the prevalence of Salmonella Typhimurium on slaughter carcasses. In Phase 1 of the study, pigs from Salmonella-negative herds were kept in lairage for 2-4 hours either in clean pens (intervention group) or pens contaminated with Salmonella-infected faeces (control group). All pigs were slaughtered on the same slaughterline, and carcass swabs 24 hours after slaughter revealed a low degree of cross-contamination in the pens: there was no difference in Salmonella-positive carcasses between intervention (1.7%) and control groups (0.8%). In Phase 2, control pigs from Salmonella-negative herds were mixed with pigs from Salmonella-positive herds during lairage for 2-4 hours, while the intervention group still consisted of pigs from Salmonella-negative herds. All pigs were slaughtered on the same line: first intervention, then control. Carcass swabs taken 24 hours after slaughter failed to show a reduction in Salmonella-positive carcasses in the intervention group (4.5%) compared with the originally Salmonella-negative pigs in the control group (3.6%). In pigs from Salmonella-positive herds the occurrence of Salmonella was substantially higher at 10.4%. When the results were corrected for 6 carcass samples found positive with S. Heidelberg on the same day, which was attributed to a transient hygiene failure, only 2.2% of the carcasses in the intervention group were Salmonella-positive. We conclude that even though cross-contamination occurs in the abattoir pens, its importance on the slaughter line may be greater. However, the final results of this study should be awaited to conclude whether separate slaughter of pigs from Salmonella-positive and Salmonella-negative herds should be recommended.