Estimating the trend of the French BSE epidemic over six birth cohorts through the analysis of abattoir screening in 2001 and 2002

Abstract

- . Logistic regression models were run to compare the prevalence of BSE on successive birth cohorts, using a pair-wise method of controlling for age at testing; the prevalence on the first one, determined on animals slaughtered in 2001, was compared to the prevalence on the following one determined on animals slaughtered in 2002. Five models were performed in order to compare the birth cohorts preceding and following the months of June 1993 (i.e. July 92-June 93 birth cohort compared to July 93-June 94 birth cohort) (8.5 years old cattle), June 1994 (7.5 years old cattle), June 1995 (6.5 years old cattle), June 1996 (5.5 years old cattle) and June 1997 (4.5 years old cattle). The models were adjusted for the production type of cattle and the test used. The results showed a significant increase (OR = 2.31, 95% CI 1.08-4.9) of the BSE prevalence between the July 93-June 94 and July 94-June 95 cohorts, and then a significant decrease over the next two birth cohorts; the July 95-June 96 birth cohort was significantly less affected than the July 94-June 95 one (OR = 0.46, 95% CI 0.27-0.78), and the July 96-June 97 birth cohort was significantly less affected than the July 95-June 96 one (OR = 0.17, 95% CI 0.07-0.37). The increase in BSE prevalence between the July 93-June 94 and July 94-June 95 cohorts was in agreement with modelling studies, but needs to be confronted to the data on fallen stock at the national level. The decrease in BSE prevalence on the birth cohorts born after June 1995 was in agreement with the findings on the fallen stock in the western part of France and matches the implementation of the removal of specified risk materials (SRM) and dead animals from the processing of meat and bone meal (MBM) since June 1996. BSE / prevalence / epidemiology / abattoir screening / logistic regression

A spatio-temporal analysis of BSE cases born before and after the reinforced feed ban in France

“…As observed from the abattoir and fallen stock surveillance data, before the strong decrease of the risk that started on the birth cohort 1995-1996, the BSE prevalence was still increasing significantly in the overall French territory between the birth cohorts July 1993 through June 1994 and July 1994 through June 1995 [19]. However, the prevalence was similar for both birth cohorts in western France (3 regions including Brittany) [24].…”

“…However, the prevalence was similar for both birth cohorts in western France (3 regions including Brittany) [24]. It has been hypothesised [19] that exposure decreased earlier in western France than in any other part of France because feed manufacturers were more aware of the disease in this region. This is likely because the BSE index cases were in western France and the apparent incidence was higher than elsewhere.…”

“…They concluded BASB BSEcases were likely the result of an unsuccessful MBM ban and cross contamination of ruminant feed with feed containing MBM fed to poultry and pigs. More recently, a case study carried out in 2004 on 34 of these cases showed that maternal transmission can be ruled out for 82% (28) of the cases, and that 97% (33) of case farms used purchased proprietary concentrates but only 56% (19) purchased milk replacer [18].…”

Review on the epidemiology and dynamics of BSE epidemics

“…For example, in both the UK and France it has been identified that dairy cows have a risk of BSE approximately three times higher than that of beef cows, once confounding factors such as age at culling or region of origin have been accounted for [33,45,68]. This is simply explained by a higher use of compound feed in dairy farms.…”

“…This method was applied to French data [45] and provided evidence of a major decrease of the exposure between birth cohorts 94-95 and 95-96 for slaughtered animals (OR = 0.46, 95% CI 0.27-0.78). If the assumption of a steady surveillance is not fulfilled, the changes in the surveillance must be taken into account, which is possible using an APC model.…”