How the surveillance system may bias the results 
of analytical epidemiological studies on BSE: 
prevalence among dairy versus beef suckler cattle 
breeds in France

Ducrot, Christian; Roy, Pascal; Morignat, Eric; Baron, Thierry; Calavas, Didier

doi:10.1051/vetres:2002065

Cited by 27 publications

(30 citation statements)

References 15 publications

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“…So, in order to define a study sample in which cases and controls have been submitted to a global comparable level of risk, they were matched on their birth cohort. The production type of cattle, dairy or beef, was also considered as a potential confounding factor [13,23]. Since the farmer practices concerning the cattle feeding were related 512 N. Jarrige et al to the production type, it was decided not to pair cases and controls on this factor to avoid a possible overmatching bias but to consider it as a potential confounder in the model.…”

Section: Discussionmentioning

confidence: 99%

Case-control study on feed risk factors for BSE cases born after the feed ban in France

Jarrige¹,

Ducrot²,

Cazeau³

et al. 2007

Vet. Res.

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-In France, after the ban on meat and bone meal (MBM) in cattle feeding in June 1990, cases of Bovine Spongiform Encephalopathy (BSE) have continued to be detected in bovines born after that ban (called BAB cases). A case-control study was therefore carried out to determine the way these cases were contaminated. A multivariate conditional model was built adjusting for the production type of the animals and taking into account the herd size. The results confirmed that feeding cattle with proprietary concentrates was at risk for BSE, with an adjusted odds ratio of 6.8 (2.5; 18.7) for the consumption of less or three different proprietary concentrates and 17.6 (5.7; 54.8) for more than three, when comparing with no consumption of proprietary concentrates, considering feeding of bovines before the age of two. The results suggest that cross-contaminations by MBM in bovine concentrates have occurred after 1990. To a lesser extent, on-farm cross-contaminations, i.e. consumption by cattle of feedstuffs initially dedicated to other animals and which could legally contain MBM, have probably also existed, since the presence on farms of poultry fed purchased feed involved an increased risk of BSE with an odds ratio of 1.8 (1.1; 3.0). The use of milk replacers, which often incorporates animal fats, was also at risk with an odds ratio of 1.8 (1.0; 3.1).BSE / cross-contamination / cattle feeding / proprietary concentrates / France

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Section: Discussionmentioning

confidence: 99%

Case-control study on feed risk factors for BSE cases born after the feed ban in France

Jarrige¹,

Ducrot²,

Cazeau³

et al. 2007

Vet. Res.

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“…Since then different complementary surveillance programmes have been organised [1], based on rapid tests [22]; they showed that the clinical surveillance alone misses a great proportion of diseased animals [15,20]. This is the reason why a comprehensive system is now implemented to detect BSE cases, including clinical surveillance, test on dead cattle (fallen stock), and systematic screening at the abattoir; the tests are carried out on cattle aged two years and more (over 30 months old before July 2001 at the abattoir).…”

Section: Introductionmentioning

confidence: 99%

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

Bonnardière

Calavas²,

Abrial³

et al. 2004

Vet. Res.

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- . 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

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“…It could be demonstrated through retrospective investigations that more than half of the cases found by active surveillance had displayed clinical signs before death, either characteristic for BSE or at least sufficiently suggestive [18,29]. Also, comparing cases found by active and passive surveillance during the same period of time (passive surveillance takes place before death/slaughter) showed biases in the type of animals detected by passive surveillance, the ability to detect beef cow cases being far less efficient than detection of dairy cases [33].…”

Section: Active Surveillancementioning

confidence: 99%

“…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.…”

Section: Risk Factorsmentioning

confidence: 99%

“…These statistical models, logistic regression and APC models enable other variables that are linked to the prevalence to be taken into account, such as the production a. Countries with the highest incidences type [33] or the season of birth 12 , and then remove these confounders in the estimate of the trend of prevalence. The major drawback of APC model is that the three factors are linearly linked.…”

Section: Evolution Of the Bse Prevalence Over Yearsmentioning

confidence: 99%

See 1 more Smart Citation

Review on the epidemiology and dynamics of BSE epidemics

Ducrot¹,

et al. 2008

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-The paper describes how the comprehensive surveillance of bovine spongiform encephalopathy (BSE) and studies carried out on these data has enhanced our knowledge of the epidemiology of BSE. Around 7 000 BSE cases were detected through the screening of about 50 million cattle with rapid tests in Europe. It confirmed that the clinical surveillance had a poor capacity to detect cases, and also showed the discrepancy of this passive surveillance efficiency between regions and production types (dairy/beef). Other risk factors for BSE were being in a dairy herd (three times more than beef), having a young age at first calving (for dairy cattle), being autumn-born (dairy and beef), and being in a herd with a very high milk yield. These findings focus the risk on the feeding regimen of calves/heifers. Several epidemiological studies across countries suggest that the feedborne source related to meat and bone meal (MBM) is the only substantiated route of infection -even after the feed ban -, while it is not possible to exclude maternal transmission or milk replacers as a source of some infections. In most European countries, the average age of the cases is increasing over time and the prevalence decreasing, which reflects the effectiveness of control measures. Consistent results on the trend of the epidemic were obtained using back-calculation modelling, the R 0 approach and Age-Period-Cohort models. Furthermore, active surveillance also resulted in the finding of atypical cases. These are distinct from previously found BSE and classified in two different forms based on biochemical characteristics; their prevalence is very low (36 cases up to 1st September 2007), affected animals were old and some of them displayed clinical signs. The origin and possibility of natural transmission is unknown.

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How the surveillance system may bias the results of analytical epidemiological studies on BSE: prevalence among dairy versus beef suckler cattle breeds in France

Cited by 27 publications

References 15 publications

Case-control study on feed risk factors for BSE cases born after the feed ban in France

Case-control study on feed risk factors for BSE cases born after the feed ban in France

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

Review on the epidemiology and dynamics of BSE epidemics

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