Targeted surveillance to assess the prevalence of BSE in high‐risk populations in western France and the associated risk factors

Abstract

A pilot study was set up for the first time in France in August 2000, to obtain more precise estimates on the BSE epidemic in France. Three categories of cattle at risk of BSE (found dead on-farm, euthanased and emergency slaughtered) were sampled exhaustively from August 7 to December 22, 2000, in the three regions assumed to be the most affected with BSE in France (Basse-Normandie, Bretagne and Pays de la Loire). The samples were checked by using Prionics tests, and positive samples were confirmed by Western blot or immunohistochemistry. The overall prevalence of positive cattle was 0.16 per cent. Multifactorial logistic regression showed that there was a significantly higher prevalence among cattle from the birth cohorts July 1993 to June 1994 and July 1994 to June 1995, than among those born before July 1993, and among the categories 'euthanased' and 'emergency slaughtered' than among the category 'dead on-farm, and a higher prevalence in the regions Pays de la Loire and Bretagne than in Basse-Normandie. No significant differences in the prevalence of BSE were observed between dairy, beef suckler and mixed herds.

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

“…These variables can hence hardly be confounders for the analysis of the trend of the epidemic. This is the reason why we did not include the geographical origin of the animal in the models, even if it is known to be a risk factor [11,20,23]. It helped to keep the study as powerful as possible.…”

“…It has been shown that the percentage of BSE cases found either through the Mandatory Reporting System or through the different active surveillance programmes (on fallen stock and at the abattoir) varies with time and space [12,20]. It might be possible that some animals with mild clinical signs were sent to the abattoir, instead of being declared to the mandatory reporting system, since it has been found that about 7% of the animals tested positive at the abattoir had shown some clinical signs suggestive of BSE [7].…”

“…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).…”

“…A comprehensive analysis of the data concerning fallen stock was performed [21] over a three year period in western France where a pilot study started in June 2000 [20]. It showed that, on animals dead or subjected to euthanasia, the prevalence of positive BSE tests decreased for animals born after June 1995.…”

Review on the epidemiology and dynamics of BSE epidemics

“…Although the largest numbers of tested cattle were healthy slaughtered cattle, the majority of positive cases occurred in the suspected cases and risk populations [29,47,48]. On average throughout the EU, the likelihood of finding BSE cases is more than 20 times higher in the risk populations than in healthy slaughtered cattle.…”