Bovine Spongiform Encephalopathy and Spatial Analysis of the Feed Industry

Abstract

In France, despite the ban of meat-and-bone meal (MBM) in cattle feed, bovine spongiform encephalopathy (BSE) was detected in hundreds of cattle born after the ban. To study the role of MBM, animal fat, and dicalcium phosphate on the risk for BSE after the feed ban, we conducted a spatial analysis of the feed industry. We used data from 629 BSE cases as well as data on use of each byproduct and market area of the feed factories. We mapped risk for BSE in 951 areas supplied by the same factories and connection with use of byproducts. A disease map of BSE with covariates was built with the hierarchical Bayesian modeling methods, based on Poisson distribution with spatial smoothing. Only use of MBM was spatially linked to risk for BSE, which highlights cross-contamination as the most probable source of infection after the feed ban. In France, meat-and-bone meal (MBM) has been banned from cattle feed since July 30, 1990. However, through January 1, 2007, 957 cases of bovine spongiform encephalopathy (BSE) have been detected in cattle born after the ban. These cases provide evidence that BSE control has not been entirely effective, which poses a concern because BSE is a zoonotic disease, a source of variant CreutzfeldtJakob disease (vCJD). Until now, 158 defi nite or probable cases of vCJD in humans have been detected in the United Kingdom (www.cjd.ed.ac.uk/fi gures.htm, consulted March 12, 2007) and 21 in France (www.invs.sante.fr/recherche, consulted March 12, 2007). The risk for humans is controlled by removing specifi ed risk materials from human consumption (since 1996 in France, later in other European countries) and testing all cattle at the abattoir with a rapid test (since 2001 in continental European Union). However, these measures are expensive. Achieving 100% control of the spread of BSE is a major challenge, important for human health but limited by economic constraints.The main hypothesis concerning the source of infection in cattle born after the MBM ban still involves MBM; the BSE agent may have entered cattle feed by cross-contamination with feed for monogastric species (pigs and poultry) in which MBM was still authorized until November 2000. Cross-contamination could have occurred within factories, during feed delivery to the farm, or on mixed farms that have cattle and pigs or poultry. This hypothesis is supported by the fi nding of MBM traces in cattle feed (1) as well as by epidemiologic studies that showed a spatial link between density of monogastric species and risk for BSE (2-7).Another hypothesis, however, suggests the role of other animal byproducts such as fat and dicalcium phosphate (DCP) derived from bones, which were not prohibited in cattle feed before 2000. Such components might have been contaminated by the BSE agent during cattle slaughter (1). Clauss et al. (5) found a statistically higher use of milk replacers (which contain animal fat) for calves on BSE-affected farms in Germany, and the same type of association was observed in France for scrapie in sheep (8).More knowledge about...

Review on the epidemiology and dynamics of BSE epidemics

“…The potential for cross-contamination is heightened by the potential for low-dose exposure causing infection; in an oral exposure study it was shown that cattle could become infected by as little as 1 mg of brain homogenate [63]. A statistically significant relationship between the pig density in a region and BAB cases has also been found in subsequent studies on both the GB data [58] and for other countries including Northern Ireland, France, Switzerland, and Spain [1,3,26,30,55], supporting this initial hypothesis of cross-contamination of cattle feed with feed intended for pigs, and possibly poultry; a spatial study on feed factories confirmed recently the use of MBM in monogastric feed as a risk factor for BSE [51]. Further evidence on the BAB cases arising from the feedborne source has been provided by Sheridan et al [57], where a spatial relationship between feed-producers and BSE cases was found.…”

Spatial risk mapping for rare disease with hidden Markov fields and variational EM

“…The Bovine Spongiform Encephalopathy (BSE) is a noncontagious neurodegenerative disease in cattle. This sudden and unexpected disease threatened bovine production in Europe and has been intensively studied, in particular, for spatial patterns [Abrial et al (2005a), Allepuz et al (2007), Paul et al (2007)]. It is transmitted by meat and bone meal.…”

“…Geography and topography are not, however, important explanatory factors for the disease which should rather be related to local agricultural traditions. In these regions there is a high density of monogastric species [Abrial et al (2005a)], for example, pigs and poultry, and meat and bone meal were used to feed these species [Paul et al (2007)]. It is suspected that the BSE risk can be explained by cross-contamination with an ingredient used in poultry or pig feed.…”

BSE risk and the use of meat and bone meal in the feed industry: perspectives in the context of relaxing control measures

“…A statistically significant relationship between pig density and the number of BAB cases has been shown in France as well as in other countries, including Northern Ireland, Switzerland and Spain (Allepuz et al, 2007;Denny & Hueston, 1997;Doherr et al, 2002;Schwermer & Heim, 2007), supporting the hypothesis of cross-contamination of cattle feed with feed intended for pigs and possibly poultry. To analyze in greater detail at which stages of the feed chain cross-contaminations may have played a role in the spread of BSE in France, a spatial study of feed factories was carried out that confirmed the use of MBM in monogastric feed as a risk factor for BSE (Paul et al, 2007). In parallel, a case-control study at the farm level demonstrated that the use of compound feed for young cattle, and the presence of poultry operations on farms, using compound feed, were risk factors for BSE, thus providing further evidence of the role of compound feed in the risk of BSE.…”

“…The underlying hypothesis was that the different local contexts of feed processing factories contributed to varying capacities to manage crosscontaminations. Quantitative data collected from March 2004 to June 2005 by the Ministry of Agriculture (Direction générale de l'alimentation) in 1014 feed factories in France (Paul et al, 2007) were used to describe the local contexts of feed production in France. In addition, qualitative data were collected in Bretagne in June 2006.…”