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Animal Experiments: BSE

Volume 468: debated on Thursday 29 November 2007

To ask the Secretary of State for Environment, Food and Rural Affairs what Veterinary Laboratories Agency experiments have been conducted on cows fed with BSE infected material in the last 20 years; and what the results were. (167619)

[holding answer 27 November 2007]: No studies have ever been conducted by VLA in which cattle were fed with BSE infected material.

Seven individual experiments have been conducted at VLA that involved the oral dosing of cattle with bovine brain tissue known to be infected with the BSE agent. The material, in the form of a suspension, was administered directly on to the back of the tongue with a syringe. These studies represent three clusters of experiments, with individual experiments within each cluster being related in terms of the objectives of the investigations conducted.

Two experiments investigated the susceptibility of calves to oral challenge to different doses of brain tissue, ranging from 300g to 1mg. A correlation was recognised between dose and the incubation period, but infection was achieved at all dose levels. Below a dose of 100g however, not all exposed calves became infected, and the efficiency of transmission declined with reducing dose. Although incomplete, data from these studies were published recently1.

Three other experiments investigated the pathogenesis of BSE in cattle, although the latest, and largest, was primarily intended to provide tissues and fluids at varying time points in the incubation period to enable the evaluation of diagnostic tests. These studies involved the sequential slaughter of cattle, and collection of tissues, during the incubation period, from shortly after exposure to the point of clinical disease. There have been several publications that have described the scientific outcomes of the first pathogenesis study, but the most recent2 summarises all previous results. Additional data from a smaller study, and an opportunistic evaluation of data from the largest pathogenesis study, have also been published recently3, 4, 5.

The last two experiments were established to enable the collection of fluids, such as blood samples, during the course of the incubation period to enable their investigation as potential targets for diagnosis of BSE before onset of clinical disease. These transpired to be negative studies, not only in terms of tests investigated at VLA but also when materials were shared with other researchers. As a result, there have been no scientific publications related to these studies.

Reference List

1 Arnold, M. E; Ryan, J. B M; Konold, T.; Simmons, M. M; Spencer, Y. I; Wear, A.; Chaplin, M.; Stack, M.; Czub, S.; Mueller, R.; Webb, P.R; Davis, A.; Spiropoulos, J.; Holdaway, J.; Hawkins, S. A C; Austin, A. R, and Wells, G. A H. Estimating the Temporal Relationship Between PrPSc Detection and Incubation Period in Experimental Bovine Spongiform Encephalopathy of Cattle. (2007). Journal of General Virology. 88: 3198-3208.

2 Wells, G. A. H.; Spiropoulos, J.; Hawkins, S. A. C., and Ryder, S. J. Pathogenesis of experimental bovine spongiform encephalopathy: Preclinical infectivity in tonsil and observations on the distribution of lingual tonsil in slaughtered cattle. (2005) Veterinary Record; 156 :401-407.

3 Terry, L. A. ; Marsh, S. ; Ryder, S. J.; Hawkins, S. A. C.; Wells, G. A. H., and Spencer, Y. I.. Detection of disease-specific PrP in the distal ileum of cattle exposed orally to the agent of bovine spongiform encephalopathy. (2003); Veterinary Record. 152; 387-392.

4 Wells, G. A H; Konold, T.; Arnold, M. E; Austin, A. R; Hawkins, S. A C; Stack, M.; Simmons, M. M; Lee, Y. H; Gavier-Widen, D.; Dawson, M., and Wilesmith, J. W. Bovine Spongiform Encephalopathy: the Effect of Oral Exposure Dose on Attack Rate and Incubation Period in Cattle. (2007) Journal of General Virology. 88: 1363-1373.

5 Masujin, K.; Matthews, D.; Wells, G. A. H.; Mohri, S., and Yokoyama, T. Prions in the Peripheral Nerves of Bovine Spongiform Encephalopathy-Affected Cattle. (2007) Journal of General Virology; 88:1850-1858.