Question
What are the possible mechanisms for cow to calf transmission of BSE; and what assessment he has made of the most likely route.
Answer
Mr. Alan W. Williams: To ask the Minister of Agriculture, Fisheries and Food what are the possible mechanisms for cow to calf transmission of BSE; and what assessment he has made of the most likely route. [12776] Mrs. Browning: Whether or not maternal transmission occurs is still open to question. The final results of the cohort study, for which preliminary results were published in August 1996, will shortly be presented to the Spongiform Encephalopathy Advisory Committee. It is clear however that if maternal transmission does occur it does so only infrequently. To try to establish which tissues might be involved in maternal transmission, blood, constituent parts of placenta, embryos, uterine washings and milk were inoculated into mice. In separate experiments, milk was also fed to mice. None proved to be infectious. In another experiment, calves were fed the homogenised placentae of infected cows as this was considered, by extrapolation from known evidence for sheep scrapie, to be the most likely route of transmission. The exposed calves survived without developing clinical BSE for seven years, and have recently been killed so that their tissues can be examined for the presence of infectivity. Finally, another large experiment is assessing the role of the embryo itself in transmitting disease. Embryos collected from infected, and clinically affected, cows were implanted into surrogate dams imported from New Zealand, and the surviving calves and their surrogate dames remain under observation in order to determine whether they succumb to BSE. That experiment will not end however until 2001, when the youngest calf reaches seven years of age. Under the circumstances, the most likely routes of transmission from cow to calf have already been examined. Should it prove necessary however, following interpretation of the cohort study, some or all of these options will be revisited as advised by SEAC.