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BSE maternal transmission route remains a mystery

Whether BSE infectivity is transferred directly before birth, or after birth by a variety of mechanisms, is uncertain and should be further investigated, according to the Scientific Steering Committee (SSC) of the European Commission, Directorate-General XXIV - Consumer Policy...

Whether BSE infectivity is transferred directly before birth, or after birth by a variety of mechanisms, is uncertain and should be further investigated, according to the Scientific Steering Committee (SSC) of the European Commission, Directorate-General XXIV - Consumer Policy and Consumer Health Protection. The SSC has just published its response to the question: "What is the nature and extent of the risks of vertical transmission (to include via semen, embryos or other ways of maternal transmission) of the BSE agent between cattle or between small ruminants of the same species, based on current data?" On the basis of the data currently available, the SSC concluded that: - The results of all epidemiological studies undertaken to date have been consistent with a rate of maternal risk enhancement of approximately 10 percent in the offspring of dams within 12 months of the onset of clinical signs of BSE. Where the time lapse between birth and onset of clinical symptoms is longer than 12 months, the rate of maternal transmission is reduced. Whether infectivity is transferred directly before birth or after birth by a variety of mechanisms (for example calve infection by contaminated material, environment contaminated with blood, faeces, infected feed, and so on) is uncertain and should be further investigated; - There are no scientific data to support the hypothesis that infected calves are unduly sensitive to infection on a genetic basis; - On the basis of the limited data available, it appears that there is no enhanced risk of the development of BSE in the offspring of sires who developed BSE. It is therefore unlikely that semen constitutes a risk factor for BSE transmission; - Preliminary results from an incomplete embryo-transfer study suggest an extremely low risk of transmission (95% confidence limits: 0-1.5%). These results are consistent with maternal transmission being mediated later in the gestational period either during or following birth of the animal; - Transmission of BSE by artificial insemination is unlikely for semen derived from BSE-affected bulls early in their incubation period; - Transmission of BSE via embryos is unlikely provided International Embryo Transfer Society (IETS) protocols are used. The SSC Working Group prepared a document, "Report on the possible vertical transmission of Bovine Spongiform Encephalopathy", which strongly recommended that research should be started or strengthened in fields where there were "deficits in knowledge", and that special attention should be given to: - The testing of the infectivity of semen, embryos, colostrum (the first secretions of milk after giving birth) and milk of animals of various ages, without a species barrier and via the intra-cerebral route of transfer; - Epidemiological analyses of the available data on traded semen and embryos.

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