Education And Debate

The myth of maternal transmission of spongiform encephalopathy

BMJ 1995; 311 doi: (Published 21 October 1995) Cite this as: BMJ 1995;311:1071
  1. R M Ridley, head, MRC comparative cognition teama,
  2. H F Baker, senior scientific officera
  1. aDepartment of Experimental Psychology, Cambridge University, Cambridge CB2 3EB
  1. Correspondence to: Dr R M Ridley, Innes Building, School of Clinical VeterinaryMedicine, Cambridge CB3 0ES.
  • Accepted 8 September 1995

It has long been accepted that the pattern of occurrence of scrapie—the form of spongiform encephalopathy associated with sheep—is determined mainly by maternal transmission, and this view has had a profound influence on policy decisions in the control of bovine spongiform encephalopathy and on public concern over the risk to human health from this disease. The occurrence of maternal transmission is, however, not predicted by modern knowledge of the aetiology of spongiform encephalopathy, and even though claims of maternal transmission have been reiterated frequently in the literature, re-examination of the source data reveals that these data are extremely scanty, unreplicated, and probably subject to ascertainment bias. The probability of maternal transmission of spongiform encephalopathy in any species should be viewed with the greatest scepticism.

In assessing the risk to human health of the epidemic of bovine spongiform encephalopathy (BSE) in the United Kingdom, the Southwood Committee accepted the view that in scrapie (the spongiform encephalopathy occurring in sheep) “there is transmission of scrapie from the infected ewe to lamb.”1 Maternal transmission means the infection of the lamb by the dam through a mechanism which is specific to this biological relationship—prenatal or perinatal transplacental transfer of infective agent or infection through milk, saliva, or the close contact of birth and suckling. The House of Commons Agriculture Committee on BSE concluded that if maternal transmission also occurred in bovine spongiform encephalopathy then “its elimination will be much harder and its implications for humans much more uncertain” and “the policy implications would be substantial.”2

In 1989 a long term study was initiated to monitor the possible occurrence of maternal transmission in bovine spongiform encephalopathy.3 Alarm in the general public was fuelled by Professor Lacey, who promulgated the view that for bovine spongiform encephalopathy “vertical transmission should prolong the epidemic into …

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