BSE has been shown to spread naturally between sheep for the first time. It passed from mother to lamb, before or during birth, in an experimentally infected flock. But if the study shows the infection spreads more generally within the flock, that means BSE could still be lurking in Europe’s sheep, possibly posing a greater health risk to people than that from “mad” cows.

Scientists found in 1996 that sheep develop a disease similar to BSE if they eat infected cattle tissue. But feeding cattle remains to sheep was banned in Britain in 1988, and in the EU in 1994. All the sheep infected before then should be gone by now.

So there should be no more BSE sheep – unless they can transmit BSE to each other. Cattle cannot do this, but sheep transmit a related disease called scrapie between themselves, apparently when they eat placentas and other birthing remains in the field. If BSE also spreads “horizontally” in this way – between other members of the flock – it might have kept spreading in sheep even after the feed ban.

And because the symptoms of BSE in sheep resemble scrapie, “mad” sheep might not have been noticed. Nearly 2700 sheep with apparent scrapie have now been tested for BSE in the UK. None so far had clear BSE, though two are being tested further. BSE-infected goats, which are biologically similar to sheep, were found in France and possibly the UK in 2005.

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Source: New Scientist, Deborah MacKenzie
August 17, 2005

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