Mad cow disease is down but not out. A case of bovine spongiform encephalopathy (BSE), the cattle infection that causes the lethal human brain disease vCJD, in the UK. The cow had died unexpectedly on a farm in Aberdeenshire, Scotland, so was tested under routine surveillance procedures.
鈥淭he BSE case is a very unwelcome development of course, but not a complete surprise. The positive angle to this story is that our surveillance system is working,鈥� says Mark Woolhouse聽at the University of Edinburgh.
That cow, its offspring and any cattle of the same age on the farm have since been destroyed, meaning the 鈥減rion鈥� 鈥� the misshapen protein that causes BSE 鈥� has been contained. But the case, 10 years after the last mad cow in Scotland, is a reminder of how BSE can lurk undetected, even when the cattle feed that spreads it is controlled to prevent prion contamination, and countries are actively on the lookout for fresh cases.
Advertisement
Lurking cases
The case itself is not surprising: found that BSE could linger on in British cattle until 2025, with a few cases a year despite feed controls. Overall the BSE picture is actually looking good in the UK, where the disease began.
However, many of the UK animals that have tested positive for BSE in recent years were infected by prions that arise spontaneously among cattle, rather than the prions that cause vCJD. The latest case was the second kind: it was what is now called 鈥渃lassical鈥� BSE, which has so far killed more than 220 people worldwide. There have only been 76 classical BSE cases detected in the European Union since 2010.
Although the rate at which new ones appear is steadily falling, additional cases could be lurking 鈥� partly because BSE is so hard to spot. In 2016, the EU tested more than 1.3 million cattle and found only five cases. All were in France or Spain, and only one of these was classical. What鈥檚 more, tests of EU cattle have revealed that the 2016 classical case, like the Aberdeenshire case, arose despite the affected cow being born after the elimination of contaminated feed. This raises the issue of whether countries are doing enough to catch new cases of BSE.
Variable vigilance
Within the EU, vigilance varies greatly, and the countries that recently detected cases have surveillance systems that are nine times as effective as those in countries that haven鈥檛 found any, according to the European Food Safety Authority.
Moreover, infected animals and feed were shipped worldwide to places including Russia, Indonesia, India, and Saudi Arabia, but few of the countries who bought them have yet reported BSE, and none do much surveillance. All fear the long-term loss of beef exports that follows the discovery of BSE: China started buying British beef again only this year.
Of these countries, only Canada, Japan, the US and Israel have reported any mad cows. Japan tested 1.6 million cattle to find its 36 cases. Although the US slaughters 35 million cattle a year, it tests only 40,000, and has only detected one home-grown case so far.
William Hueston of the University of Minnesota says he fears that as memories of BSE fade, some countries might start feeding cattle remains to cattle again, thinking they are prion-free. It could take time to spot any trouble. Research suggests that even the best EU surveillance practices would take 15 years to detect a nascent epidemic if one started unexpectedly, for example in the US. During that time, people would have eaten thousands of infected cattle.
So reports that BSE is 鈥渁lmost extinct鈥� could prove premature. Scotland鈥檚 case this month could be one of its last 鈥� but it might just be the tip of an iceberg.
