Mad cow disease has been spotted in Scotland - that should reassure us all

The news that a cow in Scotland has been diagnosed with bovine spongiform encephalopathy, better known as BSE or “mad cow disease”, has reawakened the terrible memories of the 1980s and 90s epidemic .

That outbreak saw 180,000 cattle infected and millions slaughtered, but also introduced the public to the terrifying human cousin of BSE, known as variant Creutzfeldt-Jakob disease (vCJD).

Both conditions are caused by an abnormal group of infectious proteins called prions. BSE is believed to have been passed to cows from infected meat and bone meal in feed, a practice that is now banned. In rare cases, vCJD can take hold in humans who eat beef from infected cattle.

While prions are technically infectious, they are not like viruses or bacteria which may infect food, and are not destroyed by cooking and antibiotics will not cure them.

Prions accumulate in the brain and central nervous system causing irreversible damage to the neurons and leading to loss of memory, personality changes, slurred speech, blindness and spasms.

There is no treatment for vCJD and within a year of symptoms beginning most people with the disease are dead.

In May 1990, as evidence was mounting that the disease could be passed to humans, the Tory agriculture minister John Gummer held a photo-op where he fed his four-year-old daughter, Cordelia, a British beef burger to demonstrate there was nothing to fear from mad cow disease.

Now the route of infection has been established, the stunt is enough to make anyone feel queasy. As the first victims were diagnosed, many people did turn their backs on British beef and a Chinese ban on imports was only lifted in June.

Fortunately vCJD deaths are extremely rare. As of 2014 there have only been 178 cases recorded in the UK with the last reported case in 2016.

While the disease can lay dormant for many years and symptoms may never occur, meaning final numbers of infected people are unclear, scientists have stressed that the measures taken in the last epidemic have been effective.

“None of the 178 people that have been affected by vCJD in the UK was born after 1989, which is when high-risk tissues such as brain and spinal cord were banned from the food chain,” Professor Colin Smith, director of the National CJD Research & Surveillance Unit at the University of Edinburgh said on Thursday.

Which brings us back to our Aberdeenshire cow. Professor Smith and other experts have lined up to stress there is little to no risk of this case having any impact on human health.

The cow was diagnosed with “classical BSE”, which is the form acquired by contaminated food, but it’s not clear if it’s an old cow, who may have been infected by contaminants left over in a field or trough or a younger one, in which case the feed bins and other cattle may be infected.

Tests are currently underway to identify this route of infection and any other cases in this herd or relatives.

But these sporadic BSE cases are not unexpected at the tail end of an outbreak. The World Organisation for Animal Health reports that fewer than 10 cases have been diagnosed every year since 2010, though this has trended down and there were none in 2016.

This downward trend, and the latest detection in Scotland, are signs the screening protocols that curtailed the last epidemic are still working as expected and vigilance has not dipped in recent decades.

"To me this means that the surveillance that has been in place for quite a few years is actually working," Dr Steven van Winden, a lecturer at the Royal Veterinary College said.

The British public, and especially Michael Gove’s children, can rest easy.