Australia lifts the UK ‘Mad Cow’ blood ban – what’s the science?

If you lived in the UK between 1980 and 1996 there’s one thing you probably haven’t done in Australia – donate blood. It was banned in 2000 due to the potential risk of variant Creutzfeldt–Jakob disease (vCJD) – better known as ‘mad cow disease.’

Now, after modelling has shown that the risk is infinitesimally small, the ban has lifted, allowing up to 750,000 more Australians to donate blood.

But among the fanfare of new people being able to donate, the science behind vCJD, and why the ban took over 20 years to lift, is fascinating.  

“We have already had hundreds of new donors through the door in one day and look forward to welcoming many more who may be eligible for the first time in over 20 years,” says Dr Veronica Hoad, Public Health Physician at Lifeblood.

“Whilst there is a risk that further cases [of vCJD] will occur due to the outbreak in the UK, the likelihood of this occurring in Australia is much lower.”

It all started in 1984, when the first cow was recorded with Bovine Spongiform Encephalopathy (BSE), or mad cow disease. This occurred because the cows were fed contaminated meat and bone meal. After more and more cows developed the condition over the next decade, contaminated feed was stopped, and a mass slaughter of cattle was used to control the spread.

But until the mid-90s, this was seen as just a cattle disease, it wasn’t until 1995 after a 19-year-old in the UK died after an unusual six-month illness that scientists realised it could be spread to humans. The symptoms – like loss of co-ordination and memory – looked like a disease normally affecting older adults called Creutzfeld-Jakob disease.

The disease was named vCJD and it was eventually discovered that the cause was eating BSE infected meat. Two hundred and twenty-nine cases of vCJD have since been identified – the vast majority of them having lived in the UK for more than six months between 1980 and 1996.

A UK blood ban went up in Australia and a number of other countries around the world in 2000 with worries of a huge outbreak to spread.

“Although, deaths peaked in the year 2000, at the time there was high uncertainty in how many cases would occur in the future and some estimates were as high one million cases,” explains Hoad.

“Therefore, in December 2000, a precautionary ban or deferral for people that had lived in the UK for the at-risk period (six months or more from 1980-1996) was implemented for blood donation, as there was concern that cases would occur in Australia that could result in transfusion-transmission.”

vCJD is particularly tricky to catch for two reasons. The first reason is that vCJD has a long and not well understood incubation period.

Some scientists think that the incubation period could be decades, although this has seemingly not come to fruition – most of the cases occurred in the early 2000, and the amount has not shown any recent spikes.

The second reason is that the cause of vCJD and BSE is something called prions. These are misfolded proteins which can make other normal proteins also misfold. Because prions are just normal protein in the wrong form, it’s really hard to test blood to see if it’s there.

In fact, there’s still not an easy way to test large amounts of blood – like they do in blood donations – for prions.

“We have a range of tests but we look specifically for hepatitis, HIV, syphilis, and a few other things that can affect the blood supply,” says Dr Rena Hirani, a senior research fellow at Lifeblood.

“We do that testing via serology methods, or nucleic acid testing. If the tests are quite robust and reliable, those are the tests that we tend to use. Unfortunately, for prions we don’t have anything that we can use at this point.”

With this in mind, a team of researchers from Lifeblood and the Kirby Institute published a paper in Vox Sanguinis which modelled the risk of vCJD from blood transfusions in Australia. The results were incredibly positive – the risk of a vCJD transmission from a blood donation was one in 389 million, and the risk of a clinical case was one in 1.45 billion.

“The initial modelling of future case numbers early in the outbreak have not been realised and there has not been a new case in the UK since 2016 or any further cases of transfusion-transmission from transfusions this century. In addition, there has never been a case of vCJD diagnosed in Australia,” says Hoad.

“Our research demonstrated a risk of vCJD occurring once in every 65 years (but this decreases over time), or the risk being 1 in 1.4 billion transfusions. Basically, this is equivalent to a theoretical risk only and does not alter the blood safety risk in Australia.”

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