BSE and vCJD FAQ

So what is BSE?
Better known as "mad cow disease", it stands for Bovine Spongiform Encephalopathy. It's a neurodegenerative disease which gradually destroys cattle brains by turning them spongy. Cattle with BSE stagger around and eventually lose all coordination. Since the first officially documented case in 1986, around 180,000 cows have died of the disease in Britain, the worst affected country. Millions more have been slaughtered to eradicate suspect herds. BSE is now on the wane in Britain, down to a few hundred cases from a peak of around 37,000 in 1992. But cases are on the rise in mainland Europe.

What about vCJD? What's that?
vCJD is the human equivalent of BSE, and stands for "variant Creutzfeldt-Jakob Disease". After examining brains from young patients who'd died of a strange and distressing new form of dementia in the mid-1990s, doctors in Britain established and announced in March 1996 that BSE and vCJD were one and the same, albeit affecting different species. Brains from the patients had the same spongy appearance as the cattle brains. Later experiments in mice proved that the same "prion agent" causes both diseases.

What's a "prion"?
Prions are mutated versions of a normal protein abundant in brain and nerve cells. No-one knows the true function of the normal prion protein, called PrPC, which sits on the surface of cells. But simply through physical contact, the mutated prion protein (called PrPSC) is able to switch the normal version into the mutated form. Brain and nerve cells clog up with the abnormal prions, die, and disgorge their prions. These infect healthy neighbouring cells. Eventually, the whole brain becomes filled with plaques of the abnormal protein, holes forming where cells have died en masse.

So where did BSE come from?
An official report into BSE published in October 2000 favours the idea that it started in a single cow which developed the disease spontaneously through a unique, random mutation in its PrPC gene. When other cattle ate the ground-up remains of this cow, they developed the disease too. The disease escalated as more and more cows ate infected feed and had their infected remains fed to yet more cows. Originally, scientists suggested that the disease originated when cows ate feed containing an unusual form of scrapie, the sheep equivalent of BSE. Now, ironically, the scrapie theory is gaining favour again.

How did BSE spread to humans then? Was it meat?
That's the 6-million-dollar question! Although no-one has proved it, most experts suspect that it spread to us when we ate meat products infected with prions. Researchers have now established how the prions are absorbed across the gut wall into the lymph system. After a few years of silent incubation they eventually reach the brain and cause vCJD, which is when the disease first becomes obvious.

So millions of us must have been infected years ago before anyone had heard of BSE?
Hopefully not, but no-one knows. When BSE was discovered in 1986, hardly anyone believed that it could spread to humans. But scientists soon discovered that BSE was spreading from cow to cow in meat and bone meal (MBM), a protein-rich ingredient of animal feed made by grinding up the unwanted remains of sheep and cows. So in 1988, the government banned farmers from feeding cows or sheep with MBM. The idea was to stop prion-riddled MBM being fed to healthy animals, breaking the chain of infection. Mainland Europe introduced similar measures in 1994.

Hang on. What about us humans?
Yes, sorry. Save for a few siren voices, no one believed BSE would spread to us. The rationale was that for 250 years, Britons had eaten lamb without catching scrapie, a counterpart prion disease that affects sheep. If we don't get scrapie from sheep, scientists reasoned, we won't catch BSE from cattle either. But as a precaution, the government decided in 1989 to ban from human food the most prion-rich cattle tissues, such as the brain and spinal cord. But not until 1995 did the government ban from human food a potentially infectious paste called mechanically recovered meat, or MRM. This was produced at abattoirs by mechanically dislodging scraps of meat from spinal columns of cattle, producing a slurry which food producers added to products such as meat pies and patties. The pastes included nerve tissue called "dorsal root ganglia" which were subsequently shown to be highly infectious, so many people may have eaten suspect material right up to 1995. Then came the bombshell in March 1996 that BSE could indeed spread to humans. The cosy assumptions about scrapie had been shattered.

Well, what's going to happen to us?
Again, no one knows whether there'll be an epidemic of vCJD, or how big it will be. Or whether it will come in waves several years apart. Optimists hope that the early precautions might have saved millions of people. They hope that the present wave of vCJD has already peaked at just over 100 deaths and that will be that. Pessimists predict that thousands will die, possibly in waves to come.

Why would it come in waves? Why wouldn't we all die at once?
Assuming it spread in food, we all had different "doses" depending on our diet, and no-one knows how much it takes to kill a person. We do know it only takes a peppercorn-sized dose of infective material to give a cow BSE. But it's difficult for epidemiologists to predict how many people will die when they don't know how much infective material we ate individually or collectively, or when. Also, it may be that some of us are protected by our genes. It turns out that all the victims of vCJD so far have inherited a particular signature of the PrPC gene, called MM. In Britain, 37 per cent of the population have this signature. Encouragingly, half the population (51 per cent) have a different signature, called MV, and another 12 per cent have a variant called VV. So it may be that MMs are the only ones at risk, but most of them are resistant anyway. The others can't relax, however. It may simply be that the MVs and the VVs have longer incubation periods and are fated to succumb later in life.

Is there any other way we could have been infected?
Prions survive most routine disinfection procedures such as steam sterilisation. Some scientists have warned that prions might spread between hospital patients aboard surgical instruments unknowingly used previously on patients with vCJD. To counter this, the government last year ordered surgeons to use disposable instruments for removal of tonsils - organs known to harbour prions. They might also spread in blood transfusions, but there's no evidence for this.

Obviously, since BSE originates in cattle, beef and products containing it such as pies were the prime suspects before all possible routes of infection were closed. But British beef is now probably among the world's safest, and has been for some time. There have been question marks about sheep, however, with suspicions that BSE might have crossed undetected into sheep during the 1980s before the ban on MBM came into force. UK government scientists have been testing material from sheep that died from scrapie at the time to see if they really died of BSE. Encouragingly, no cases have been reported yet. All other meat is thought to be safe to eat, from pork and venison through to chicken and quail.

Are we sure prions cause vCJD?
The evidence is pretty strong. But there are other theories. One holds that a bacterium causes the disease by triggering the body to attack itself. This "autoimmune" theory has been dismissed on the grounds that some lab mice still get a form of BSE even though they lack an immune system. Another alternative is that cows developed BSE after exposure to organophosphate pesticides. The geographical pattern by which the disease spread doesn't support this, although one experiment showed that cells exposed to the OP Phosmet are easier to infect with prions.

Is there any hope of a cure?
Researchers are working on it, and there's been encouraging progress. A female patient treated in the US with a combination of quinacrine, an anti-malaria drug, and chloropromazine, an anti-schizophrenia drug, made good progress recently, but there's no proof she has vCJD. Another patient receiving the same treatment got worse. Recent experiments on animals have raised the hope that vaccines might be possible, priming the body so that it produces antibodies which block physical contact between mutated prions and normal proteins. Recently, the British government stepped up efforts to identify potential drugs.