When your blood eats your brain

Mad-cow disease has shut down Britain's blood supply. Could it also be contaminating the US supply?

Mad cow disease may seem like a vegetarian plot to scare everyone else off from eating flesh, but recent news from Britain gives beef eaters and tofu fanciers alike something to worry about. On February 26, the British government took the extraordinary step of banning all British blood products for domestic use to prevent the spread of "new variant Creutzfeldt-Jakob disease" (nvCJD), the fatal brain-wasting illness thought to originate from mad cows ("Mad Cows Ate My Brain" SW, 3/12/98). British medical authorities defend the safety of UK blood and deem the action "a precautionary measure" to guard against a "theoretical risk." While the Brits' blood ban may be purely preventive, it does raise questions about whether similar dangers, theoretical or otherwise, exist in the American blood supply.

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New variant Creutzfeldt-Jakob disease and the native human form of the illness, classical Creutzfeldt-Jakob disease (CJD), are members of a family of illnesses known as transmissible spongiform encephalopathies (TSEs). Scientists suspect TSEs are caused by rogue proteins dubbed prions, which can sporadically develop a pathogenic form, burrowing microscopic holes in victims' brains and causing progressive dementia and, ultimately, death. All else being equal, TSEs occur at a uniformly low rate of about one to two cases per million in all mammals. However, prions can be spread through ersatz cannibalism—fattening food animals on members of their own species—or via surgical transplants of infected human organs.

Though prions concentrate in the brain, they also show up in blood. That led the US Food and Drug Administration (FDA) in 1995 to institute a blood-donor screening policy to prevent CJD—which is thought to strike between 250 and 500 Americans each year—from spreading through the US blood supply. Currently, blood banks must refuse donors at risk of developing CJD. Blood and plasma products donated by people who later develop the illness must be destroyed.

The policy is conservative, says Paul Brown, a prion researcher at the National Institutes of Health. "In spite of intensive study, there is not a single documented instance of blood causing the disease," he says. Brown acknowledges, however, that researchers have been looking for a blood-CJD link for only the last five years. Those efforts are complicated by the 10- to 40-year incubation period for the disease and the lack of a blood test to diagnose the illness.

Studies by Brown and other researchers have shown that blood can transmit infection between laboratory animals, albeit at very low levels. While that probably holds true for humans, too, blood is not a terribly efficient means of spreading infection. "The probability of someone receiving a [contaminated] blood product and getting infected is for the most part unknown," says Brown, "It's very small. Probably not zero, but it might be zero."

Research under way at several laboratories will help define the actual risk presented by CJD-infected blood, according to Dr. Brown. In the meantime, the FDA's blood policy is designed to keep contaminated blood from reaching the public.

But that is easier said than done. Since late 1996, the FDA has recalled 34 blood products because donors subsequently developed CJD or were identified as being at risk of developing the disease. However, it's doubtful that health officials are catching all the blood donors incubating deadly prions. The system relies on relatives reporting a donor's disease to the blood collection agency, although there's little public knowledge of the risk to blood. Moreover, a patient's blood may be infectious for a decade or more before symptoms appear. By the time CJD is diagnosed, blood donations may be long gone.

Even if next-of-kin reporting were reliable, says Michael Hansen, a research scientist with the Consumers Union, CJD appears to be commonly misdiagnosed as Alzheimer's disease, other dementias, and even psychiatric conditions. Preliminary studies suggest that as many as 13 percent of the nation's 4 million Alzheimer's patients may actually be suffering from CJD. If true, Creutzfeldt-Jakob disease is a much more common illness than scientists believe, says Liz Armstrong, co-founder of CJD Voice, a national support group for families of CJD victims. The number of blood donors harboring the dangerous prions in their veins, therefore, could be larger as well.

Concern over prions lurking in the blood affects a population broader than the 4 million Americans who receive blood transfusions each year. There are some 33 blood products "fractionated" from whole blood, including clotting factors for hemophiliacs, immunoglobulins for shock victims and immune-depressed patients, and albumin, which is used in common vaccines such as those for polio and hepatitis B.

While the risk of infection from a contaminated product may be small, as the NIH's Paul Brown believes, the idea of prions in your plasma products is an unsettling one. A Florida couple recently filed a lawsuit against their fertility clinic, claiming the wife was exposed to CJD from a contaminated plasma product used to store the woman's eggs. Liz Armstrong tells of another woman whose children recently received a rabies vaccine later found to be contaminated by a CJD patient's plasma.

While the benefit of preventing life-threatening illnesses such as rabies undoubtedly outweighs the supposedly low risk of developing CJD, that calculation doesn't hold for all plasma products. Armstrong worries about her own young children, who by Illinois law must be vaccinated against hepatitis B (also required for Washington schoolchildren), which contains albumin. Since her father died of hepatitis B, there's a genetic risk factor in her family, she says. Her children, however, are not in a high-risk category for the disease. "Their grandfather just died from CJD," she says. "By giving my children this vaccine, can you assure me they're not going to die from CJD? The risk does not outweigh the benefit."

One risk that isn't being considered by the FDA is that posed by the new variant CJD that jumped from British beef to Britons. While the size of the Brits' human epidemic is unknown, and may remain so for decades, 80,000 Britons are conservatively estimated to be incubating the disease, with other predictions running into the millions. That's one reason the British no longer trust their own blood.

The FDA's current policy doesn't exclude blood donors who lived in the UK during the 1980s and 1990s when contaminated British beef was sold to an unknowing public. Tens of thousands of American military personnel stationed in England and Europe at the time were regularly fed British beef until the military stopped buying it in March 1996, after the UK government revealed the dangers of mad meat.

Should past consumption of British beef during the UK's bovine spongiform encephalopathy epidemic disqualify you as an American blood donor?

The chances of an American "eating [British] hamburger and coming back home and contaminating the blood supply . . . is so improbable that it's close to zero," says the NIH's Paul Brown. But he appends two caveats: The British epidemic may grow ("They may have thousands and thousands of cases, in which case the risk is greater"); and nvCJD may carry greater infectivity in blood. Unlike garden-variety CJD, prions that cause the new variant can be detected on a patient's tonsils—indicating a greater presence in the blood's immune cells.

Related Links and information:

Previous Carrel Article on Mad Cow Disease

 
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