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UNTANGLING THE DEADLY "MAD COW" MYSTERY
           International Herald Tribune by Barry James December 7, 2000

PARIS Nobody knows how it started. Nobody knows how it will end. Nobody knows how many people eventually will die from it. Those are among the frightening mysteries scientists are discovering about "mad cow" disease, or BSE, the bovine form of transmissible spongiform encephalopathy.

The disease can arise out of nowhere and lie dormant for years, which the official British BSE Inquiry believes is how it started in England.  Perhaps only one cow spontaneously developed the disease at first.  To become an epidemic it needed an amplifier, which in Britain was the practice of feeding grazing animals the ground-up remains of others of their species.

In Europe, 91 people are known to have contracted variant Creutzfeldt Jakob disease, the fatal neurodegenerative affliction that humans can develop when exposed to infected meat. Creutzfeldt Jakob disease, which leads to dementia and eventually leaves the brain pitted with holes and resembling a sponge, was first identified independently by two German doctors in the 1920s, but until recently it was a condition of the elderly. Variant Creutzfeldt-Jakob disease also attacks younger people, some of them in their teens.

The human toll might seem small when compared with diseases like malaria, which kills millions of people every year. But the prospect of turning loose a stealthy, deadly and largely unknown pathogen is what most concerns scientists across Europe. The mad cow scare has touched off a panicky reaction against eating beef, but the worrisome fact is that many people already may be infected, perhaps because proteins known as prions that had somehow become aberrant were lurking in their baby food or hamburger many years ago.

The danger to humanity, scientists say, is that the general level of potential infection will rise, making it easier for the disease to emerge in future generations. This threat is illustrated by the speed at which bovine spongiform encephalopathy amplified among cattle in Britain in just a few years. There have now been more than 180,000 cases, with many others doubtlessly undiscovered among the 4.8 million cows culled and destroyed since 1996 in an attempt to check the disease. An article in the science journal Nature estimated that 975,000 infected
cows entered the food supply.

Here is a chilling catalogue, drawn from two dozen interviews with experts and a review of scores of scientific documents, including Britain's recent 16-volume official BSE report, which illustrates why scientists are so concerned about BSE and related spongiform diseases that can affect most species of mammals and birds:

The pathogen that wipes out memory, personality and physical functions is extraordinarily tenacious. It resists heat, alcohol, boiling, ultraviolet light and ionizing radiation. Surgical instruments that come in contact with it can remain contaminated after normal sterilization procedures, and researchers don body protection before handling it.

The pathogen can survive years of being buried in the soil, which is>worrisome given that cattle remains often end up in landfills. Iceland in the 1950s slaughtered all its sheep to eliminate a related disease called scrapie. When it brought in healthy animals, scrapie soon reappeared. Some scientists believe that scrapie can mask low levels of BSE in sheep.

While they take time to emerge, perhaps over many decades in humans, the spongiform diseases are highly infectious. According to British scientists, a cow can get BSE by eating one gram of infected material -a speck the size of a peppercorn - from another cow. Even a minute trace of the material in meat and bone meal, the protein supplement produced from rendered animal remains, can infect a cow.

The European Union's Standing Scientific Committee says that "the minimal infective dose considered to be valid for animals should also be applied for humans." Nobody knows what a minimal dose is, but British scientists discovered that a piece of wire that had been in contact with the pathogen for five minutes became as infectious as a solution made from infected brain.

Although the spongiform diseases are most infectious among members of the same species, they can jump the barrier to other species with varying levels of ease. Much has still to be learned about this species barrier, particularly so far as humans are concerned. Scrapie, for example, is believed not to infect humans. But in the United States, doctors identified several cases of variant Creutzfeldt Jakob disease among people who had eaten squirrel brains, and scientists warn that a spongiform encephalopathy called chronic wasting disease, found among deer and elk in the United States, is another potential threat to
humans.

Once the pathogen has adapted to a new species, it can infect other members of that species with a much lower dose. In zoos, the pathogen has caused an outbreak of spongiform diseases among primates, big cats, antelope and other species, through the feeding of infected material.  One study last year identified 82 cases in zoos. Bovine spongiform encephalopathy can be experimentally provoked in sheep, and domestic cats have acquired a similar encephalopathy from pet food. A 12-year old lion in the Newquay zoo in England was put down recently and found to be suffering from a form of transmissible encephalopathy.

The spongiform encephalopathies are surreptitious. An animal can harbor a spongiform disease and show no symptoms. Mice infected with hamster prions remain apparently healthy throughout their normal life span, but in fact become highly infectious. Cattle are believed to be infectious at an early stage of incubation as the disease spreads through the central nervous system toward the brain, the most lethal tissue of all.  Because the incubation period in cows is thought to be longer than three years, the European Union this week decided to destroy cattle for market older than 30 months unless tested after slaughter and found to be free of BSE.

The possibility that an animal can be infectious and show no symptoms raises the question whether people can as well. Scientists fear, for example, that a patient with undetected Creutzfeldt-Jakob disease who was undergoing surgery treatment for another disease might pass it along through surgical instruments. Since nobody knows the average incubation period in man, blood transfusion services in several countries, including the United States and Canada, are turning away donors who have lived in Britain although it is not certain that the defective prions can be passed on through blood.

When the mad cow epidemic emerged in Britain in the 1980s, Stanley Prusiner, a U.S. neurologist and Nobel laureate, had already published his findings that the spongy condition of victims' brains was caused by "proteinaceous infectious particles," or prions. Proteins are the body'sprimary component and the basis of all enzyme reactions. As they are produced, they fold or coil three-dimension ally.

The agent that causes spongiform disease is a protein that has folded wrongly, and which is able to pass this defect to normal proteins. Because the defective prions resist breakdown by enzymes, they build up within nerve cells and eventually the brain.

The Prion Principle
It is as though bricks told an architect how to build a house. KurtVonnegut described the prion principle in his novel "Cat's Cradle," in which a crystal of Ice-IX "taught the atoms the novel way in which to stack, lock and crystallize" until the oceans turned to ice.  Unlike viruses, proteins contain no genetic material and therefore provoke no immune response. This is why it is so difficult to detect prion disease in a living being. A brain or tonsil biopsy might findCreutzfeldt-Jakob disease in a human, for example, but only if doctorsexamine an infected part.

The defective proteins survive the rendering process that turns an animal's carcass into industrial fats and gelatin on the one hand, and meat and bone meal on the other. The meal is an effective and cheap protein that helps animals grow and produce milk. When it became apparent that turning herbivores into carnivores was the likely cause of BSE, Britain forbade feeding ruminant meat and bone meal to cattle in 1988, but continued to export the material, thus spreading the disease to other countries.

Scientists consider the inexpensive meat that comes from old dairy cows to be the most dangerous. It is pooled in beef patties, meat pies and pasta fillings; meat from as many as 60 animals may go into a hamburger mix. Some of the cheapest meat is stripped by machines and high-pressure jets from the bone, which is likely to be highly infectious in a sick cow. Each cow provides about seven kilograms (15 pounds) of machine-recovered meat that is incorporated into five- to seven-ton batches of material. The EU's standing scientific committee estimated                                    continued
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that each batch contains meat from about 1,000 animals, any one of which could infect the whole, and expose as many as 400,000 persons to the agent.