THE BIOLOGY OF HOW MAD COW DISEASE CAN KILL HUMANS

Scientists could better gauge the risk of contracting mad cow and CJD if they knew what caused them. But no virus or bacterium has ever been associated with the diseases. The most plausible theory, then, is that the infectious protein prions wrap themselves around normal proteins in brain cells. The epidemic of mad cow disease has focused worldwide attention on the human version of the ailment, the fatal malady known as Creutzfeldt-Jakob disease (CJD). It is one of a small group of obscure diseases called spongiform encephalopathies because they produce holes in various areas of the brain, giving it a pitted appearance like Swiss cheese.

Creutzfeldt-Jakob disease, on its own, affects on average one in a million persons each year (Oldstone 163). BSE is known to have caused prion disease in several species, including domestic cats and some zoo animals. The strain variance, according to Newsweek, refers to a difference in PrP that forms on a molecular level and is reflected in differing phenotypes of clinical disease within a given species.

Unlike disease-causing viruses or bacteria, prions are normal proteins found throughout the body tissues of humans and other animals. But for reasons that are not yet understood, normal prions sometimes transform themselves into tiny particles that cannot be killed with boiling water, chemical disinfectants, or strong radiation.

These prions, almost impossible to destroy, accumulate in the brains of infected animals and people, destroying cells and leaving spongy holes in the tissue. The new variant that was killing young Britons who acquired the disease from eating cattle infected with abnormal prions from mad cow disease.

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This deadly embrace transforms the healthy proteins into more misshapen prions. They, in a lethal chain reaction, alter still more healthy proteins. The change in shape makes the proteins invulnerable to enzymes that would normally break them down. The proteins accumulate, eventually forming the clumps and holes characteristic of Creutzfeldt-Jakob. There are hints, according to Oldstone, that to contract it, you have to be genetically-susceptible (164). Thousands of patients who received infected growth hormone did not get CJD; those who did had a particular kind of brain-protein gene. But certainly, even though the fit between the protein of the human brain, it was good enough to kill more than 40 in Britain.