Silent Mad Cow

Drs. Norbert Herzog & David Niesel

Drs. Norbert Herzog & David Niesel

Medical Discovery News

Ten years after bovine spongiform encephalopathy (BSE), commonly called mad cow disease, was diagnosed in cattle in Britain, the British government admitted that it could be transferred to humans in a new form called variant Creutzfeldt Jakob disease (vCJD).

Cases of BSE spread to cattle in other countries, and more people in different countries were being diagnosed with vCJD. By 2004, the U.S. had passed various laws to eliminate BSE-infected cattle from the market. However, to this day, there are still sporadic reports of cows diagnosed with BSE both in the U.S. and abroad.

BSE and vCJD are neurological diseases that arise from prion plaques that form in the brain. Prions are simply misfolded proteins. This can be caused by a genetic mutation, spontaneous misfolding, or consuming infected beef. These misfolded proteins can convert healthy or normal proteins into misfolded ones. Once they appear, abnormal prion proteins aggregate, or clump together. Investigators think these protein aggregates may lead to loss of brain cells and other brain damage. Areas of the brain’s grey matter are slowly displaced and the brain develops holes or a spongy appearance, hence the name spongiform. There is no treatment or cure and eventually the damage is severe enough to lead to death.

Initially cattle acquired the prion proteins in feed supplements made from infected sheep brains and spinal cord tissues. Once regulators understood the source, they passed laws banning the process of feeding dead animals to livestock. Unlike meat contaminated with bacteria, cooking does not destroy prion proteins. In an effort to eliminate prions from the food supply, the U.S. Department of Agriculture has imposed a rule that the brains and spinal cords of cattle must be removed prior to processing into edible meat.

There have been 175 people in Great Britain diagnosed with vCJD and an additional 49 people in 11 other countries. A large study indicates that 1 in 20,000 people in Britain (30,000 total) carry the misfolded prion proteins and are at risk of developing vCJD. These new results suggest that many people in Britain may be carrying the prions but are symptomless, at least for now. This could also mean that these cases are silent carriers, who will not develop clinical vCJD. It remains a mystery that only time and additional studies will solve.

Since there is no blood test for vCJD, carriers could unwittingly pass on this disease to others when they give blood. Earlier research suggested that the incubation period for vCJD was about eight years, but now scientists think that there are at least three types of the misfolded prion proteins, with different incubation periods and different types of prion disease.

Blood tests need to be developed to protect against the inadvertent transmission of vCJD. Better farm and food practices and laws will also help eliminate other sources of prion disease. Scientists in a number of countries are exploring potential treatments for these disorders.

Medical Discovery News is a weekly radio and print broadcast highlighting medical and scientific breakthroughs hosted by professor emeritus Norbert Herzog and professor David Niesel, biomedical scientists at the University of Texas Medical Branch at Galveston. Learn more at www.medicaldiscoverynews.com.

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