Research hints at a wider human spread of mad cow

International Herald Tribune

August 7, 2004

LONDON Scientists have found evidence suggesting the human form of mad cow disease might be hitting a wider proportion of people than seen so far, but it is possible that some may develop a milder version of the illness.

So far, autopsy tests have found mad cow, a fatal brain-wasting disease, only in people who have a certain genetic profile. However, in research outlined this week in The Lancet medical journal, scientists report finding the infection in a person with a more commonplace genetic signature and, for the first time, no symptoms of the illness.

That means that more people than previously believed could be incubating variant Creutzfeldt-Jakob disease, or vCJD, but it is unclear how dangerous such cases might be.

"Until now we had no evidence that this major subgroup was actually susceptible to vCJD infection, but this case shows that obviously they are," said James Ironside, director of Britain's national Creutzfeldt-Jakob disease surveillance unit, which conducted the study. "It's possible that the incubation period for the disease in this group will be longer than for the group we've seen clinically so far." The finding means that forecasts of how many people are likely to come down with the disease need to be radically revised, Ironside said. Even recent predictions have ranged widely, from 10 more cases to more than 10,000 cases, but those estimates have assumed that the disease strikes only those with the less common genetic profile and that the incubation period lasts up to 30 years.

"We have to be very cautious about this, and I think we have to go back and redo all the calculations based on this case," Ironside said.

The disease is believed to come from eating beef products from cows struck with mad cow disease.

Mad cow disease, also known as bovine spongiform encephalopathy, eats holes in the brains of cattle. It arose in Britain in 1986 and spread through Europe and Asia, prompting massive destruction of herds and devastating the European beef industry. Cases have also been detected in the United States and Canada.

The illness occurs when normal proteins found in the brain, known as prions, change shape and prompt adjacent healthy prions to do the same. When enough prions have done so, they deposit a plaque on the brain and surround the mark with spongy holes, killing the victim. So far 147 people in Britain, and 10 elsewhere, are known to have contracted the disease since it was first identified in humans in Britain in the mid-1990s. Five are alive. All of the people who have died so far have a genetic signature seen in about 35 percent of Caucasians.

The latest discovery was made during an autopsy of an elderly person who had died of an unrelated cause but had received a blood transfusion five years ago from a donor who later developed and died of the human form of mad cow disease. The genetic profile in this case was one that occurs in half of all Caucasians. It is less common among other ethnicities.

It is the second case linked to a blood transfusion, bolstering suspicions that the infection can be passed through blood.