Scientists have found evidence suggesting that the human form of mad cow disease might be infecting a wider group of people than seen so far and that some may develop a milder form of the illness.
Since variant Creutzfeldt-Jakob disease was first identified in 1996, little has been learned about it. Until now, the fatal brain-wasting disease was found only in people who have a certain genetic profile.
But research published this week in The Lancet medical journal reported the infection in a person with a more common genetic makeup and with no symptoms of the illness.
That means more people than previously believed could be incubating the disease, thought to come from eating processed beef products from cattle infected with mad cow disease, or bovine spongiform encephalopathy. It also raises the possibility that some people may get only a mild infection, as opposed to the fatal disease.
Scientists don’t know how many people are infected with the human form of mad cow disease. Projections vary wildly — from just 10 more cases in the future to hundreds of thousands — because so many factors that play into the disease remain a mystery and because there have been so few cases to study.
Experts don’t know how long the incubation period is; whether everybody is equally vulnerable; exactly how the disease spreads and whether it can be easily passed on before symptoms develop. There is no test to diagnose it, no treatment and no cure.
Forecast revisions needed
The latest finding means that forecasts need to be radically revised because they were based on the assumption that the disease only affects people with a particular genetic profile found in about 35 percent of Caucasians, said James Ironside, director of Britain’s national Creutzfeldt-Jakob disease surveillance unit, which did the study.
In new research, an autopsy found the disease in a person whose genetic signature is shared by about 50 percent of Caucasians.
Ironside said, “I think we have to go back and redo all the calculations based on this case.”
So far, 147 people in Britain, and another 10 elsewhere, are known to have contracted the disease. Five are still alive.
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 are altered, they deposit a plaque on the brain and surround the mark with spongy holes, killing the victim.
Possible mild case
The latest discovery was made during an autopsy of an elderly person who died of an unrelated cause but who had received a blood transfusion five years earlier from a donor who later died of the human form of mad cow disease.
Strangely, the infection was found only in the spleen, but not in the brain or other places the disease typically turns up. It is unknown whether the disease might eventually have killed this person after a longer incubation period or whether the infection was milder and may have done no harm.
Dr. Kumanan Wilson, a blood safety expert at Toronto General Hospital in Canada, said the finding is a vindication of policies by some countries that have taken steps to protect against what was previously a theoretical risk of spreading the disease through blood transfusions. During the HIV epidemic, the blood supply wasn’t protected until HIV began spreading through transfusions.
“By acting in advance of complete certainty, policy makers have potentially protected against vCJD emerging as a new large-scale blood-borne epidemic,” said Wilson, who was not connected with the study.