Two new strains of mad cow disease, the brain-destroying killer linked to rogue proteins known as prions, turned up this year in Europe. Even more worrisome, the molecular signature of one new strain resembles a deadly human neurological disease, sporadic Creutzfeldt-Jakob, leading to speculation that the new form of mad cow disease could spread among humans through the consumption of tainted beef. That’s just what happened with the older form of mad cow disease, which first came to light in the 1980s and led to the destruction of millions of cattle in Britain and Europe. About 150 people, mostly British and more than half under age 30, died after catching the disease—now known as variant Creutzfeldt-Jakob—by eating beef.
In January French scientists reported in the journal of the European Molecular Biology Organization that they had identified prions with unusual features in 3 out of 55 animals with mad cow disease. The next month, in the Proceedings of the National Academy of Sciences, a team of Italian researchers reported a third strain of mad cow in 2 out of 8 afflicted animals. That variety cropped up in a different part of the brain than the other strains, and it also produced clumps of proteins akin to the amyloid plaques found in sporadic Creutzfeldt-Jakob disease, a fatal brain disease of unknown origin that usually affects those over age 55.
Cases of sporadic Creutzfeldt-Jakob are extremely rare. But a few autopsy studies conducted over the last 15 years suggested that the disease might be far more common than was previously thought; in one account, up to 13 percent of cases pegged as Alzheimer’s were actually Creutzfeldt-Jakob. “Whether that means there’s a connection between the human form of sporadic Creutzfeldt-Jakob and the new strain of mad cow is a completely open question, but the fact that we see similar damage is intriguing,” says Michael Hansen, the senior research associate for Consumers Union, a nonprofit consumer advocacy group. And some cases of mad cow may have gone undetected because scientists examined only certain portions of animals’ brains for signs of infection, Hansen says. “The big question is, where did these other strains come from?”
Meanwhile, the first known case of mad cow disease in the United States was reported in late December 2003 in Washington State.