A phrase like “mad cow” is sure to whip up a media frenzy. When the USDA confirmed last week the first case of bovine spongiform encephalopathy (BSE) in six years, news headlines were splashed with reports of “mad cow disease,” the informal and scarily evocative term for BSE. What got lost in these initial reports is that this case of BSE involves a different protein than previous epidemics in Europe, and there’s no evidence that this type is transmissible to humans.
Nature News has a solid and thorough explanation of the science behind this case of BSE, known as L-type. As it happens in nature, mutations arise spontaneously, and L-type BSE is caused by a spontaneous mutation in a particular protein. A lot is still unknown about L-type, but we have never seen it spread through cow populations (or jump to humans) through ingestion. Previous BSE epidemics in Europe were spread by the admittedly gruesome practice of grinding up leftover cow parts and feeding them back to cows, but this has been long banned in the United States because of BSE. Critics have argued that there may still be indirect sources of cow protein in feed (cow protein is fed to chickens, and poultry leftovers go back into cow feed), so more stringent regulations are needed.