The disease may be most easily transmitted to human beings by eating food contaminated with the brain, spinal cord or digestive tract of infected carcasses.^[3] However, the infectious agent, although most highly concentrated in nervous tissue, can be found in virtually all tissues throughout the body, including blood.^[4] In humans, it is known as new variant Creutzfeldt–Jakob disease (vCJD or nvCJD), and by October 2009, it had killed 166 people in the United Kingdom, and 44 elsewhere.^[5] Between 460,000 and 482,000 BSE-infected animals had entered the human food chain before controls on high-risk offal were introduced in 1989.^[6]

A British and Irish inquiry into BSE concluded the epizootic was caused by cattle, which are normally herbivores, being fed the remains of other cattle in the form of meat and bone meal (MBM), which caused the infectious agent to spread.^[7][8] The cause of BSE may be from the contamination of MBM from sheep with scrapie that were processed in the same slaughterhouse. The epidemic was probably accelerated by the recycling of infected bovine tissues prior to the recognition of BSE.^[9] The origin of the disease itself remains unknown. The infectious agent is distinctive for the high temperatures at which it remains viable, over 600 degrees Celsius (about 1100 degrees Fahrenheit).^[10] This contributed to the spread of the disease in the United Kingdom, which had reduced the temperatures used during its rendering process.^[7] Another contributory factor was the feeding of infected protein supplements to very young calves.^[7][11]