1/13 Mad Cow Disease
This disease, officially known as Bovine Spongiform Encephalopathy, effects the nervous system in cattle and is caused by proteins called prions infecting the brain. it devastated the United Kingdom's beef industry in the late 1980s and early '90s, leading to a ban on exporting the meat for years. What made it even worse was that infected beef was also found to cause a strain of Creutzfeldt-Jakob disease in humans.
The outbreak killed around 200 people around the world. And, the crisis was caused by human error. Cattle were actually fed infected carcasses which led to the disease spreading. Lax slaughtering practices then resulted in nervous tissue being mixed with lower-quality meat products like hamburgers, allowing it to infect humans.