Mad cow disease first originated in England as a byproduct of the industrialization of cattle farming. People at the time were seeking profits and making cattle grow faster, so animal protein was used as feed for cattle to eat. The cattle themselves are herbivores, and being force-fed animal protein led to the emergence of mad cow disease. And once humans consume beef containing the virus, they can also transmit the virus to humans, causing spongy cavities in the brain of patients and symptoms such as degeneration of brain function, memory loss and confusion, which can eventually lead to death. The causative agent of mad cow disease is special and is called prion, a protein with the ability to replicate without nucleic acids, which mainly attacks brain cells.