Other forms: prions
In microbiology, a prion is a tiny particle, a misshaped protein that causes a particular type of disease. Prions are the cause of many brain illnesses in humans and animals.
So-called mad cow disease is caused by prions, as is chronic wasting disease, which affects deer, and Creutzfeldt-Jakob disease in humans. These are all extremely serious illnesses that aren't fully understood by scientists. Prions are pathogens, like viruses and bacteria, but they exist as proteins within normal cells. It's only when they become strangely folded that they begin to infect the proteins around them, ultimately causing brain damage. The word was formed in the 1980s, from pro(teinaceous) in(fectious particle).