Delusional infestation (DI) is a rare and bizarre condition. Patients are utterly convinced they are infected with living or inanimate pathogens (think: worms, insects, and fungi) when, in reality, there is nothing there.
It can be debilitating and scary, and now, it appears, more common than previously thought. A report published in JAMA Dermatology estimates that 27.3 people per 100,000 (0.027 percent) suffer from the disorder. This would put the number of people in the US with DI at roughly 89,400.
Reports of DI go back to 1894 when a Parisian dermatologist called Georges Thibierge documented cases of patients falsely believing they had scabies. However, symptoms and causes vary wildly. Bugs are a common culprit. Patients often complain of "crawling" and "biting" sensations. They might also claim pathogens are leaving marks on their skin or building nests.
More recently, there has been Morgellons disease, which was first identified in 2001. Sufferers are convinced there are fibers embedded in their skin, left there by mysterious – possibly alien – creatures that live in the body.
Singer-songwriter Joni Mitchell described it as "this weird incurable disease that seems like it's from outer space... Fibers in a variety of colors protrude out of my skin: they cannot be forensically identified as animal, vegetable or mineral. Morgellons is a slow, unpredictable killer – a terrorist disease. It will blow up one of your organs, leaving you in bed for a year."
But a two-year, half-a-million dollar study led by the CDC found nothing. Doctors say it isn't real.