The term "mysterious illness" refers to a medical condition that is difficult to diagnose and treat due to its unknown cause or symptoms. Full definition
Even when clones appear healthy at birth, they often develop mysterious illnesses later. (discovermagazine.com)
Since the first reports of mysterious illnesses in the early 1980s, HIV and AIDS have touched nearly every American in some way, and operated as an undeniable, though often unacknowledged, force in shaping politics, medicine, culture and society. (artaidsamericachicago.org)
by MSNBC Stumped by mysterious illnesses in at least 600 dogs in the U.S., federal health officials have turned to consumers for help investigating problems possibly tied to chicken jerky pet treats made in China. (tampabayvets.net)