It's just an update of the miasma theory of the 19th century. >The miasma theory is an obsolete medical theory that held that diseases—such as cholera, chlamydia, or the Black Death—were caused by a miasma, a noxious form of "bad air", also known as night air. The theory held that epidemics were caused by miasma, emanating from rotting organic matter. In the 19th century, France tried to build a canal across Panama but were defeated by "malaria" - which is French for "bad air". The hot humid air of Panama smelled of rotting vegetation so the French doctors thought it was unhealthy and caused malaria. It was later discovered that malaria is caused by a parasite spread by mosquitos.