1a vaporous exhalation formerly believed to cause disease 
also a heavy vaporous emanation (see EMANATION sense 2) or atmospheremiasma of tobacco smoke
2an influence or atmosphere that tends to deplete or corrupt freed from the miasma of poverty— Sir Arthur Bryant the enervating miasma of fear— The Times Literary Supplement (London)alsoan atmosphere that obscures FOG
Miasma theory was the scientific explanation for disease prior to germ theory. Miasma means ‘pollution’ but is a holistic word both physical and metaphysical. Miasma could emanate from  swamps, night air, ships, dead bodies, ill-will and immorality. Prisons in particular were believed to generate a lot of Miasma due to the festering, forgotten people inside.