fever fog

plural fever fogs

1. Any mist rising from swampy ground, formerly believed to cause fever; a miasma.

   Miles on miles of quagmire, varied only by bright green strips of comparatively solid ground, and by deep and sullen pools fringed with tall rushes, in which the bitterns boomed and the frogs croaked incessantly: miles on miles of it without a break, unless the fever fog can be called a break.

   1886 October – 1887 January, H[enry] Rider Haggard, She: A History of Adventure, London: Longmans, Green, and Co., published 1887, →OCLC