Being an MD, I was flabbergasted when two of my colonists came down with malaria on the same day: Decembary 3, after a severe cold snap in autumn and several nights of sub-freezing temperatures since then. Malaria is mosquito-borne and those critters do not do well during wintry conditions. OK, it's a fantasy game, but let's not get TOO fantastic with a well-understood condition like malaria. There's enough ignorance about infections circulating already!
Ok, you say the bug is that you got Malaria in a cold biome and want Plaque instead ?
I'll review this, but keep in mind space mosquitos could possibly survive in cold climates. Thank you for the feature request.