An analysis of the spread of several species of disease-carrying ticks included this depressing finding: the bacteria that causes the disease anaplasmosis in mammals when ticks bite them also helps the ticks survive extreme cold snaps. It’s like a nastiness two-fer:
Cold hardiness in these ticks is also enhanced by the presence of so-called antifreeze proteins, namely I. scapularis antifreeze glycoproteins (AFGP). These proteins are typically large glycoproteins that bind ice crystals. Remarkably, infection with Anaplasma phagocytophilum enhances expression of IAFGP, so that A. phagocytophilum-infected ticks are more likely to survive freezing episodes than uninfected ticks.
The whole paper, which goes into great detail about the reasons for ticks’ range expansion, is here.