This excerpt from Grist’s field guide to tomorrow’s climate-driven diseases introduces you to some of the carriers that are growing in number and expanding into new parts of the U.S. as the environment changes. The viruses, bacteria, fungi, and parasites they spread can cause joint pain, skin lesions, long-term memory problems — even death. Some of these maladies have no treatment or cure, though experts emphasize that numerous preventative measures to limit infection exist.