As people remake the world's landscapes, cutting forests, draining wetlands, building roads and dams, and pushing the margins of cities ever outward, infectious diseases are gaining new toeholds, cropping up in new places and new hosts, and posing an ever-increasing risk to human and animal health. "Evidence is mounting that deforestation and ecosystem changes have implications for the distribution of many other microorganisms, and the health of human, domestic animal and wildlife populations," according to a report compiled by the Working Group on Land Use Change and Disease Emergence, an international group of infectious disease and environmental health experts.