regional environmental transformations, and of their synergy with the ecological and evolutionary consequences of inadequate or inappropriate policies or methods of vector control and disease prevention, have unwittingly promoted disease emergence. The 'ecological' changes taking place as a result of public health agencies' actions (or inaction) involve pathogen biology and are small scale in time and space: selection for vector pesticide and antimicrobial resistance. However, the cumulative effect of micro-scale processes involving pathogen adaptation and host range expansion (or re-expanding) can ultimately produce regional and even global consequences. However, policy action and inaction outside the domain of biomedical or public health agencies has produced ecological changes at a historically unprecedented rate and scale. Urbanization, agricultural and food production intensification, alteration of natural habitat, along with concomitant loss of ecosystem functions, have transformed entire regional ecosystems during the past 50 years. The role of urbanization cannot be underestimated. The direct land use changes associated with urbanization effectively concentrate human, animal reservoir and vector populations at unprecedented densities. But urbanization also is strongly tied to socio-economic and cultural factors, along with human migration dynamics, affecting agricultural and food production intensification, as well as rural and natural ecosystems. In the case of food production and distribution, dramatically increased contact with and transport of wildlife (e.g., bush meat trade in Africa), and increased ruralurban transport and concentration of wild species for the exotic food market (e.g., civet cats in Guangdong, China), is another contributor to increasing disease emergence. It can be assumed these impacts on wildlife populations also contribute to changes in the composition of ecological communities on a regional scale (52) , and often result in a hyper-abundance of small mammal species low in the food chain, which are likely to serve as human disease reservoirs. Similar effects of ecological disruption appear to generally apply to invertebrate commu- Whether a disease 'jumps' to the regional population and the global human population scale is determined by quite different processes. These depend on demographic and transport patterns related to processes, like urbanization, influencing pathogen transmission and behavior operating on the regional and global scales. Physical environmental processes such as climate variability (on the right side of the figure), which are episodic by nature, include short term and small scale variations in the form of seasonal storms (e.g., monsoons), for example, as well as larger time and space scale variations. These include, for example, decadal and regional scale changes in weather patterns such as El Niño. These climate changes and weather events can precipitate floods and droughts. These act as cross-scale mediators that directly affect disease reservoir and vector populations, or pathogens (e.g, dispersal via flood waters). They cause the disease to jump from a smaller demographic unit to a larger one (e.g., from a single village to a district). Human Factors such as land use and land cover changes (Table 1 and Fig. 1 ) produce ecosystem changes contributing or magnifying the cross-scale processes. For example, urbanization and deforestation increase the magnitude of floods and droughts resulting from natural or anthropogenic climate variation. nities (53) , the kinds of organisms most commonly serving as human disease vectors. The estimated acceleration of natural species extinction rates by orders of magnitude over nonanthropogenic extinction rates (54) gives an indication of the scale and magnitude of change in natural communities, particularly in the tropics. In these regional ecosystems, the original extent of tropical forest has declined to a fraction of its original area with concomitant affects on biodiversity (38) .