Emergence of new human pathogens are often associated with rural areas, where people have frequent contact with animal reservoirs of so as to invite infections. Cities, in contrast, are often the reservoirs, or core areas, for many established human pathogens. Cities can provide more robust chains of transmission. Both because of increased contact rates and because of the greater supply of susceptible individuals. Cities are essential arenas for both the evolution and ecology of human infections. It is believed that many important pathogens only established in humans following the neolithic revolution around 10,000 years ago, when early humans made the first settlements, that eventually grew into early cities some three to 5,000 years ago. This includes species jumps by smallpox, tuberculosis, measles, whooping cough and probably most other acute immunization infections that would rapidly fired out in the spars pre-settlement human populations. Transmission in cities was particularly be rampant in the beginning of the industrial revolution during the early part of the 19th century. Workers often lived in very crowded unsanitary conditions, in which contagent of tuberculosis, typhoid and cholera was rampened. Tuberculosis alone causing up to 25% of all deaths In many cities. In early industrialized cities like Liverpool and Manchester, the death rate from TB was ten times that of the surrounding rural areas. The death rate from childhood infections, like measles and whooping cough, we four times higher. Mortality rates on the whole were 50% higher than the national average. Sanitation, vaccination, and urban health infrastructure have greatly altered the abysmal situation of the past. However, big cities still play an important role in the dynamics of many infections Most epidemics of immunizing infections, for example, quickly burn out in smaller towns or villages because they run out of susceptible individuals to sustain the chain of transmission. Such infections can only persist in communities above a certain size. Or really, in communities in which the birth rate of un-vaccinated children is sufficiently high. Dynamically speaking, this leads to what is called island-mainland metapopulation dynamics. In ecology, a metapopulation is a group of local populations or communities connected by infrequent movement amongst them. In island-mainland epidemics, the pathogen retreats to a few big, cool cities during inter-epidemic periods, allowing the susceptible populations to build up in smaller communities. Intermittently, when susceptibles are numerous enough, For the effective reproductive number to exceed one, the pathogen can spread through smaller communities to cause broad-scale epidemics. This type of dynamic is clearly illustrated by pre-vaccination measles. In interepidemic periods, measles was only present in less than ten big cities. During the major epidemic that happened every two years or so, measles was present virtually everywhere. The spread out of the big cities happens in a very characteristic hierarchical fashion, where, on average, the timing of epidemic happens in an order of descending size and increasing isolation. This timing comes about because of key characteristics of human mobility, by which movement is more frequent between big cities and more frequent between communities close together. We see similar patterns of what is called hierarchical diffusion in many other childhood infections as well as seasonal influenza. Well this type of spread is inherently random. We can predict a relative risk of outbreaks using the circle gravity models of human mobility. Today in many European countries vaccine cover is high enough that no cities are big enough for sustained transmission of measles. However in contrast to the Americas, where measles is eliminated. Measles persists regionally by jumping from city to city. Causing epidemics that quickly die out locally. In disease ecology, we call this metapopulation persistence, as opposed to the more conventional local persistence, that relies on unbroken chains of transmission in each host community. Rabies in raccoons and plague in prairie dogs are examples of animal diseases that only can persist at the metapopulation level. Since the movement of wild animals are simpler and do not rely on complicated human transportation networks. We often see spatial waves will spread of rabies and plague, that are reminiscent of forest fires.