Emerging infectious diseases in a globalized world

The impact that zoonoses have today worldwide on human populations is an unprecedented phenomenon. Three quarters of emerging infectious diseases that affect people have its origin in animals. This paper analyzes the conditions are necessary for an epidemic to occur: the species leap, the amplification, and the propagation. Currently, the natural systems are changing at an unprecedented rate and can modify the interactions between humans and reservoirs and vectors of viruses. Most of these changes have an anthropic origin and can increase the probability of species leap. One of the most important environmental changes taking place is the deforestation in tropical regions, whether to create space for new human settlements, land for pasture, crops or farming, or for commercial logging. The demographic increase plays an important role from an epidemiological point of view because does that the urban areas grow in inhabitant numbers and facilitates the amplification of the infection. For this reason, cities are exposed to epidemics and we must prepare them and protect them against future epidemics. Current mobility is unprecedented in human history and represent a critical epidemiological factor that increases the risk of disease propagations. Much of the emergence, amplification and propagation of the zoonosis are consequence of human activity. In this sense, one of the things we must learn as quickly as possible is that we need to change our relationship with the natural systems, because our actions can have consequences - such as pandemics.