Emerging infections represent a concern especially when their increase is rapid and their mortality high. They can be caused by previously undetected or unknown pathogens, or by known agents affecting new geographic sites or new populations, or by re-emerging agents whose incidence of disease had significantly declined in the past. Main causes of emerging infectious disease spread include crowding, mobility (tourism, migration, asylum seekers, refugees), centralization of food production and supply and new food vehicles, war, famine and displacement, and change in vector distribution and susceptibility.Another important issue regarding emerging infectious diseases is the source of pathogens, that in 60.3% of cases is a non-human animal origin (zoonotic pathogens). If viral emerging infections represent a concern mainly in underdevelopped area of the world, the emergence of antimicrobial resistance is a growing concern worldwide but especially in developed and high income countries, where misuse and overuse of antibiotics among humans and in the veterinary setting, including animal feeding, artificially created the selection of resistant strains.
Future threats include not only diseases caused by viral agents, such is the case of Ebola virus disease periodical re-emergence, but also infections with antibiotic resistant bacteria: it is estimated that in 2050 deaths due antimicrobial resistant infections will overcome those by cancer.