Emerging infectious diseases arise by a range of distinct phenomena, such as the resurgence or upsurge of pre-existing endemic infections, the arrival of exotic microorganisms and the appearance of genetically new microorganisms. The evolutionary emergence of new human pathogens is driven by changes in the biological barriers that determine host-pathogen interactions and therefore the transmission competence of any new partnership. True evolutionary emergence is rare. Among emerging infectious diseases other than infection by drug-resistant bacteria, there is a high percentage of zoonoses. This review focuses on infectious diseases that have emerged recently in new areas, where selection may favour microbial genetic novelties. Among these, vector-borne pathogens are particularly common.
The arrival, establishment and spread of exotic diseases: patterns and predictions. Nature Rev Microbiol. 2010 8(5): 361-371 doi: 10.1038/nrmicro2336
The impact of human activities on the principles and processes governing the arrival, establishment and spread of exotic pathogens is illustrated by vector-borne diseases such as malaria, dengue, chikungunya, West Nile, bluetongue and Crimean-Congo haemorrhagic fevers. Competent vectors, which are commonly already present in the areas, provide opportunities for infection by exotic pathogens that are introduced by travel and trade. At the same time, the correct combination of environmental conditions (both abiotic and biotic) makes many far-flung parts of the world latently and predictably, but differentially, permissive to persistent transmission cycles. Socioeconomic factors and nutritional status determine human exposure to disease and resistance to infection, respectively, so that disease incidence can vary independently of biological cycles.