Emerging Infectious Diseases: an Ecological Look on the Invasion Process How speciation theories apply to emerging pathogens

Abstract

Emerging infectious disease pathogens have previously been classified into three categories: virulence jumpers, species jumpers and geographic invaders. A parallel is drawn with animal and plant speciation theory used to differentiate natural evolution in new geographic areas or new ecological niches; speciation in allopatry (vacariance or peripatry) or sympatry. In this exercise, the theoretical concepts above are illustrated with 7 viral diseases that have been emergent in the recent past: West Nile, chikungunya, bluetongue serotype 8, African swine fever, HIV-1, foot-and-mouth disease PanAsia and H5N1 highly pathogenic avian influenza clade 2.2. Schematically, species jumps undergo sympatric adjustment, where evolution takes place in distinct ecological niches in one geographic area. Virulence jumpers evolve in sympatric-like conditions, in a niche where the pathogen was already present but has gained a selective advantage. Peripatric adjustment refers to evolution of a pathogen after a geographic jump, in an area distant from its original distribution. Geographic jumpers are often vector-borne or very resistant to environmental destruction. Peripatric evolution is often limited to minor genetic changes required for adaptation to a new vector, for example. Sympatric evolution results in major genetic changes, due to adaptation to a novel host or different driving forces in different production systems. Genetic change in virulence jumpers is frequently restricted to the mutations conferring the increase in virulence jump itself. Sympatric and peripatric adjustment are the result of disease emergence in a different niche, whereas sympatric-like evolution in the case of a virulence jump is the cause of disease emergence. Anthropogenic forces act on numerous levels of the biological invasion process.