Cross-scale dynamics and the evolutionary emergence of infectious diseases

Sebastian J. Schreiber; Ruian Ke; Claude Loverdo; Miran Park; Priyanna Ahsan; James O. Lloyd-Smith

Consistent with theoretical expectations, a non-zero probability of evolutionary emergence requires the mutant's reproductive number R m to be greater than one (Fig 2) . However, the mixture of selective advantages or disadvantages of the mutant strain that give rise to R m > 1 depends in a complex manner on the pathogen's life history traits, such as the duration of the infection (Fig 2A,B vs. C,D) and the transmission bottleneck width (Fig 2A,C vs. B,D) . Notably, for long-term infections with a large transmission bottleneck size, the emergence probability can be effectively zero (i.e. < 10 −16 ) for mutant strains whose reproductive number exceeds one (white region bounded by the solid red curve in Fig 2D) -a finding not explained by classical theory. As we shall show, this outcome is predicted by a new quantity, the cross-scale reproductive number (α) of a mutant virion -the mean number of mutant virions transmitted to susceptible individuals All rights reserved. No reuse allowed without permission.