Competition-colonization trade-off promotes coexistence of low-virulence viral strains

TL;DR

This study models how a competition-colonization trade-off among viral strains can lead to the coexistence of low-virulence variants, challenging the idea that virulence always increases during evolution.

Contribution

It introduces a mathematical model incorporating a trade-off between virulence and colonization success, explaining viral diversity and coexistence of low-virulence strains.

Findings

Biphasic dynamics with initial dominance of virulent strains

Existence of a steady state with low-virulence variants coexisting

Attenuation of virulence in the absence of immune response

Abstract

RNA viruses exist as genetically diverse populations displaying different phenotypes, including diverse degrees of virulence. The evolution of virulence in viral populations is, however, poorly understood. Based on the experimental observation of an RNA virus clone in cell culture diversifying into two subpopulations of different virulence, we study the dynamics of heterogeneous virus populations and the evolution of virulence. We introduce a competition-colonization trade-off into standard mathematical models of intra-host viral infection. Colonizers are fast spreading, virulent strains, whereas competitors are less virulent variants that are more successful within coinfected cells. We observe biphasic dynamics of the population: Early in the infection the population is dominated by colonizers, which later will be outcompeted by competitors. The simulations suggest the existence of a steady state where few low-virulence variants coexist. This equilibrium implies collective virulence attenuation in the population, in contrast to previous models predicting development of the population towards increased virulence. Nevertheless, the attenuation effect disappears if we include a highly simplified immune response in our models. Thus, the competition-colonization trade-off indicates a role for virulence in the modulation of the viral population diversity. The evolution of virulence is a dynamic feature of the population shaped by interactions between individuals and by the structure of the patchy habitat.