Schematic diagram of within-host viral copy number (<i>V</i>) and immune currency (<i>I</i>) dynamics.

<p>The bold lines represent dynamical processes captured explicitly in equations S4, S5. In this model, the viral population dynamics are governed by two antagonistic processes, replication and control (by the immune system). The immune dynamics are in turn governed by three processes; maintenance (increasing immune stocks), stressors (depleting immune stocks) and a specific impact of virally-mediated immune modification (ranging from excitatory to suppressive). The dotted lines represent processes that are external to the model: 1) over-growth of the virus directly leads to increased bee mortality and collapse of the colony (<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1002735#ppat-1002735-g001" target="_blank">Figures 1</a> and <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1002735#ppat-1002735-g002" target="_blank">2</a>); 2) despite impending collapse within a focal colony, the virus can escape its host via horizontal transmission facilitated by its mite symbiont <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1002735#ppat.1002735-Rosenkranz1" target="_blank">[21]</a>, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1002735#ppat.1002735-Greatti1" target="_blank">[73]</a>; 3) the mite may gain further advantages from its association with an immuno-suppressive virus, as the suppression will further release immunological control of mite feeding; 4) the mite can affect honeybee survival <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1002735#ppat.1002735-Rosenkranz1" target="_blank">[21]</a>.