Optimal Strategies for Virus Propagation

TL;DR

This paper uses a mathematical model to analyze how viruses optimize their infection strategies within hosts, focusing on the timing of different infection stages to maximize viral load while evading immune responses.

Contribution

It introduces a mathematical framework to understand the timing strategies of viruses during infection, highlighting the tradeoffs between viral load and immune response.

Findings

Longer non-productive phase increases peak viremia.

Tradeoff between viral buildup and immune response influences viral strategy.

Questions raised about whether viruses have evolved optimal infection timings.

Abstract

This paper explores a number of questions regarding optimal strategies evolved by viruses upon entry into a vertebrate host. The infected cell life cycle consists of a non-productively infected stage in which it is producing virions but not releasing them and of a productively infected stage in which it is just releasing virions. The study explores why the infected cell cycle should be so delineated, something which is akin to a classic bang-bang control or all-or-none principle. The times spent in each of these stages represent a viral strategy to optimize peak viral load. Increasing the time spent in the non-productively infected phase ({\tau}1) would lead to a concomitant increase in peak viremia. However increasing this time would also invite a more vigorous response from Cytotoxic T-Lymphocytes (CTLs). Simultaneously, if there is a vigorous antibody response, then we might expect {\tau}1 to be high, in order that the virus builds up its population and conversely if there is a weak antibody response, {\tau}1 might be small. These tradeoffs are explored using a mathematical model of virus propagation using Ordinary Differential Equations (ODEs). The study raises questions about whether common viruses have actually settled into an optimum, the role for reliability and whether experimental infections of hosts with non-endemic strains could help elicit answers about viral progression.