Quantifying Resilience in Single-Host/Single-Virus Infections

Due to theoretical and practical applications in biomedical, environmental, and industrial microbiology, robust metrics for quantifying the virulence of pathogens is vital. For many virus–host systems, multiple virus strains propagate through host populations. Each strain may exhibit a different virulence level. Likewise, different hosts may manifest different levels of host resilience to infection by a given virus. Recent publications have assessed metrics for quantifying virulence (VR) from growth curve data. Regardless of the metric used, a feature that most methods have in common is focus on the exponential growth phase of virus–host interactions. Often ignored is mortality phase. Following a report introducing the Stacy–Ceballos Inhibition Index (ISC), a robust metric to quantify relative virulence (VR) between viruses, we have turned attention to quantifying relative resilience (RR) between hosts in single-virus/single-host (SVSH) experimental infections. Although resilience during viral infection impacts the entire host growth curve, RR has particular biological significance during the mortality phase. In this report, we argue that calculating RR using a modified ISC provides a robust metric for comparisons between SVSH infections. Wet lab data from fusellovirus infections in Sulfolobales, bacteriophage infections in Mycobacteriales, and simulated infected-host growth profiles form the basis for developing this metric, RR, for quantifying resilience.