Figure 2
From: Contrasting within- and between-host immune selection shapes Neisseria Opa repertoires
Overview of the model.
(a) Schematic diagram of strains included in the model. Each isolate has two opa loci, each with two hypervariable regions (HV1 and HV2). One of two possible alleles can be expressed at each Opa locus (a or b at HV1; x or y at HV2). It is assumed there are no dose-response effects; i.e. a strain with the genotype bxbx is considered identical to bx. (Diagram modified from Callaghan et al.34). All possible strains can be selected for in the model (i.e. strains do not become extinct, they simply fall to extremely low frequencies), to account for the possibility of recombination between strains. (b) The model assumes that strains are inhibited from infecting hosts co-infected with or immune to strains sharing antigenic determinants by the parameter γ (where γ = 1 confers complete cross-immunity). (c) Deterministic equations used in the model. zi and yi represent the proportion of the host population immune to and infected with strain i respectively; wi represents the proportion immune to any strain; σ confers the rate of loss of infectiousness of a strain; β represents a strain's transmissibility; ε confers the rate of loss of immunity; and μ confers the average host death rate. The force of infection (λ) of any strain is determined by the product of its transmissibility and its total prevalence in the infected population (i.e. λi = β*Yi).
