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SEI compartment model diagram illustrating age-specific density-dependent direct transmission with host demography (MD). Indirect transmission and fomite dynamics are indicated in grey (MDI). Transmission terms in brackets are replaced with (β′aa Sa Ia + β′ja Sa Ij)/N and (β′jj Sj Ij + β′aj Sj Ia)/N for frequency-dependent models (MF and MFI) (table 1 provides parameter definitions).
