Ecological specialization in vectors alters transmission thresholds and endemic dynamics in multi-host, multi-vector systems.

Modeling vector-borne pathogens that circulate among several host and vector species hinges on how the force of infection (FOI) is defined. In an i-host, j-vector susceptible-infectious-recovered modeling framework I compare two common FOI denominators: (i) a weighted form in which vectors bite preferred hosts disproportionately, and (ii) an unweighted form that assumes opportunistic biting. Using identical parameter sets calibrated to primate-Aedes data from Kédougou (Senegal), the weighted FOI doubles the basic reproduction number (R0) relative to the opportunistic FOI and can shift R0 across the epidemic threshold. It also produces higher long-run prevalence and larger oscillations. Both autonomous formulations undergo a forward transcritical bifurcation at R0 = 1. Selecting an ecologically realistic biting assumption is therefore critical for predicting sylvatic-to-urban spillover risk and designing interventions in multi-host systems.