The Ross-Mcdonald model revisited: linking transmission and within-host dynamics

We present a model that explicitly links the epidemiological Ross-Macdonald model with a simple immunological model through a virus inoculation term that depends on the abundance of infected mosquitoes. We explore the relationship between the reproductive numbers at the population (between-host) and individual level (within-host), in particular the role a certain measure of infectivity (defined in terms of the number of target cells infected) and viral clearance rate play in the coupled dynamics. The conditions for a disease outbreak require, for the average individual in the population, to have an active (within-host) viral infection. This infection depends on the viral load and the proportion of infected cells which are quantities that change in time. Only when these two quantities are sufficiently large, the epidemic outbreak may occur. We also describe a particular kind of transmission-clearance trade off for vector-host systems with a simple structure.