Host resistance and tolerance to vector-borne pathogens have contrasting effects on disease dynamics

Variation in host resistance and tolerance to pathogens can have important effects on pathogen evolution.  However, the effects of host defense mechanisms on disease spread are not well understood.  We hypothesize that tolerance and resistance will have contrasting effects on pathogen spread, mediated by vector preference for diseased or healthy hosts.

We developed a vectored SEI (Susceptible, Exposed, Infective) epidemiological model, with vector preference for either symptomatic or asymptomatic hosts.  Host tolerance to infection was varied by incorporating a Carrier state into the model (i.e. hosts that are infectious but show no symptoms).  Resistance was varied by modifying the rate at which Exposed hosts became either Infectives or Carriers.  We first compared disease dynamics in a single patch model. We then expanded this to a two patch system, to explore the potential for pathogen spillover from a resistant or tolerant patch into a neighboring susceptible patch.

Dynamics for the single-patch model showed that resistance reduced disease incidence, largely independent of vector preferences.  In contrast, a tolerant patch can act as a source of infectious vectors, especially when vectors preferred asymptomatic hosts. These conclusions were supported by results from the coupled patch system, which showed the greatest pathogen spillover into the susceptible patch when adjacent to a tolerant patch and with vector discrimination against symptoms. These results suggest that understanding the precise form and degree of host defense and vector preference may be important for disease management.