Vector behavior and pathogen spread: Implications of host resistance versus tolerance

Background/Question/Methods   Ecological theory suggests that vector preference for infected versus uninfected hosts can impact dramatically disease incidence. However, little information exists on the extent to which host resistance or tolerance to pathogens mediates these effects. Resistance is defined as a relative lack of infection whereas tolerance equates to infection without symptoms. Distinguishing between resistance and tolerance may be important epidemiologically if these traits are uncorrelated. I documented the preference of three species of sharpshooter leafhoppers, which are vectors of the pathogenic bacterium Xylella fastidiosa to grapevines. Next, I used a vectored “SEICS” epidemiological model to simulate disease dynamics for this system over different levels of plant resistance or tolerance to infection.

Results/Conclusions   The three vectors showed similarly strong (6 to 8-fold) preference for residing on healthy instead of infected shoots in a field trial. Results from the model suggest that resistant hosts should generally reduce disease prevalence. However, tolerant non-resistant varietals may act as pathogen sources, because they weaken the potential for vector discrimination against symptoms to temper pathogen acquisition and spread. Thus, an understanding of whether mild disease stems from host resistance versus tolerance to infection may be important for disease management.