Wolbachia-induced mortality as a mechanism to modulate pathogen transmission by vector arthropods

Insecticide resistance and absence of clinical cures or vaccines for many vector-borne diseases has stimulated interest in using genetically modified arthropod vectors for disease control. Current transgenic strategies focus on vector susceptibility to pathogen infection, which is an inefficient target for pathogen transmission interference. Manipulation of vector survival is theoretically more effective, resulting in larger reductions in the expected number of human infections. A hypothetical method to manipulate vector survival is to drive mortality-inducing Wolbachia into populations. For varying patterns and degrees of induced mortality, we outline the conditions under which virulent Wolbachia introductions into vector populations are expected to succeed and quantify the resultant reduction in pathogen transmission. The most critical component to the success of this strategy is the pattern of induced mortality. For operationally feasible introductions, induced mortality must be delayed until after vector reproduction begins. If this condition is not met, introduction thresholds become exceedingly high, ranging from approximately 40% to 90% of the total adult population. Delayed induced mortality patterns can reduce introduction thresholds to approximately 15-45% of the total adult population. Reduction in cytoplasmic incompatibility with male age has negligible effects on introduction success regardless of the induced mortality pattern. Under proper circumstances, symbiont-induced manipulation of vector survival can theoretically result in up to 100% reduction in pathogen transmission, depending on Wolbachia parameters, magnitude and pattern of induced mortality, and duration of pathogen incubation in the vector. Our results indicate that a broadening of the current paradigm for genetic manipulation of vectors to parameters other than arthropod vector competence is justified and will reveal new research possibilities for vector-borne disease control.