The transmission and persistence of tick-borne infections, such as Lyme disease and encephalitis, are strongly influenced by the densities and the structure of vector and host populations. Those factors are especially important for ticks that feed on distinct host species at immature and mature life stages. When the seasonality of tick life cycle causes asynchrony among life stages, transmission of pathogens may be restricted in a short time period in which the life stages can overlap. The potential mechanisms that allow pathogen persistence in such populations are not yet well understood. Previous studies examined the importance of factors including the efficiency of transmission from hosts to ticks, the period of host infectivity, and co-feeding of ticks on the same host individuals. In this project, we investigated how tick and host densities, aggregation, and frequency of inter-ovarial transmission (i.e., mother to eggs) might affect the probability of pathogen persistence. To this end, we developed a difference equation model and analyzed the behavior of the system under multiple scenarios. Then, we extended the model to examine the effects of spatial distributions of hosts and ticks on a landscape.
Results/Conclusions
The results suggest that a low frequency of inter-ovarial transmission can be sufficient for pathogen persistence without invoking unrealistically long host infectivity. Because of asynchrony between larvae and nymph stages and the use of different host species by adults, transmission within life stages via co-feeding can have large influences on pathogen dynamics. We conclude that spatial and temporal aggregation of ticks is crucial for pathogen persistence by co-feeding that can result in successful pathogen transmission.
