Co-feeding transmission leads to bi-stability of tick-borne disease spread dynamics

Considering that co-feeding transmission depends on the loads of infected ticks on each host, we develop a tick-borne disease dynamics model with co-feeding transmission probability peaking at an intermediate level of infected tick loads. We stratify tick and host population by their infection status and divide the vector population in terms of infection status and post-egg stages (larvae, nymphs and adults). We use the tick population dynamics and disease spread basic reproduction numbers and co-feeding transmission characteristics to describe the disease endemic structure, and show, for the first time, that density-dependent co-feeding transmission provides a novel mechanism for bi-stability. Numerical simulations based on parameters from laboratory and fields data confirm the possibility of bi-stability in biologically realistic settings, and sensitivity analyses show that the nymphal tick load value at which the co-feeding transmission probability reaches the maximum impacts most significantly on the stable endemic equilibrium value.