Modeling the Spread of Crimean Congo Hemorrhagic Fever with Tick Co-feeding

Crimean Congo hemorrhagic fever (CCHF) is a viral disease in animals and humans. Ticks transmit the virus that causes this disease to susceptible hosts by feeding on them, and ticks can acquire the virus by feeding on an infected host. The tick species most commonly associated with CCHF feed on different hosts at different stages in their life cycle: larvae and nymphs feed on small mammals, while adults feed on large mammals, like humans and cattle. An additional transmission pathway, co-feeding, occurs when infected and susceptible ticks feed in close proximity on the same host, allowing viral transmission between ticks even if the host remains uninfected. In this work, we developed the first system of ordinary differential equations capturing CCHF transmission that includes co-feeding dynamics, seasonal variation in tick populations, and all three feeding life stages of ticks with their subsequent hosts. We adapted the model to Uganda's Cattle Corridor, a region with frequent human-cattle interactions and reported CCHF activity. Simulations explored both baseline and immigration event scenarios, capturing realistic ecological and epidemiological dynamics. By varying the co-feeding transmission, we found notable effects on the hosts and ticks, including a shift in timing of seasonal infection peaks and changes to the number of human infections from ticks or cattle. The inclusion of additional tick life stages demonstrates how co-feeding strengthens viral circulation within ticks and increases host infectivity. These results highlight the importance of including ecological complexity in models of CCHF transmission and to illustrate the effects of co-feeding.