This work focuses on the development of a simulation strategy able to quantify risks of airborne virus contagion in many scenarios found in enclosed domains by using high-fidelity fluid dynamics simulation to predict the trajectories and distribution of virus-loaded respiratory droplets over long times. Large-Eddy simulation is used to predict the turbulent flow fields in a city bus for different operating conditions of the Air Conditioning system. The time-averaged velocity distributions and associated turbulent kinetic energy are shown to be drastically dependent on the studied operating conditions. Lagrangian tracking of respiratory droplets is then used over long times on statically converged Eulerian flow fields to investigate their turbulent dispersion depending on the emitter position in the bus. Importance of air conditioning conditions on respiratory droplet trajectories and concentration in the configuration is illustrated indicating that air treatment devices play a crucial role in the mitigation solution of airborne virus propagation.