We consider a general model that describes the spatial propagation of a disease. The space is subdivided in patches (regions, cities, ...). In each patch a SIS model with a general transmission law describes the dynamics of the disease. The complete system takes into account disease transmission, birth, death and travel between patches. We compute the basic reproduction ratio for the complete system and we study the evolution of the disease according to the values of this basic reproduction number. The proofs are based on some properties of strongly monotone systems.