There are many good books that have been written on mathematical
epidemiology. This list is incomplete, but is growing.
Roy Anderson and Robert May. Infectious Diseases of Humans, Dynamics
and Control, Oxford 1991.
O. Diekmann and J. A. P. Heesterbeek. Mathematical Epidemiology of Infectious Diseases. Model Building, Analysis, and Interpretation, Wiley 2000. Comment: Buy this book!