1. R. Albert, A.L. Barabási, Rev. Mod. Phys. 74, 47 (2002); J.F.F. Mendes, S.N. Dorogovtsev, Evolution of Networks: From Biological Nets to the Internet and the WWW (Oxford University Press, London, 2003)
2. C. Castillo-Chavez, B. Song, in Bioterrorism - Mathematical Modeling Applications in Homeland Security, edited by H.T. Banks, C. Castillo-Chavez (SIAM, Philadelphia, 2003), p. 155
3. N.T.J. Bailey, The Mathematical Theory of Infectious Disease, 2nd edn. (Griffin, London, 1975)
4. R.M. Anderson, R.M. May, Infectious Diseases of Humans (Oxford University Oxford, Oxford, 1991); J.D. Murray, Mathematical Biology (Springer, Berlin, 1993); V. Capasso, Mathematical Structures of Epidemic Systems (Springer, Berlin, 1993); Epidemic Models, edited by D. Mollison (Cambridge University Press, Cambridge, 1995)
5. See, for example, I.B. Schwartz, H.L. Smith, J. Math. Biol. 18, 233 (1983); A.L. Lloyd, R.M. May, J. Theor. Biol. 179, 1 (1996); M.J. Keeling, P. Rohani, B.T. Grenfell, Physica D 148, 317 (2001); M. Kamo, A. Sasaki, Physica D 165, 228 (2002); H.W. Hethcote, SIAM Rev. 42, 4999 (2000)