Epidemic Models and the Dynamics of Infectious Diseases

The study of epidemics has a long history with a vast variety of models and explanations for the spread and cause of epidemic outbreaks. Even today they are often attributed to evil spirits or displeased gods. AIDS (acquired immunodeficiency syndrome), the epidemic of the 1980’s and probably of the 20th century, has been ascribed by many as a punishment sent by God. Hippocrates (459–377 BC), in his essay on ‘Airs, Waters and Localities’ wrote that one’s temperament, personal habits and environment were important factors — not unreasonable even today. Somewhat less relevant, but not without its moments of humour, is Alexander Howe’s (1865) book in which he sets out his ‘Laws of Pestilence’ in 31 propositions of which the following, proposition 2, is typical: ‘The length of the interval between successive periodic visitations corresponds with the period of a single revolution of the lunar node, and a double revolution of the lunar apse time’.