Public health generally refers to a function of government in attempting to prevent disease among the subject population. In many ways, it is largely a modern concept, although it has its roots in antiquity. After all, a ruler had an interest in keeping his subjects alive in order to continue to be a ruler.
In order for public health policies and programs to develop, it was necessary for the government to gain some understanding of the causes of disease. Early on, it was recognized that dirty water and lack of proper waste disposal were implicated in spreading vector-borne diseases. By Roman times, it was well-understood that proper diversion of human waste was a necessary tenet of public health in urban areas.
During the Black Death period in Europe, it was believed that removing the bodies would prevent further spread of the disease. Unfortunately, this did little to stem the plague, which was spread by rodent-borne fleas. Burning areas of cities resulted in much greater benefit, since it removed the rodent infestations.
During the modern era, most governments well recognize the importance of public health programs in reducing the incidence of disease, disability, and the effects of aging. Public health programs which provided smallpox vaccination have in recent years successfully eradicated that disease from the face of the Earth. Certainly, one of the most important public health issues of the present is that of AIDS.