The three case studies selected for illustration here are all too familiar to many epidemiology or toxicology students. These are the nutritional disease pellagra, the teratogenic drug thalidomide, and the HIV infectious disease which often leads to AIDS.

Pellagra is a disease associated with niacin deficiency, characterized by a typical dermatitis, diarrhea, dementia, and commonly death. Thalidomide was formerly used therapeutically as a sedative hypnotic, such as for morning sickness. Today it is used to treat some types of leprosy and as a test drug for some HIV-positive patients. Its use for morning sickness was discontinued because the drug was seen to have caused major fetal morphological anomalities when taken during the first trimester of pregnancy. AIDS is an acronym for acquired immune deficiency syndrome. It is a medical condition in humans, in which their immune system suffers a progressive failure, leaving them susceptible to fatal opportunistic infections. This syndrome is caused by the human immunodeficiency virus (HIV).

There are numerous epidemiologic events in history. The above three case studies were selected because they represent not only epidemiologic events of different eras, but also a wide spectrum of use of toxicologic studies.