Epidemic

In epidemiology, an epidemic is defined as a disease that appears as new cases in a given human population, during a given period of time, at a rate that substantially exceeds “normal,” based on recent experience. However, the definition of epidemic can be subjective depending on what is “normal.” For example, a few cases for a very rare disease like rabies may be classified as an epidemic, while cases of a common disease, as the common cold, would not.

Epidemics can be categorized based on the size or the intensity of appearance of cases of a new disease. For example, an epidemic may be restricted to one locale (an outbreak), more general (an epidemic) or even global (pandemic). Also, when diseases occur at a constant but relatively high rate in the population, it is termed as endemic. An example of an endemic disease is malaria in some parts of Africa (for example, Liberia) in which a large portion of the population is expected to get malaria at some point in their lifetimes.

Epidemics can also be classified by their pattern of transmission. The disease can be transmitted by a vector, from person to person, or from a common source such as contaminated water.

Some of the famous examples of epidemics include the bubonic plague epidemic of Medieval Europe known as the Black Death, the Great Influenza Pandemic concurring with the end of World War I, [Page 597]and the current AIDS epidemic, which some also consider to be of pandemic proportions.

The Bubonic Plague, or Black Death, was a devastating pandemic, which first struck in China. This plague traveled to Europe by rat-infested Italian ships trading goods across the Mediterranean Sea. The plague reached England by the late 14th century and within 4 years (1347–51) it had killed over a million people, one-third of Europe's entire population. Including Middle Eastern lands, India, and China, the Black Death killed at least 75 million people, taking the form of the most dangerous pandemic ever to be known in the history of epidemics. In addition to its massive effect on mortality, the Black Death irrevocably changed Europe's social, economic and cultural structure. The deaths changed the size of the civilization, which further led to changes in trade, the church, art, and music. The disease was completely eradicated in Europe only at the beginning of the 19th century, but survives in other parts of the world (Central and Oriental Africa, Madagascar, and Asia).