There have been competing and conflicting ideas about diseases in different phases of human civilization, and none of them is said to be exclusively deterministic and universally acceptable. Disease has been defined in a way society wanted it to be defined, and consequently, the concept and ideas of illness are found to be changing with the changes of time and culture. More importantly, an interpretative rather than positivist approach to determining the definition of disease or illness has also been given by historians, sociologists, and anthropologists. This book is not intended to revisit this area and re-examine it. Broadly speaking, disease may be, in the light of modern medical research, due to several groups of causes, and specific aetiology for a specific disease has been established after the discovery of germ theory. It may be due to congenital defects or faulty working of the organs or may be the result of improper nutrition. There are certain diseases caused by some microbes (viruses, bacteria, or parasites), which are communicable from one person to another. This is the most important category of diseases from the point of view of public health services because these diseases can be prevented, and many can be successfully treated. Many such diseases, which caused havoc in colonial India, still pose a serious threat to the state and the people.

The most panic-inducing disease in British India was fever, which, in one form or another, had taken millions of lives. Besides mortality, fever also caused thousands of cases of illness, leaving the affected people weak, listless, and wrecked. British India experienced various types of fever, such as Burdwan fever, Dumdum fever, malarial fever, and so on—black fever, known as kala-azar (visceral leishmaniasis), being one of the most dangerous among them. Kala-azar was widely prevalent in colonial eastern India but was not only an Indian disease. It was rather a widespread disease and occurred in many parts of the world during the period under study, exhibiting its presence in China, Arabia, Sudan, Central Africa, Tunis, Sicily, Italy, Algeria, Crete, Spain, Portugal, Greece, Malta, Turkestan, Central and South America, South Africa, and so on.