Tropical Diseases
Authors: W F Bynum
Journal: BMJ (2007)

“Textbook knowledge” has a bad ring these days. Knowledge grows so quickly that textbooks are assumed to be purveyors of yesterday's news. A century ago, medicine was also changing rapidly, and yet two textbooks, each published in 1898, transformed the medical landscape. William Osler's Principles and Practice of Medicine elegantly brought the glad tidings of the new scientific medicine to students of medicine throughout the world. Patrick Manson's Tropical Diseases spearheaded a new medical specialty, at a time of global imperialism. 

Manson, a genial Scot with practical experience in China, Formosa, and Hong Kong, was then a tropical medicine consultant in London. He had demonstrated that filariasis is transmitted through mosquito bites. This clinical research alerted him to the importance of parasites in “tropical” diseases and to the role of insects in spreading them. His hopes of retiring in the 1890s to Scotland were scuppered by some unfortunate investments, so he set himself up in London, where he also gave lectures on tropical diseases. These lectures and the book that grew out of them were widely appreciated and reported, including by the BMJ. 

Before Manson, tropical diseases were generally assumed to be simply that: the diseases of warm climates. They were assumed to emerge from the confluence of heat, humidity, vegetation, and decay that characterised these areas. Manson reversed the flow of causality: environmental conditions played only an indirect role in the geographical distributions of diseases. The conditions did not cause disease, but they permitted the existence of unique disease causing organisms in tropical climates. What Manson called the “cosmopolitan” diseases of the old world—diseases such as plague and leprosy—were ubiquitous because the germs could be found everywhere. They had largely disappeared from Europe. 

In a sense, Tropical Diseases merely applied the germ theory to diseases of hot climates. Nevertheless, Manson argued, tropical medicine was not simply a branch of bacteriology. Rather, the range of tropical organisms dangerous to human beings included many other biological groups: worms of all kinds, protozoa, and plasmodia. Tropical medicine was thus really a branch of parasitology, and since many of the organisms had complicated extra corporeal developmental cycles, and complex means of spread, including via insects, special tools and modes of thought were required to understand the range of diseases found in the tropics. 

Tropical Diseases appeared at an opportune time. Manson's protege Ronald Ross had discovered the malaria parasite in mosquitoes the year before and demonstrated its role in transmitting the disease in birds. Schools of tropical medicine in Liverpool, London, and several European countries established the discipline firmly. Journals, societies, and international meetings gave identity to this branch of medical knowledge and practice. 

Like many successful textbook writers, Manson became something of a slave to his own brainchild. He oversaw a sixth ever expanding edition in 1917. One characteristic of a classic is that it stays available: the 21st edition of Manson's textbook was published in 2003.