The decline of infectious diseases in the developed world
Infection used to be a leading cause of death. One hundred and fifty years ago, infectious diseases caused over a third of all deaths in England. Almost without exception, all have declined dramatically in importance since then, as illustrated in the following graph.
Measles, whooping cough, diphtheria and scarlet fever were, at the dawn of the 20th century, four of the biggest killers of children in the UK. Deaths from all four fell in a similarly impressive fashion during the first half of the century, before the availability of either vaccination or antibiotics, as depicted in the accompanying chart. There has never been a vaccination against scarlet fever.
Immunisation played only a very limited role in the decline in mortality from infectious diseases during the twentieth century.[1]
What goes up must come down – the natural cycle of infectious diseases
Diphtheria rose from being a little heard of disease in the mid 19th century to becoming a major killer by the beginning of the 20th century. This is an example of the natural waxing and waning of infectious diseases. Bubonic plague killed 25 million Europeans (a third of Europe’s population) in five devastating years during the 14th century; yet this disappeared without any medical intervention. Today’s ‘plague’ is AIDS. This disease, unheard of only a generation ago, is now predicted to kill more people than the plague: over half a million children died from AIDS worldwide in 2005. Smallpox grew from a relatively mild illness in the sixteenth century to become a serious threat. Polio is another disease that changed from being comparatively harmless to a dreaded disease over the course of a few decades. What is remarkable is that most of these changes happened naturally, unrelated to any medical intervention. This serves as a reminder that, whilst the decline in the seriousness of a disease may be the result of a medical advance, it may also happen quite independently.
[1] McKeown T, Record RG, Turner RD. An Interpretation of the Decline of Mortality in England and Wales during the Twentieth Century. Population Studies 1975; 29(3): 391-422.
