Infectious diseases still cause vast damage worldwide. As well as
known threats, we face the ever-present risk of a new pandemic, and
the rising emergence of drug-resistant infections. However, as our
knowledge of contagion has improved, infectious diseases have on
the whole declined. The global death rate for such diseases has
halved in the past two decades.[35]
As infectious diseases wane, attention is gradually shifting to
other threats, many of which can also be contagious. In 1950,
tuberculosis was the leading cause of death for a British man in his
thirties. Since the 1980s, it has been suicide.[36] In recent years,
young adults in Chicago have been most likely to die from homi cide.
[37] Then there are the wider social burdens of contagion. When I
analysed neknomination back in 2014, online transmission seemed
like a tangential issue, almost a curiosity. Three years later, it was
dominating front pages, with concerns about the spread of false
information – and the role of social media – leading to multiple
government investigations.[38]
As our awareness of contagion increases, many of the ideas
honed in the study of infectious diseases are now translating to other
types of outbreaks. After the 2008 financial crisis, central banks
latched onto the idea that the structure of a network could amplify
contagion, a theory pioneered by STI researchers in the 1980s and
1990s. Recent efforts to treat violence as an infection – rather than
simply a result of ‘bad people’ – echo the rejection of diseases
caused by ‘bad air’ in the 1880s and 1890s. Concepts like the
reproduction number are helping researchers quantify the spread of
innovations and online content, while methods used to study
pathogen sequences are revealing the transmission and evolution of
culture. Along the way, we’re finding new ways to speed up
beneficial ideas and slow down harmful ones. Just as Ronald Ross
hoped in 1916, a modern ‘theory of happenings’ is now helping us
analyse everything from diseases and social behaviour to politics
and economics.
In many cases, this has meant overturning popular notions of how
outbreaks work. Like the idea that we need to remove every last