Urban expansion at the periphery of cities, sometimes called extended urbanisation, is creating "new ecological niches" for the spread of infectious diseases, according to a study which sheds light on the governance needed to reduce future outbreak risk.
According to the scientists, including those from the University if Lincoln in the UK, this kind of expansion of cities is altering the spatial relationships which shape how millions of people live and interact with each other and with nature.
The review study, published in the journal Urban Studies, assessed how the global trend towards urbanisation has contributed to the rise in the total number of disease outbreaks per decade since the 1980s.
Rapid urbanisation, particularly in developing nations of Asia and Africa, is creating fluid relationships between urban and rural environments with populations drawn to new types of suburban settlements on the periphery of cities, the researchers said in a statement.
These settlements, the study said, might be in the shape of suburban neighbourhoods, informal self-built settlements, refugee camps, or communities of workers living near mines or factories.
According to the study, these suburban and 'peri-urban' areas are more likely than cities to be the source of new and re-emerging infectious diseases.
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The scientists believe that the populations living in these regions are particularly vulnerable to diseases that jump the animal-to-human boundary, as they bring populations of humans and livestock into contact with displaced wildlife in a manner that does not happen in cities.
The neighbourhoods in these areas are often densely populated, poorly planned, lacking health infrastructure and out of sight of government authorities, the researchers added.
They said these areas also serve as a conduit between city and countryside -- making municipal, regional, and even national boundaries effectively "porous".
Recent SARS and Ebola outbreaks are high profile examples of epidemics which originated in these new types of suburban hinterland before spreading into larger, established cities, the study noted.
This structural weak spot to infectious disease outbreaks has largely been overlooked in academic studies of the epidemiology of global urbanisation, the researchers said.
According to the scientists, there are three key dimensions to understanding the link between urbanisation and infectious disease risk -- the dynamics of population change, infrastructure, and governance.
They said further interdisciplinary research is needed in these fields -- especially as the world responds to the current COVID-19 pandemic which first emerged in Wuhan, China, in December.
The researchers cautioned that without improved understanding, public health policymakers locally, nationally and internationally will be ill-equipped to identify and mitigate the heightened risk of infectious disease outbreaks posed by suburban sprawl.
"Economic growth, changing labour markets and conflicts are driving urban expansion and migration from rural-to-urban in developing countries at unprecedented pace," said Creighton Connolly, an urban geographer from the School of Geography at the University of Lincoln and lead author of the study.
"Improved transport infrastructure has cut journey times between countryside, suburbs and cities from days to hours. However the infrastructure vital for good public health, like health clinics and clean water, often lags behind," Connolly added.
The scientists believe that governance, particularly the mechanics for responding rapidly to disease outbreaks, are also weaker in these fringe communities in the so-called 'urban shadow' compared to established towns and cities.
They said this could be because jurisdictional responsibilities are often blurred in these areas.
A better understanding of the changing spatial relationships between cities, suburbs and countryside, the factors that shape these changes, and effective ways to adapt to them, will be key to reducing the risk of future outbreaks of infectious diseases, the scientists noted in the study.
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