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An unprecedented alliance of urban planners, doctors and scientists is needed to better prepare for "the looming threat of explosive urban epidemics" in an increasingly urbanised world, according to a review paper in The Lancet Infectious Diseases.

The world's urban population will double by 2050 and most of this increase will be in developing countries, according to UN estimates.

But how this will affect infectious diseases is poorly understood. Better research, surveillance, urban planning and policy are needed to keep new epidemics in check, says the paper published yesterday (2 February).

Rapid urbanisation is resulting in the decline of some diseases: better sanitation and public health programmes have reduced the spread of hepatitis A, while water and air pollution limit some disease vectors such as mosquitoes and sand flies in African cities.

But other vectors and pathogens have adapted to, or emerged in, growing cities. "Cities become incubators where all the conditions are met for outbreaks to occur," says the paper.

The migration of people to cities brings new diseases such as Chagas disease and leishmaniasis, traditionally rural diseases that are now increasingly common in cities — particularly in Latin America.

But the risk of disease varies within a city, depending on the infrastructure and wealth of neighbourhoods.

"Urbanisation is completely non-homogenous," Louis Loutan, one of the paper's authors and a  researcher at the University Hospital of Geneva, Switzerland, told SciDev.Net. "In a city there will be pockets where there is a comparatively higher risk of infectious disease."

Millions of people live in slums with no access to clean water and regular rubbish disposal. They "build their own dwellings from flimsy, scrounged materials and with no concern for vector hygiene," the paper says.

And high population density in cities means there is a "looming threat of explosive urban [disease] epidemics", including Ebola, chikungunya, yellow fever and dengue, according to the paper. "Urban epidemics can reach unprecedented scales and quickly become uncontrollable," especially in African cities where disease surveillance is weak.

"We need new tools for reporting and doing surveillance," said Loutan. "Mobile technology in cities is going to change reporting, access to information and mapping the distribution of the diseases to identify at-risk areas."

"Physicians in urban environments … need to be aware of the changes in infectious diseases associated with urbanisation," he added.

Delia Boccia, a researcher at the London School of Hygiene and Tropical Medicine, United Kingdom, told SciDev.Net: "Advances in biomechanical tools, such as vaccines and drugs, make an impact on preventing the spread of infectious diseases, but it is very clear now that urban health needs partnerships between public health and urban planning."

Link to full article in The Lancet Infectious Diseases

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The Lancet Infectious Diseases doi: 10.1016/S1473-3099(10)70223-1 (2011)