Urban sprawl behind growth in dengue fever

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The move from the countryside to big cities such as Sao Paulo has led to a rise in dengue fever – AFP

The world’s sprawling megacities are providing perfect breeding grounds for the mosquito that spreads dengue fever, experts have warned, as new figures show that the number of deaths from the disease has risen dramatically.

According to the Global Burden of Disease study, published by the Lancet, the number of deaths from the tropical disease increased by two thirds from 24,500 to 40,500 between 2007 and 2017.

While deaths are still relatively rare compared to the number of cases – there were 104.8m cases of dengue in 2017 – the authors of the study point out that dengue is one of the few infectious diseases which is on the rise – the number of cases is thought to have nearly doubled in the last five years.

Dengue – also known as break-bone fever because of the severe joint pain it causes – is spread by the Aedes aegypti mosquito and 40 per cent of the world’s population live in areas where there is a risk of contracting the disease.

Dengue mainly occurs in densely-packed urban areas, particularly where there are pools of standing water which act as breeding grounds for the mosquito.

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Dr Bobby Reiner, one of the authors of the study and assistant professor at the University of Washington, said the reason for the increase in the disease was because of the widespread shift from rural to urban living. Those living in poor conditions in the world’s “unplanned megacities” are particularly at risk.

“Dengue is an urban mosquito-borne disease. There’s a growing population of people living in poor urban areas where there are no screens on windows, no air conditioning and where there is a lot of standing water. These are ideal conditions for mosquitoes,” he said.

Dr Reiner said there were few proven interventions to combat the disease – the only vaccine against dengue is imperfect and there has been little research on control measures, such as insecticides.

“There is a lack of evidence about what to do about it,” he said.

There are four different dengue serotypes – or strains – and a person who has been infected with one serotype is more likely to develop the severe form of the disease if they are infected again with a different one.

Dr Rachel Lowe, assistant professor at the London School of Hygiene and Tropical Medicine, who was not involved in the study, said people were moving around the world in large numbers, therefore increasing their chances of being exposed to different serotypes.

She added: “More frequent interaction between the different serotypes could result in more people developing severe dengue, which in some cases can be fatal.

“When you have these sprawling urban areas, where there is poor sanitation and close contact between the vector and human there is bound to be a rise in the number of cases.”

The dengue mosquito bites during the day so malaria control efforts such as bed nets do not work, she added.

“It’s extremely difficult to control the vector and once it’s established it’s very difficult to get rid of it. Things like improved sanitation and infrastructure is key in making sure people have proper running water so they don’t rely on temporary water storage containers,” said Dr Lowe.

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