CITY dwellers in the tropics are increasingly under threat from malaria. Even though urban areas have traditionally been considered low-risk, researchers believe that urbanisation is turning malaria into a city problem too.
“Two years ago it wasn’t being discussed at all,” says Marcia Caldas de Castro of the Office of Population Research at Princeton University. “But it is going to get worse and worse.”
One problem is the rapid growth of urban populations, which are increasing by about 10 per cent a year in sub-Saharan Africa. Around one-third of the population in the region now live in cities. But by 2025 it could be around half.
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“This has a very dramatic effect on the epidemiology of disease,” says Jürg Utzinger of the Swiss Tropical Medicine Institute in Basle. “It is a completely different beast to tackle.”
There used to be very few places for mosquitoes to breed in an urban setting, says Caldas. But that is no longer true. As urban areas sprawl outwards, people dig holes for bricks, which fill with water. What’s more, urbanites have a lower resistance to malaria than rural populations.
But although urban malaria presents new problems, it may also be containable. Utzinger and his co-authors reviewed research on urban malaria and conclude that tackling mosquito larvae will be more effective than in rural areas. Draining an urban water source will impact more people, for example, because city-dwellers live closer together (American Journal of Tropical Medicine and Hygiene, vol 71, supplement 2, p 118).
Draining breeding sites and killing larvae by introducing fish could be very effective, he says. But these approaches have not been popular for more than 50 years, as spraying with DDT became the catch-all strategy.
Caldas and her colleagues report the results of an eight-year project to control urban malaria in Dar es Salaam, Tanzania (supplement 2, p 103). They found that education and community efforts to reduce mosquito breeding sites as well as developing local medical services reduced malaria infections among children from 60 to 17 per cent.