Invasive Asian mosquito species threaten African cities

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A mosquito species originally from Asia threatens to expose tens of millions of urban residents in Africa to a higher risk of malaria as the invading insect spreads across the continent, according to a study on Monday.

Malaria – which killed 400,000 people in 2018, mainly children in Africa – is caused by parasites that spread around 40 species of mosquitoes among people when they are fed.

The Anopheles gambiae group of mosquito species is the main driver of the spread of malaria in Africa, but these insects do not like the polluted puddles in cities and have not learned to place their larvae in urban freshwater tanks.

For these reasons, malaria transmission in Africa occurs mainly in rural areas.

In a new study published in the Proceedings on the National Academy of Sciences (PNAS), medical entomologist Marianne Sinka of Oxford University recorded the spread of another species, Anopheles stephensi, that originated in Asia.

This species has learned to slide through cracks to gain access to water tanks, and prefers those made of brick and cement.

“It’s the only thing that’s really good at getting into central urban areas,” Sinka told AFP.

Anopheles stephensi caused a major outbreak in the city of Djibouti in the Horn of Africa, a city free from malaria, in 2012 and has since been seen in Ethiopia, Sudan and elsewhere.

Sinka and colleagues combined location data for the species with spatial models that identified the environmental conditions that characterize their preferred habitat: high-density urban areas where it is hot and it rains abundantly.

Their study found that 44 cities are “very suitable” for the insect and 126 million more Africans – mainly in the equatorial regions – are at risk of malaria compared to today.

“That means Africa, which is already the most exposed to malaria, could have an even bigger impact,” said Sinka, with 40 percent of the continent’s population in urban areas.

Unlike African mosquitoes, who like to bite people at night when it’s cool, Anopheles stephensi can feed in the evening when it’s warmer, making bed nets less effective.

So installing mosquito nets on windows, soaking the walls in insecticide, and covering your body are better ways to protect yourself from this species.

In the long term, the most effective measure is to combat the larvae: remove stagnant water and close the water tanks tightly before they can penetrate. These methods have been shown to be effective in India, Sinka said.

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