The unfold of city-loving malaria mosquitoes may pose a critical risk to Africa, in keeping with science


A man sleeps in a mosquito net in Somalia.

Feisal Omar / Reuters

By Mohammed El-Said September 15, 2020, 11:55 am

An Asian malaria-carrying mosquito that has adapted to urban life can spread to dozens of cities on the African continent, according to a new model study. This could put more than 100 million additional people at risk for the deadly disease, including many who have never been exposed to the disease before and lack immunity.

The mosquito species Anopheles stephensi poses a serious new threat to African cities, says Francesca Frentiu, a geneticist at the Queensland University of Technology who was not involved in the research. She praises the work as “an important effort that is underpinned by robust methods”.

Malaria, which kills more than 400,000 people each year – most of them African children – is caused by Plasmodium parasites and is spread by several species of mosquitoes. In Africa, A. gambiae is the main one that thrives in rural areas. Recently, however, scientists have also discovered A. stephensi, which adapts well to city life and has long been spreading malaria in urban settings in Asia. A. stephensi jumped from Asia to the Arabian Peninsula between 2000 and 2010 and then made another jump to the Horn of Africa; Scientists first discovered it in Djibouti in 2012, and later in Ethiopia and Sudan.

Janet Hemingway, an insect molecular biologist at the Liverpool School of Tropical Medicine, and colleagues used data on every location A. stephensi is known to be found – including variables such as average annual temperature and seasonality of rainfall and human population density – to create maps of the places in Africa where the mosquito might next settle.

The Anopheles stephensi mosquito

Sinclair Stammers / Science Source

The results are worrying. Of 68 African cities with populations over 1 million, 44 appear to be suitable habitats for A. stephensi, the team reports in the Proceedings of the National Academy of Sciences this week. Together in these cities – from Casablanca (Morocco) to Durban (South Africa) – 126 million people live, 20.5 million of them in the greater Cairo area and another 19 million in Lagos (Nigeria).

If A. stephensi continues his incursions, there is “a very real possibility of mass eruptions” that could be “catastrophic,” the researchers write. The fact that countries in North Africa are vulnerable is particularly worrying as they currently have very little or no malaria and the people there have no immunity.

The World Health Organization has warned Africa about A. stephensi and called for active monitoring of the mosquitoes. The results suggest cities across the continent should take these warnings to heart, says Marianne Sinka, a zoologist at Oxford University who led the research.

The maps the team created will be helpful in tracking and fighting malaria, says Tamar Carter, a biologist at Baylor University who was not involved in the study. However, Carter says more research is needed to determine just how great the threat posed by A. stephensi to African cities – and how limited resources can best be used to combat it.

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