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A man sleeps inside a mosquito net in Somalia.
Feisal Omar / Reuters
By Mohammed El-Said
An Asian malaria-carrying mosquito that has adapted to urban life has the potential to spread to dozens of cities across the African continent, a new modeling study suggests. That could put more than 100 million additional people at risk for the deadly disease, including many who have never been exposed before and do not have immunity.
The species of mosquito, Anopheles stephensi, poses a serious new threat to African cities, says Francesca Frentiu, a geneticist at Queensland University of Technology who was not involved in the research. She praises the work as “a major endeavor, backed by strong methods.”
Malaria, which kills more than 400,000 people per year, most of them African children, is caused by Plasmodium parasites and spread by various species of mosquitoes. In Africa, the most important is A. gambiae, which thrives in rural settings. But recently, scientists have also discovered A. stephensi, which is well adapted to city life and has long spread 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, then in Ethiopia and Sudan.
To measure its potential to spread further, Janet Hemingway, an insect molecular biologist at the Liverpool School of Tropical Medicine, and her colleagues used data from all the places where A. stephensi It is now known that it occurs – including variables such as mean annual temperature, rainfall seasonality, and human population density – to produce maps of where in Africa the mosquito might next establish itself.
the Anopheles stephensi mosquito
Sinclair Stammers / Scientific Source
The results are puzzling. Out of 68 African cities with a population of over 1 million, 44 appear suitable habitats for A. stephensithe team reports this week in the procedures of the National Academy of Sciences. Together, those cities, from Casablanca, Morocco to Durban, South Africa, are home to 126 million people, including 20.5 million in the Cairo metropolitan area alone and another 19 million in Lagos, Nigeria.
Yes A. stephensi continues its forays, there is “a very real possibility of massive outbreaks,” which could be “catastrophic,” the researchers write. The fact that North African countries are susceptible is particularly concerning, as they currently have little or no malaria and people have no immunity.
The World Health Organization has warned Africa about A. stephensi, calling for active surveillance of mosquitoes. The findings suggest that cities across the continent should take these warnings seriously, says Marianne Sinka, a zoologist at the University of Oxford who led the research.
The maps the team created will be useful for tracking and fighting malaria, says Tamar Carter, a biologist at Baylor University who was not involved in the study. Still, Carter says more research is needed to find out how big the threat is. A. stephensi asks African cities and what is the best way to allocate limited resources to combat it.
