By Syriacus Buguzi, Fiona Broom
Africa has just months to react to an invasive malaria mosquito that thrives in cities, before the situation escalates beyond control, experts warn.
Scientists predict that more than 125 million city dwellers across Africa will face a higher malaria risk from a type of Asian mosquito that is quickly moving across the continent.
The mosquito, Anopheles stephensi, is one of the few malaria mosquitoes that thrives in urban areas because of its ability to find clean water to lay its eggs.
Malaria is traditionally considered to be a rural disease. In Africa, city centres can be completely free of malaria transmission, according to experts from the London School of Hygiene and Tropical Medicine (LSHTM).
But, the invading mosquito could drastically alter the location and movement of malaria in Africa, which records 94 per cent of global malaria deaths, mostly in children under five.
“I think it’s really quite scary,” says Jo Lines, professor of malaria control and vector biology at LSHTM. “It’s part of our duty as [scientists] to be saying: ‘Look here, something’s happening here.’ If we don’t shout now it will be too late.”
New research led by Marianne Sinka, a senior postdoctoral researcher at the University of Oxford, says that An. stephensi may already be adapting to its new environment and becoming active year-round.
“If it continues its incursion into the African continent unchecked, there is a very real possibility of mass outbreaks of malaria,” Sinka’s team says. “In a continent striving to improve and strengthen its health systems, such a huge burden could be catastrophic. Targeted vector surveillance is therefore urgently needed.”
Sinka’s research is a warning bell, says Louisa Messenger, an assistant professor at LSHTM. “The key conclusions and observations are very striking. The numbers, if they turn into reality, are very dramatic,” Messenger tells SciDev.Net.
In 2012, an unusual outbreak of urban malaria was reported in the Horn of Africa’s Djibouti City, with Ethiopia and Sudan also reporting cases. This was the first recorded appearance of An. Stephensi in Africa.
By last year, the World Health Organization had issued a vector alert, warning that the mosquito seemed to be spreading from Djibouti to neighbouring countries.
Messenger says the mosquito likely arrived via ships entering ports in eastern Africa. Transmission mapping shows the mosquito’s spread follows the major transportation routes used by heavy vehicles to move freight.
“The incursion of An. stephensi into Africa is particularly worrying; over 40 per cent of Sub-Saharan Africans live in urban environments,” Sinka and co-authors write in their paper, published in PNAS (14 September).
“Within urban environments, mosquitoes can be much more difficult to control yet people may have better access to healthcare and treatment, so it is difficult to estimate what the consequences of this invading mosquito could be,” Sinka tells SciDev.Net.
Researchers are working fast to understand the scale of the spread of An. stephensi.
“The more you look, the more you find,” Messenger says. “We don’t really understand the magnitude