ETHIOPIA — Researchers have discovered new evidence that an invasive species of malaria-carrying mosquito from Asia is spreading in Africa, where it could pose a unique threat to tens of millions of city dwellers.

The insecticide-resistant mosquito could change Africa’s landscape of malaria after research showed it caused an unprecedented urban outbreak in Ethiopia.

“This mosquito’s ability to persist in the dry season and in urban environments has the potential to alter the landscape of malaria in Africa,” said Sarah Zohdy, from the US Centers for Disease Control and Prevention.

An investigation into a steep rise in cases in the Ethiopian city of Dire Dawa during a dry season this year identified the mosquito as the cause of the outbreak.

Scientists say it is the strongest evidence to date that it could prompt surges of malaria in areas typically less affected by the disease.

The eastern city of about 500,000 people is not usually a malaria hotspot, recording just 205 cases in 2019, the scientists said.

But between January and May this year, when rains were patchy and infections would be expected to be low, there were about 2,400 cases.

Ethiopian scientist Fitsum Tadesse presented research that suggests a malaria outbreak in the city of Dire Dawa was “strongly linked” to the invasive Anopheles stephensi species of mosquito.

The species of mosquito is typically found around India and Iran. But in 2012, it was spotted in Djibouti and has now also been found in neighboring Ethiopia, Sudan, and Somalia, as well as in Nigeria.

Most of Africa’s 228 million annual malaria cases are still caused by the Anopheles gambiae mosquito, whose population ebbs and flows seasonally, thriving during the rainy season, especially in rural areas, but declining as a threat during the dry season.

However, Anopheles stephensi has alarmed health officials with its ability to resist some standard insecticides, survive all year, and can thrive in polluted cities

This species can also breed in buckets and open water tanks, meaning that it can survive the dry season. This preference “makes it unique,” Tadesse said.

When the mosquito was first detected in Djibouti in 2012, the country was close to eradicating malaria with just 27 reported cases that year. By 2020, there were 73,000 cases reported in the country.

The number of cases reported in the city jumped from 205 in 2019 to 2,400 in the first five months of 2022 — largely in the dry season.

According to Thomas Churcher, a professor of infectious disease dynamics at Imperial College London who was not connected to the research, the invasive mosquito species could further spread malaria in Africa.

In 2020, 95% of the world’s 627,000 malaria deaths were in Africa. A mosquito vector that is better adapted to large urban areas could make the situation worse.

In commemorating World Cities Day, the World Health Organization said it was launching a new strategy aimed at stopping the spread of malaria in urban areas.

Some scientists are looking to India for potential solutions, such as introducing fish that feed on the mosquito larvae before they hatch, or banning containers with standing water.

More than 40% of the continent’s population lives in cities, and a study published in 2020 predicted that 126 million more people in African cities could be at risk of malaria due to the Anopheles stephensi mosquito.

However, Tadesse cautioned that if the Dire Dawa mosquitoes were elsewhere, that figure could be an underestimate.

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