Researchers warned Tuesday of new evidence that an invasive species of malaria-carrying mosquito from Asia is spreading into Africa, where it could pose a “unique” threat to tens of millions of urban dwellers.
In Africa, home to more than 95% of the world’s 627,000 malaria deaths in 2020, the parasite spreads mostly in rural areas favored by the dominant Anopheles gambiae mosquito population.
However, the Anopheles stephensi mosquito, which has long been the main cause of malaria in Indian and Iranian cities, can also breed in urban water supplies, which means it can thrive during the dry season. It is also resistant to commonly used insecticides.
Modeling research in 2020 found that if Anopheles stephensi were to spread widely in Africa, it would put more than 126 million people in 44 cities at risk of malaria.
Djibouti became the first African country to detect Anopheles stevensi in 2012. It was on the verge of eliminating malaria with only 27 cases reported that year.
However, the number has increased significantly since the arrival of Anopheles stephensi, reaching 73,000 cases in 2020, according to the World Health Organization.
Researchers on Tuesday revealed the first evidence that an outbreak of malaria in neighboring Ethiopia earlier this year was caused by Anopheles stephensi.
In the eastern city of Dire Dawa, a transport hub between the capital, Addis Ababa, and Djibouti, 205 malaria cases were reported in the whole of 2019.
However, more than 2,400 cases were reported this year between January and May. The outbreak was unprecedented because it occurred during the country’s dry season, when malaria is usually rare.
As the numbers rose, Fitsum Girma Tadesse, a molecular biologist at the Armor Hansen Ethiopian Research Institute, and other researchers “set off to investigate.” France Press agency.
They quickly determined that “the Anopheles stephensi mosquito is responsible for the increase in cases,” Tadesse said.
They’ve linked Anopheles stephensi to patients’ infections, and they’ve also found mosquitoes — which carry malaria — in nearby water containers.
Tadesse warned that the mosquito’s preference for open water tanks, which are common in many African cities, “makes them unique”.
The research, which has not been peer-reviewed, was presented at the annual meeting of the American Society of Tropical Medicine and Hygiene held this week in Seattle, US.
Preliminary results were also presented at the conference, which identified Anopheles stevensi in 64% of the 60 test sites in nine states of neighboring Sudan.
“In some cases, we found that up to 94% of households had Stephensey mosquitoes,” Hamouda Kafi, head of the Integrated Vector Management Department at the Sudanese Ministry of Health, said in a statement.
The findings come after the Nigerian Institute of Medical Research confirmed in July that it had detected Anopheles stephensi in West Africa for the first time.
It was “surprising” to discover the mosquitoes so far west, where the focus was on the Horn of Africa, Sarah Zuhdi, an Anopheles Stephensey specialist at the US Centers for Disease Control and Prevention, told AFP.
Zohdi said it had been proven in the past two months that Anopheles Stephensey “was no longer a potential threat” in Africa.
“In the Ethiopian context, this is a threat — we now have data to show that,” said Zuhdi, who also works with the US President’s Malaria Initiative, a partner in the Dire Dawa study.
“The evidence is out now that this is something the world needs to work on,” she added.
Anopheles stephensi has reportedly been detected in Somalia, according to the World Health Organization, which in September launched an initiative aimed at stopping the spread of mosquitoes in Africa.
Because Anopheles stephensi can thrive in urban water tanks, “you go from a seasonal disease to one that can last all year,” Zuhdi said.
She added that this shift posed a “significant threat” to the recent gains made against malaria.
Malaria deaths more than halved from the turn of the century through 2017—largely due to insecticide-treated nets, testing, and medication—before progress stalled during the COVID-19 pandemic.
Zohdi called for increased surveillance to see how widespread Anopheles stephensi was across the continent.
“The true extent of the mosquito spread is unknown,” she said.