a mosquito from Asia, more urban and resistant to insecticides, worries Africa

Urban mosquito from Asia and resistant to insecticides, theAnopheles stephensi is causing a surge in malaria cases in East Africa, threatening to wipe out decades of progress against the disease on the continent.

The main vector of malaria in Indian and Iranian cities, the species was spotted for the first time in Africa in Djibouti in 2012. This small country in the Horn of Africa, which had then almost eradicated the disease (27 cases that year), has since seen the number of cases rise again to reach more than 70,000 in 2020. The species then arrived in neighboring Ethiopia, triggering, according to the World Health Organization (WHO), a “unprecedented increase” in the number of cases, increasing from 4.1 million (and 527 deaths) last year to 7.3 million (and 1,157 deaths) between 1^is January and October 20, 2024.

This mosquito, which breeds in urban water tanks, gutters and air conditioning equipment, is very resistant to insecticides and bites earlier in the evening than other species, calling into question the role of mosquito nets, a tool the most effective so far against the disease. “The invasion and spread ofAnopheles stephensi can potentially upend the malaria landscape in Africa and reverse decades of progress made in the fight against the disease”estimates Meera Venkatesan, head of the malaria division within the United States Agency for International Development (USAID).

Africa accounted for 95% of the 244 million cases and 608,000 deaths from malaria worldwide in 2022, according to the most recent WHO data.

Lots of unknowns

Experts fear that this urban mosquito could reach densely populated cities, such as Mombasa, Kenya's second city, and Khartoum, Sudan's capital. According to a 2020 study, it could affect 126 million urban dwellers across Africa. Just a month ago, Egypt was declared malaria-free by the WHO after more than a century of fighting the disease, a status that could be at risk if the virus arrives.Anopheles stephensi.

Many unknowns remain about this species. Its presence was confirmed in Kenya in late 2022, but so far it appears to have remained in hot, dry areas without reaching the high-altitude capital Nairobi. “We do not yet fully know the biology and behavior of this mosquito”insists Charles Mbogo, president of the Pan-African Mosquito Control Association: “It’s possible that it’s climate-related and needs high temperatures. Much more research is needed. »

According to him, more funding must be mobilized to capture and study these mosquitoes and to raise awareness of prevention measures, such as covering water containers.

The risk of further spread of the disease comes on top of other worrying trends, such as treatment-resistant malaria seen in Uganda, Rwanda, Tanzania and Eritrea. “The arrival of the resistance [aux médicaments] is imminent »says Dorothy Achu, head of tropical and vector-borne diseases in Africa at the WHO, recalling that the organization is working with the countries concerned to diversify treatment programs and delay this phenomenon. A new variant of malaria is also evading tests used to diagnose the disease.

“The increased transmission caused by Stephensi could potentially contribute to accelerating the spread of other threats”says Meera Venkatesan. Faced with the lack of coordination between African governments, the WHO is working to develop “a more continental approach”explains Dorothy Achu. For Charles Mbogo, above all, there must be “greater political will”. “We share information as scientists with colleagues from neighboring countrieshe said. But we have to reach a higher level. »