Malaria: an invasive species of mosquito is gaining ground in Africa

Malaria: an invasive mosquito species is gaining ground in Africa


New data show the spread in Africa of an invasive species of mosquito vector of malaria from Asia, posing a potential threat to tens of millions of city dwellers, alert researchers Tuesday.< /strong> 

Caused by five species of parasites transmitted by the bites of infected mosquitoes, malaria (or malaria) remains a scourge, especially for African children, despite the recent arrival of a vaccine. It manifests as fever, headache, muscle aches, followed by cycles of chills, fever and sweats.

In Africa, where more than 95% of the world's 627,000 deaths have occurred of malaria in 2020, the disease is spreading mainly in rural areas, via Anopheles gambiae mosquitoes, which are dominant on this continent.

However, another species, Anopheles stephensi, long the main vector of malaria in Indian and Iranian cities, can breed in urban water reservoirs, and therefore thrive during dry seasons. It is also resistant to common insecticides.

If this mosquito were to spread widely in Africa, more than 126 million people in 44 cities would be at risk of malaria, according to a 2020 model. 

In Djibouti, the first African country to detect Anopheles stephensi in 2012 when it was on the verge of eradicating malaria with only 27 cases that year, malaria has skyrocketed since the arrival of this pathogen. Some 73,000 cases were recorded there in 2020, according to the World Health Organization.

And an outbreak of malaria in neighboring Ethiopia was caused by the same mosquito, according to a non-peer-reviewed study, presented Tuesday at the annual meeting of the American Society of Tropical Medicine and Hygiene in Seattle, USA.

In Dire Dawa, the second largest city in Ethiopia, located in the east, on the railway line between Addis Ababa and Djibouti, 205 cases of malaria were recorded in 2019. This year, more than 2,400 cases were reported between January and May alone.

The outbreak occurred during the dry season, when malaria is traditionally rare.

Faced with the surge in cases, researchers “hastened to investigate”, told AFP one of them, Fitsum Girma Tadesse, molecular biologist at the Armauer Hansen research institute in Addis Abeba. They quickly determined that “Anopheles stephensi mosquitoes are responsible for the increase in contamination”.

“Major threat”

These mosquitoes carry malaria were also found in nearby water reservoirs.

The predilection of this species for open water reservoirs, common in African cities, “makes it unique”, underlined Fitsum Girma Tadesse.

Sudan also seems to be affected. According to other preliminary data presented in Seattle, Anopheles stephensi mosquitoes were identified in 64% of 60 testing sites, spread across nine regions.

“In some cases, up to 94% of households have stephensi mosquitoes” nearby, Hmooda Kafy, a medical entomologist and head of the vector management department at the Sudanese Ministry of Health, said in a statement. 

The findings come after the Nigerian Institute of Medical Research first confirmed the presence of Anopheles stephensi in West Africa in July. 

For Sarah Zohdy, Central disease control, it was “surprising” as the focus was on the Horn of Africa.

In recent months, the threat of Anopheles stephensi in Africa is no longer “potential”, but proven, noted this expert in disease ecology, who works with the United States Presidential Malaria Initiative, a partner of the Ethiopian study. 

“The evidence now exists to suggest that the world needs to act against this phenomenon,” she insisted, also calling for increased monitoring to know exactly how far the 'Anopheles stephensi has spread across the African continent. It is believed to have been spotted in Somalia, according to the WHO, which in September launched an initiative to counter its spread in Africa. 

Because it can thrive in urban water reservoirs, from a seasonal disease to one that can persist year-round,” posing “a major threat” to progress against malaria, according to the researcher.

Malaria deaths have fallen by more than half between the turn of the century and 2017—mainly thanks to insecticide-treated bed nets, tests and drugs—before the Covid-19 pandemic halted this decline.