Malaria outbreak in Ethiopia was caused by invasive Asian mosquitoes

In early 2022, more than 2,400 people became ill in the Ethiopian city of Dire Dawa, with a spike in malaria cases. The surge in infections is due to the work of an invasive mosquito species spreading across Africa, scientists report.

The findings, presented at the annual meeting of the American Society for Tropical Medicine and Hygiene in Seattle on November 1, indicate that invasive vectors Promotes malaria outbreaksWorryingly, the species may thrive in urban environments, posing the threat of malaria to millions more people across the continent.

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Anopheles stephensi Mosquito native to India and the Persian Gulf and the primary vector. malaria parasite Parasite cause malaria in humans (SN: October 26, 2020).In Africa, the main vector of malaria is Anopheles gambiae. A. Stefensi It was first reported on the African continent in Djibouti in 2012. Since then, the species has appeared in other African countries such as Ethiopia, Somalia and Nigeria.

Fitsum Girma Tadesse, a molecular biologist at the Almauer Hansen Institute in Addis Ababa, Ethiopia, said it was not clear what kind of malaria burden invasive mosquitoes would bring to Africa. In the eight years since the mosquito arrived in Djibouti, the country reported a 40-fold increase in annual malaria cases.but no one directly linked A. Stefensi to increase.

So when malaria cases suddenly increased in Dire Dawa (from 27 to 260 cases in just three weeks in early 2022), Tadesse and his team jumped into the investigation.

Researchers followed 80 patients in the city who sought treatment for malaria at local or university clinics and 210 patients who sought treatment for other reasons, and screened their family members for malaria. did. The team also scanned patients’ neighborhoods for the presence of mosquito adults and larvae within a 100-meter radius of their homes, or dormitories for students visiting clinics.

The team found that malaria patients lived near water sources primarily used by invasive mosquitoes. A. StefensiA home or dormitory close to the habitat A. Stefensi Larvae were 3.4 times more likely to test positive for malaria in family members and boarders than larvae not near such water sources. And most (97%) of the adult mosquitoes the team captured were invasive, the only mosquito species researchers found to carry them. malaria parasite Parasite.

A. Stefensi “They prefer to breed in water reservoirs commonly found in rapidly expanding urban environments,” Tadesse says. native mosquitoes, A. gambiaehe adds, tend to use natural water sources like small pools, which are more common in rural areas. A. Stefensi In parallel with urbanization in Africa, mosquitoes are likely to exploit many new water reservoirs.

“This expands the malaria problem from a predominantly rural one to an urban one,” says Teun Busema, an epidemiologist at Radboud University in Nijmegen, the Netherlands.

A 2020 study by another research group found that if invasive mosquitoes spread widely across the continent, An additional 126 million people could be at risk in urban areas get malaria.

“spread of Anopheles stephensi We are concerned because the species has many traits that make it difficult to control,” said Tanya Russell, a medical entomologist at James Cook University in Townsville, Australia. He was not involved in this research. Not only are insects able to lay eggs in almost any available water source, but the eggs can survive long periods of time even when dry. “

According to Russell, insecticide-treated mosquito nets and indoor spraying of insecticide residues are the main vector control methods for malaria-carrying mosquitoes.but since A. Stefensi Also, when biting outdoors, the spread of mosquitoes can dull the effectiveness of these tools.

The next critical step, Tadesse said, would be interventions to reduce transmission of the deadly parasite, targeting the larval stage of mosquitoes with chemicals and water containers to prevent mosquitoes from laying eggs. This includes encouraging communities to cover and secure

“The window of opportunity to do something about this species is closed,” Boucema says. “So I really think that this requires very urgent action.”