A malaria outbreak in Ethiopia earlier this year has been linked to an Asian mosquito species. This mosquito is active throughout the dry season, which complicates the fight against its spread.
An invasive mosquito species from Asia has been linked to a malaria outbreak in Ethiopia earlier this year. These insects remain active even during the dry season, when other mosquitoes cannot find water sources to lay their eggs in. The mosquitoes are now invading neighboring countries.
Malaria is a mosquito-borne disease that kills about 627 thousand people every year. Most malaria infections in Africa are spread by the mosquito Anopheles gambiaebut Anopheles stephensi has now also established a foothold on the east coast of the continent. The spread of this invasive species can complicate the eradication of malaria.
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Blood
The presence of A. stephensi was first confirmed in Djibouti in 2012. By then, the country had nearly eradicated malaria. Now Djibouti again has thousands of cases a year.
In the past ten years, the species has spread to Ethiopia, Sudan, Somalia, Yemen and Nigeria. In the spring of 2022, the town of Dire Dawa in eastern Ethiopia saw an increase in malaria from about 200 cases per year to about 2,400 cases, says medical microbiologist Fitsum Tadesse of the Armauer Hansen Research Institute in Ethiopia.
“There was a huge increase in the number of cases, but there was no formal investigation into the cause,” Tadesse says. “So we decided to investigate.” In patients who came to two local clinics in Dire Dawa for malaria, Tadesse and his team screened close contacts for the disease. They also searched for mosquitoes within 100 meters of each household. Their study ran from April to June 2022 and involved about a thousand participants.
Water Repositories
As Tadesse expected, they found a close association between the presence of A. stephensi and the rate of malaria in the city. About 97 percent of the mosquitoes the team found were of this invasive species.
People living in households with water reservoirs, in which the insects can lay eggs, were more than three times more likely to test positive for a malaria infection than people without. Tadesse presented this find on Nov. 1 at a meeting of the American Society of Tropical Medicine and Hygiene in Seattle.
Ramp
Because A. stephensi prefers to lay eggs in the water reservoirs of the inhabitants, in addition to water sources in the open air, it can survive the entire dry season. “Instead of two or three months, the malaria season will last twelve months a year,” says virologist Ayman Ahmen of the University of Khartoum in Sudan, who was not involved in the work.
Without significant investment in preventing the spread of the insects, Ahmen says, ‘we are in for a disaster’.