Malaria exploded this year in the Ethiopian city of Dire Dawa, which saw more than 10 times as many cases between January and May as it did in all of 2019.

What made this spike in cases unusual is that it happened outside the rainy season, when malaria typically surges across Africa, and in an urban area — malaria is more of a rural problem on the continent. Cities are not immune, but they typically don’t see these kinds of outbreaks.

Something new and insidious has arrived in the Horn of Africa. An invasive species of mosquito called Anopheles stephensi threatens to unravel two decades of gains in malaria control. And it may bring the deadly disease to more of the continent’s rapidly growing cities.

“There is real fear that it could start more transmission in these areas that traditionally don’t have as much malaria,” said Arran Hamlet, a disease modeling expert with the Imperial College London. “And they don’t have infection control strategies implemented to the same levels.”

The new mosquito arrives at a bad time in the fight against malaria.

Africa’s native mosquitoes have become increasingly resistant to insecticides. (Anopheles stephensi is already resistant.) In addition, the malaria parasite is getting not only tougher to kill, but tougher to spot. Malaria strains that don’t show up on rapid diagnostic tests are becoming more common.

“We don’t want the three to meet — the drug resistance, the diagnostic resistance and the highly efficient vector [Anopheles stephensi],” said Fitsum Girma Tadesse, a molecular biologist at Ethiopia’s Armauer Hansen Research Institute.

“What happens if they coexist? We don’t know,” he said. “It’s really dangerous. You can’t detect the parasite. You can’t kill it with a drug. And the mosquito is wise enough to evade your [control] mechanisms.”

Fitsum and his colleagues linked Anopheles stephensi to the Dire Dawa outbreak in a study presented at the American Society of Tropical Medicine and Hygiene in Seattle this month. It is the strongest evidence yet that the mosquito is increasing malaria rates in Ethiopia.

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