Invasive mosquitoes could fuel malaria upsurge in Africa

A new study has linked an invasive insecticide-resistant mosquito to an unprecedented urban outbreak of malaria in Ethiopia and warned that it can fuel an upsurge of cases in various African countries. Known as Anopheles stephensi, the mosquito species is native to South Asia and has long been the primary transmitter of malaria in urban areas of India and Iran, but was never seen in Africa until 2012, when it was reported in Djibouti. At that time, Djibouti was close to eliminating the disease, but unfortunately, the following year, the country experienced an upsurge of cases that are suspected to have reached 40-fold. The study presented by the American Society of Tropical Medicine and Hygiene (ASTMH) this week, suggested that this particular type of mosquito was significant in the rise of cases in Djibouti, it is the one that has recently fuelled an outbreak in Ethiopia. The outbreak occurred in Dire Dawa, a city of about 500,000 people in eastern Ethiopia that typically records only about 200 cases a year, but between January and May 2022, about 2,400 cases were reported. An investigation by experts found that the mosquito species is resistant to insecticides most commonly used to control malaria via treated bed nets and indoor insecticide spraying, and can survive in hot climatic conditions. “Malaria in Africa is typically associated with rainy seasons in rural areas, but this mosquito produced a 10-fold spike in malaria infections in just three weeks in an urban area during a dry season,” said Fitsum Tadesse, a molecular biologist with the Armauer Hansen Research Institute in Addis Ababa. “Also, unlike the mosquitos that typically transmit malaria parasites in Africa, this one is best known for its ability to thrive in man-made water storage containers like what you see in rapidly expanding urban neighbourhoods,” he added. Most malaria cases in Africa are caused by a mosquito species known as Anopheles gambiae, whose populations always fall when the rainy seasons fade away. Having been the source of the Dire Dawa outbreak, coupled with recent evidence of Anopheles stephensi mosquitoes thousands of miles away in Nigeria in West Africa, the ASTMH has suggested that this raises concerns of “a new front opening up in Africa’s long-running battle against malaria.” Speaking to The New Times, Dr Emmanuel Hakizimana, the Director of Vector Control at Rwanda Biomedical Centre (RBC), said all African countries are at risk of malaria but noted that the particular mosquito species has not been identified in Rwanda. He added that there is a need for extended surveillance to ensure that such mosquitoes are anywhere in the country and identified, reiterating that medics and researchers are currently doing various researches about mosquitoes in the country. Africa suffers 95 per cent of the world’s 627,000 annual malaria deaths, and most victims are children under age 5. Sarah Zohdy, a disease ecologist and Anopheles stephensi expert with the U.S. Centres for Disease Control and Prevention (CDC), said the stephensi mosquito species “is not like any other malaria-carrying mosquito we have seen in Africa before.” She added: “This mosquito’s ability to persist in the dry season and in urban environments has the potential to alter the landscape of malaria in Africa,” she said. “It could cause malaria to expand from a predominantly rural disease to both a rural and urban challenge that also impacts Africa’s rapidly growing and densely populated cities, where infection rates have been comparatively low.” According to statistics from RBC, Rwanda recorded a drop in malaria incidence from 400 per 1,000 in 2016 to 89 per 1,000 in 2021. Malaria cases also fell from 5 million in 2016 to 1 million in 2021, in addition to a decrease in severe malaria from 18,000 in 2016 to less than 2,000 in 2021, while malaria-related deaths reduced from 700 in 2016 to 69 in 2021.

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Invasive mosquitoes could fuel malaria upsurge in Africa