An invasive mosquito species capable of transmitting malaria in urban environments is spreading rapidly across Kenya, raising concerns about a significant shift in malaria transmission patterns in East Africa. The mosquito, Anopheles stephensi, originally native to South Asia and the Middle East, has now been confirmed in seven counties across Kenya, marking a notable expansion since its first detection in December 2022.
The spread of Anopheles stephensi is alarming due to its unique ability to adapt to urban and peri-urban environments, unlike native African malaria vectors that typically breed in rural, natural water sources. This mosquito thrives in artificial containers such as water storage tanks, discarded tires, and construction sites making densely populated cities and towns particularly vulnerable.
The presence of the mosquito has now been documented in Marsabit, Turkana, Mandera, Wajir, Isiolo, Samburu, and Elgeyo Marakwet counties. These regions have historically recorded lower malaria transmission rates, but the establishment of Anopheles stephensi populations could change that trend dramatically.
What makes this development even more concerning is the evidence of multiple separate introductions into Kenya. A genetic analysis of 147 mosquito samples revealed three distinct genetic variations, suggesting that the mosquito did not spread from a single source. Instead, the findings indicate several independent introductions, likely facilitated by cross-border trade and movement.
Genetic similarities between the Kenyan populations and those found in southern Ethiopia point to the possibility that the mosquito is entering Kenya through major transport and trade routes, highlighting a regional issue that requires a collaborative response. The interconnected nature of these populations underscores the urgency for cross-border coordination in monitoring and controlling the spread of this species.
Anopheles stephensi is known to transmit both Plasmodium falciparum and Plasmodium vivax malaria parasites. Its ability to flourish in urban settings represents a potentially devastating shift in the malaria landscape, particularly as African urban populations continue to grow. Traditionally, malaria has been largely a rural disease in sub-Saharan Africa. The adaptation of this vector to urban conditions challenges existing control strategies that have focused primarily on rural transmission.
Compounding the problem is the mosquito’s demonstrated resistance to all major classes of insecticides currently used to target adult mosquitoes in the region. This resistance reduces the effectiveness of traditional control measures such as indoor residual spraying and insecticide-treated nets, potentially undermining decades of progress in malaria control and prevention.
The World Health Organization has recognized the threat posed by Anopheles stephensi and in 2022 launched a targeted initiative to curb its spread. However, experts warn that more robust action is needed, including intensified surveillance, improved data-sharing across borders, and public awareness campaigns focusing on eliminating potential breeding sites in urban areas.
Kenya faces a critical moment in the fight against malaria. With Anopheles stephensi taking hold in new regions and demonstrating resilience against conventional control tools, innovative and regionally coordinated strategies will be essential to prevent a resurgence of malaria in areas previously considered low-risk. The continued expansion of this vector threatens to reshape malaria transmission in East Africa, demanding urgent attention and collaboration from governments, health agencies, and communities alike.
