The Kenya Medical Research Institute (KEMRI) is currently running surveillance across multiple counties to track the spread of a new malaria vector, Anopheles stephensi, which is emerging as a significant public health concern in Kenya. Field teams comprising entomologists, drivers and community health promoters are actively collecting mosquito larvae from identified breeding sites in both rural and peri-urban areas, using GPS-enabled tools to map and document locations.  

In Syokimau, Machakos County, community health promoters are collecting larvae from stagnant artificial water bodies such as excavated pits, tyres, construction sites, and car washes. These environments are increasingly important because Anopheles stephensi thrives in artificial water storage and urban habitats, unlike traditional malaria vectors that prefer more natural ecosystems. The surveillance teams use standardised collection tools, including larval dippers and pipettes, and store samples in labelled tubes with alcohol for transport and analysis.  

The vector, originally from South Asia and the Arabian Peninsula, was first detected in Africa in Djibouti in 2012. Its establishment there coincided with a sharp resurgence of malaria cases, rising from near elimination levels to tens of thousands of infections. It has since been reported in multiple African countries, including Ethiopia, Sudan, Somalia, Nigeria and Ghana. In Kenya, it has been confirmed in several northern, coastal, and arid counties, including Wajir, Garissa, Lamu, Tana River, Isiolo, Turkana, Samburu, Baringo, Elgeyo Marakwet, Kitui, and Mandera. Surveillance suggests it is spreading along transport corridors, raising concerns about rapid geographic expansion.  

The vector has not yet been confirmed to carry malaria parasites in Kenya. Still, its presence alone is considered a high-risk development due to its demonstrated capacity, elsewhere, to increase transmission significantly. Kenya’s dominant malaria vectors remain Anopheles gambiae, Anopheles arabiensis, and Anopheles funestus. Still, the introduction of a new, urban-adapted species could alter transmission dynamics, particularly in densely populated and fast-growing settlements.  

Field observations indicate that Anopheles stephensi is closely linked to human activity. It is frequently found in artificial water containers and stagnant water created through poor drainage, construction activity and household water storage practices. It does not thrive in flowing water, making urban infrastructure and waste management practices key determinants of its breeding success. This reinforces the assessment that human behaviour and environmental modification are directly contributing to its spread.  

Once collected, samples are transported to KEMRI laboratories for detailed analysis. This includes morphological identification, genetic testing using Polymerase Chain Reaction (PCR), and dissection of mosquito parts to determine blood meals and infection status. These processes help distinguish species and confirm the presence of Anopheles stephensi, and assess whether it is carrying malaria parasites. The surveillance system also integrates digital tracking through QR codes and GIS mapping.  

Despite technical progress, field teams face operational constraints, including poor road networks, security risks in certain regions, and logistical challenges that require extended travel and field stays. Nonetheless, surveillance has already identified more than 50 breeding sites nationwide.  

Experts caution that early detection alone is not sufficient. The key concern is the vector’s potential to establish itself in urban environments and replicate the Djibouti pattern of rapid malaria resurgence. Understanding its ecology, modes of transmission, and interactions with human activity is now central to Kenya’s malaria control strategy.  

(Source: Daily Nation)