A mosquito species capable of transmitting malaria in urban areas has spread rapidly, raising concerns about an increase in malaria risk throughout East Africa, according to researchers.

The Asian malaria mosquito Anopheles stephensis has been confirmed in seven counties since its initial detection in December 2022, representing a significant geographic expansion that could alter malaria transmission patterns in the region.

“This invasive vector could pose a significant public health threat, particularly in urban and peri-urban areas of Kenya,” lead researcher from Kenya Medical Research Institute (KEMRI) and senior author of the study, published in a scientific report, Dr Eric Ochomo, stated.

Multiple introductions

The findings reveal that the mosquito has established populations along major transportation routes in Marsabit, Turkana, Mandera, Wajir, Isiolo, Samburu and Elgeyo Marakwet counties, areas that historically had low malaria transmission rates.

Genetic analysis of 147 mosquito samples revealed three distinct genetic compositions, indicating multiple separate introductions into Kenya rather than spread from a single source.  

The genetic fingerprints closely match mosquito populations in southern Ethiopia, suggesting cross-border movement along trade routes.

“The genetic connectivity between Kenyan Anopheles stephensi and populations in neighbouring countries emphasises the need for coordinated, cross-border surveillance and control efforts,” Ochomo said.

Unlike native African malaria mosquitoes that typically breed in rural natural water sources, Anopheles stephensi thrives in urban environments by using artificial water storage containers, discarded tires and construction sites for breeding.  

This adaptability makes it particularly dangerous for Kenya’s growing urban centres.

The World Health Organisation launched a special initiative in 2022 specifically to combat the spread of this invasive species, which can transmit Plasmodium falciparum and Plasmodium vivax malaria parasites and has shown resistance to all classes of insecticides used against adult mosquitoes in the region.