Dangerous West African mosquito found in Kenya

A West African malaria mosquito has been found in Kenya for the first time.

Scientists say the finding is important because this mosquito, known as Anopheles coluzzii, is highly competent and can tolerate more arid conditions and thrive in both rural and urban settings.

The mosquito was confirmed in Turkana, where the Asian mosquito Anopheles Stephensi was also detected three years ago.

The new finding was reported by researchers from the Kenya Medical Research Institute (Kemri) and its partners.

"This vector is potentially contributing to malaria transmission in Turkana county and malaria control interventions currently in place may be ineffective against it,” they said in a paper published by the Malaria Journal on Friday.

They sampled mosquitoes collected across five malaria epidemiological zones in Kenya since 2006, and conducted genome sequencing on them.

Surprisingly, An. coluzzii was detected in Turkana across all sampling periods, confirming its presence in the country since 2006. This revelation challenges previous assumptions about the distribution of malaria vectors in Kenya.

Coluzzii mosquito is the main vector in West and Central Africa and this is the first time it has been confirmed in Kenya.

Notably, the researchers also uncovered high frequencies of mutations associated with insecticide resistance, particularly to DDT and pyrethroids in the Kenyan populations.

“Variants conferring stronger pyrethroid resistance could compromise the efficacy of new pyrethroid + PBO long-lasting insecticidal nets (LLINs), currently considered among the most effective defence against resistant populations,” said the main authors – Kemri’s Luna Kamau and Kelly Bennett of Malaria Vector Genomic Surveillance, Wellcome Trust Sanger Institute, UK.

Their paper is titled: “The Anopheles coluzzii range extends into Kenya: detection, insecticide resistance profiles and population genetic structure in relation to conspecific populations in West and Central Africa.”

The Turkana samples came from Kakuma refugee camp, a highly populated region that experiences low level local transmission but has recently suffered recurrent epidemics.

Historically, the area has received little attention regarding malaria intervention, because the climate was considered unsuitable for known vector species, except An. arabiensis, considered a less competent vector.

The researchers now suspect the Western Africa mosquito could be a culprit in recent waves of malaria in Turkana.

That is because coluzzii has also been documented in Somalia, which shares a similar arid to semi-arid ecosystem, meaning the Kenyan populations are not isolated.

“This finding alongside the recent finding of An. stephensi in Turkana and other regions of northern Kenya emphasises the need for re-evaluation of the distribution, bionomics and epidemiological significance of the local vector populations in the country,” the researchers said.

They added: “This is the only way the country will be able to ensure vector control approaches are sufficiently targeted at the myriad of Anopheles vectors responsible for transmission in the different settings in Kenya.”

In Kenya, approximately 70 per dent of the population is at risk of malaria with the disease accounting for an estimated 13–15 per cent of outpatient consultations.

The disease kills about 10,000 Kenyans every year, mostly children, according to various estimates.

Historically, the Anopheles gambiae species complex and Anopheles funestus group have been known to transmit malaria in Kenya.

Within the An. gambiae complex, An. gambiae sensu stricto and Anopheles arabiensis were considered the major vectors, with Anopheles merus contributing to transmission in coastal Kenya.

Anopheles coluzzii is another member of the An. gambiae species complex.

“Past failure to detect An. coluzzii in Kenya is likely associated with the fact that malaria vector surveillance and identification has tended to focus on historically known primary vectors using species-specific markers,” the researchers said.