Hidden Malaria Mosquito Resurfaces in Angola After Decades of Obscurity

For more than half a century, a mosquito first described from Angola in 1969 has slipped almost entirely through the nets of science. Anopheles azevedoi, a member of the obscure Paramyzomyia series of anopheline mosquitoes, was so frequently confused with other species that researchers could barely say where it lived, how it behaved, or whether it posed any threat to human health. A new study published in the journal Parasites & Vectors has now pulled this shadowy insect into the light, mapping it along a broad stretch of the Angolan coast, publishing the first DNA markers that allow unambiguous identification, and revealing a troubling trait: populations of the species have developed resistance to the insecticides most commonly used against malaria vectors.

The research, led by Gonçalo Alves of The MENTOR Initiative and the Instituto de Higiene e Medicina Tropical at Universidade NOVA de Lisboa, together with Cátia Marques of Population Services International and an international team spanning the US Centers for Disease Control and Prevention, the US President’s Malaria Initiative, Angola’s National Malaria Control Program and provincial health authorities, drew on entomological surveillance carried out between 2015 and 2022. Field teams worked in four provinces that trace the Atlantic coastline of Angola: Luanda, Benguela, Cuanza Sul and Namibe. The work was approved by Angola’s National Institute for Health Research and funded through a constellation of international donors, including USAID’s President’s Malaria Initiative and The Global Fund, reflecting the practical stakes of the question at hand.

Correct species identification sits at the heart of malaria control. Public health campaigns spray walls with residual insecticides, distribute bed nets and deploy larval-source management, all calibrated against the known habits of the mosquito species that transmit Plasmodium parasites. When a species is routinely misidentified, those calibrations go wrong. An. azevedoi has long been one of the casualties of this confusion, its adults difficult to distinguish morphologically from related anophelines and its biology so poorly documented that surveillance programs had little reason to pay it attention. The new study set out to correct the record by combining traditional morphology with two molecular markers: the internal transcribed spacer 2 (ITS2) region of nuclear ribosomal DNA and the mitochondrial cytochrome c oxidase subunit I (COI) gene, both workhorses of insect barcoding.

The results confirmed that An. azevedoi occupies a surprisingly broad and varied range. The species was found in multiple habitats along the Atlantic coast of Angola, with new geographical records in Luanda and Benguela provinces expanding its known distribution. Perhaps more striking was the setting: the mosquito turned up frequently in urban and peri-urban environments, a habitat association that matters enormously in a country where cities such as the capital Luanda have grown explosively and where urban malaria transmission has become an increasing concern for control programs. A mosquito that thrives near human settlements is, by definition, a mosquito that control measures must account for.

To understand whether the species actually feeds on people, the researchers screened a subset of wild-caught adults for blood-meal sources. Human blood was identified in three field-collected specimens, offering the first direct evidence that An. azevedoi bites humans in the study area. The team also tested the mosquitoes for Plasmodium infection, and importantly, none of the screened adults carried the malaria parasite. That absence does not declare the species a non-vector; it simply means that, in this sample, no infections were detected. Determining whether An. azevedoi contributes to malaria transmission will require larger screens, but the demonstration of human blood feeding alone is enough to justify closer attention.

The most consequential findings, however, concern insecticides. Using World Health Organization tube bioassays and bottle bioassays on live mosquitoes reared from field-collected larvae, the team measured the susceptibility of An. azevedoi populations to the major classes of public health insecticides. The outcome was sobering: the species exhibited resistance to pyrethroids, the chemical class that impregnates the vast majority of insecticide-treated bed nets, and to DDT, an organochlorine still used in some indoor residual spraying programs. Resistance to two different insecticide classes signals that the standard toolkit of vector control is losing traction against this mosquito wherever it occurs.

Yet the bioassays also contained a note of hope. Two populations from Luanda remained fully susceptible to chlorfenapyr, a pyrrole insecticide with a distinct mode of action that disrupts energy production in mosquito cells and is increasingly deployed in new-generation treated nets and indoor residual formulations precisely because it can overcome pyrethroid resistance. That chlorfenapyr retains activity against these An. azevedoi populations gives Angolan control programs a concrete, evidence-based option should the species ever prove to be a significant player in transmission, and it illustrates a broader principle: knowing the susceptibility profile of every locally relevant species, not just the classic primary vectors, is essential when resistance reshapes the landscape.

Methodologically, the study offers a template for rescuing other neglected species from taxonomic obscurity. Larvae were collected in the field and reared to adulthood so that live specimens of known provenance could be used in the bioassays, avoiding the ambiguity that comes with testing damaged or variable wild adults. Adults were first identified morphologically and then confirmed by sequencing ITS2 and COI, and the authors have made these markers publicly available for the first time, meaning that any laboratory in the region can now verify an identification of An. azevedoi with a simple PCR and sequencing workflow. In a genus where cryptic species complexes routinely confound surveillance, the publication of validated reference sequences is a quiet but genuinely transformative contribution.

The collaboration behind the work is itself noteworthy, uniting Angola’s National Malaria Control Program and provincial health directorates in Benguela, Cuanza Sul and Sumbe with international partners, and crediting specialists such as John Gimnig at CDC Atlanta for taxonomic determination and Adeline Chan, the PMI entomologist in Angola during 2015 and 2016, for coordinating surveillance and preserving field specimens. The funding came from USAID through the President’s Malaria Initiative via projects including AIRS, VectorLink and Health for All, and from The Global Fund through the NMF3 Angola grant, with additional support from the Portuguese Foundation for Science and Technology. The authors stress that the funders played no role in the design, analysis or publication of the study, and that the findings do not necessarily represent the official positions of USAID, PMI or the CDC.

What emerges is a call to widen the surveillance lens. Malaria control in sub-Saharan Africa has understandably focused on the dominant vectors, chiefly members of the Anopheles gambiae complex and the Anopheles funestus group, whose efficiency as parasite carriers has shaped a half-century of strategy. But as primary vectors come under increasing pressure from insecticides and as urban transmission complicates the epidemiological picture, secondary and previously ignored species may occupy ecological space left vacant by successful interventions. An. azevedoi, feeding on humans in cities and peri-urban districts, already resistant to pyrethroids and DDT yet vulnerable to newer chemistries, exemplifies exactly the kind of species that deserves routine monitoring rather than perpetual misidentification. The authors argue for including it in future entomological surveillance and for research into its potential public health relevance, and the tools to do so now exist. After 57 years in the taxonomic shadows, one of Angola’s overlooked mosquitoes finally has a name that can be checked, a map that can be read and a susceptibility profile that can inform decisions, and the study stands as a reminder that in the fight against malaria, the mosquitoes you do not know may matter as much as the ones you do.

Subject of Research: Distribution, molecular identification and insecticide resistance of the malaria mosquito Anopheles azevedoi in Angola

Article Title: Anopheles azevedoi (Ribeiro, 1969) in Angola: new geographical records, molecular characterization, and insecticide susceptibility profile of a commonly misidentified species

Article References: Anopheles azevedoi (Ribeiro, 1969) in Angola: new geographical records, molecular characterization, and insecticide susceptibility profile of a commonly misidentified species. (n.d.). https://doi.org/10.1186/s13071-026-07706-5

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07706-5

Keywords: Anopheles azevedoi, Angola, malaria, mosquitoes, insecticide resistance, pyrethroids, DDT, chlorfenapyr, COI barcoding, ITS2, vector surveillance, urban malaria