Building resilience against the growing threat of arboviruses: a scoping review of Aedes vector surveillance, control strategies and insecticide resistance in Africa.

BACKGROUND

The number of reports of arboviral outbreaks is increasing and, consequently, the need for effective surveillance and vector control plans for Aedes-borne diseases is becoming more urgent. To explore the current state of knowledge of Aedes arbovirus vectors in Africa, we reviewed studies published between 1980 and 2023 that involved Aedes vector surveillance, vector control or insecticide resistance, with the aim to synthesize information and identify knowledge gaps to guide future Aedes research and control in Africa.

METHODS

Studies conducted in Africa and published between 1980 and 2023 were retrieved from twelve electronic databases using search strings designed to capture relevant concepts. Articles that did not meet the eligibility criteria were excluded during relevance screening.

RESULTS

Out of 17,337 publications identified, 877 full-text articles were reviewed, of which seven included information on vector surveillance, 56 on vector control and 57 on insecticide resistance. Publications reporting longitudinal data from sustained Aedes vector surveillance systems were only available for Senegal and La Réunion. Aedes vector control studies were principally controlled bioassays or small-scale studies conducted before and after entomological studies which lacked epidemiological outcomes. The most studied methods were larval control (n = 21 publications), integrated control combining different interventions (n = 7), topical repellents (n = 6), environmental management (n = 5) and spatial repellents (n = 3). Four publications described typical vector control responses during arbovirus epidemics in Africa: these often combined larviciding, ultra-low volume (ULV) space spraying and community engagement to reduce larval sites, alongside active source reduction. There was a lack of high-quality evidence generated through rigorous study design on the effectiveness of control measures in reducing arbovirus transmission in the African context. As a consequence, the scientific basis for evidence-informed decisions in Africa, both for routine Aedes vector control or for outbreak response, remains weak. Insecticide resistance studies focused on adulticides using WHO tube tests (n = 43 publications), with larval bioassays relatively less common (n = 13). Aedes aegypti (n = 53) and Aedes albopictus (n = 12) were the only Aedes species tested. The most commonly tested adulticides were permethrin and deltamethrin (pyrethroids); bendiocarb (carbamate); and dichlorodiphenyltrichloroethane (DDT; organochlorine), although the results were rarely reported in connection with decision-making about Aedes control. Results of the most relevant adulticides indicated that Ae. aegypti populations were generally susceptible to malathion (organophosphate), but resistance to permethrin and deltamethrin was detected in West and Central Africa. Most studies pre-dated the revised WHO guidance, and insecticide concentrations were mostly those recommended for Anopheles susceptibility testing that use relatively higher discriminating doses, and thus likely underestimate true Aedes resistance levels. Larval susceptibility bioassays were conducted with temephos (n = 12) and Bacillus thuringiensis israelensis (n = 6). Temephos resistance was only detected in Cabo Verde following several decades of use.

CONCLUSIONS

Given the increasing frequency of arbovirus epidemics in Africa, countries urgently need to develop plans for emergency response and robust control strategies that make use of evidence from good-quality studies to strengthen resilience.