Abstract
Introduction : Despite considerable progress in malaria control, challenges remain because of spreading resistance to insecticides and antimalarials. Moreover, idiosyncracies in vectors biting behaviour can lead to persistent transmission despite effective implementation of control interventions based on insecticidal nets. Malaria is more prevalent in rural as opposed to urban areas. However, urban malaria may increase in the future due to adaptation of malaria vectors to urban conditions. Here, we investigated biting of malaria vectors along an urbanisation gradient to gain insights into the emerging issues of urban malaria and vector behaviour in residual transmission.Methods : We assessed biting rates in three localities next to and within Ouagadougou, Burkina Faso, each locality representing urban, peri-urban, and rural environments. Human volunteers conducted landing collections during 3 months of the 2023 rainy season. In order to determine the relative contribution to transmission of indoor versus outdoor biting, as well as daytime versus nighttime biting, each sampling occasion consisted of parallel indoor and outdoor collections during 48 hours round-the-clock.Results : The distribution of 4,428 Anopheles gambiae s.l. across indoor/outdoor sites and daytime/nighttime periods varied between urban and non-urban settings. In the urban area outdoor landings accounted for >2/3 of the total, whereas in non-urban settings this proportion decreased to ~1/2. Diurnal samples taken indoors contributed 13-19% of biting in non-urban sites. Assuming a transmission season of 100 days and average mosquito infectiousness of 1% (assessment underway), we expect ~90 and ~1 infectious bites/person/year outdoors in the urban locality, and during daytime in non-urban settings, respectively.Conclusions : Growing evidence indicates limitations in malaria control interventions relying on nocturnal indoor biting by vectors. Besides insecticide resistance, the strength of diurnal and/or outdoor biting can set a ceiling to the effectiveness of insecticide-treated nets, suggesting considering vector control strategies against residual transmission in malaria elimination efforts.