Mosquito age-grading for malaria vector surveillance in sub-Saharan Africa: current practices and constraints

Background Adult mosquito survival is a critical factor in malaria transmission because Anopheles vectors must live at least 11–14 days before they can transmit. However, there is no direct method to assess age. Traditional methods of mosquito age-grading rely on indirect proxies of reproductive history derived from dissection and observation of ovarian features (Detinova and Polovodova methods). Both approaches are labour-intensive, time-consuming, and demand specialized expertise; with little known about the extent to which are used in malaria surveillance programmes, and why they may be deprioritised. This study assessed current practices, capacity, and constraints related to mosquito age-grading for malaria vector surveillance in Africa, including knowledge and use of existing dissection-based methods and emerging alternatives such as infrared spectroscopy. Methods We conducted an online survey of 285 stakeholders from across Africa, including researchers, entomologists, and National Malaria Programme (NMP) personnel, to assess the practices, priorities, and barriers to mosquito age-grading. This was complemented with a series of in-depth interviews and focus group discussions to collect insights and perspectives from stakeholders regarding their familiarity and use of age-grading methods. Findings: More than 70% of survey respondents reported that malaria vector surveillance was routinely conducted by their institutions or countries, with the highest priority given to vector density, species identification, human biting rate, and insecticide resistance. Familiarity (awareness as opposed to knowledge) of age-grading methods was highest for the Detinova (55%) and Polovodova (44%), and lower for newer approaches, including infrared-spectroscopy. Only 50% of respondents indicated that they regularly assessed mosquito age (mostly Detinova method); with > 1/3 considering age-grading to be a high-priority in vector surveillance. Reported barriers to conducting mosquito-age-grading included insufficient technical expertise, perceived impracticality of ovary dissections for large-scale surveillance, inadequate tools, and limited funding. Conclusions Despite its critical role in malaria transmission, mosquito survival and age are rarely assessed in African vector surveillance programs. There is need for greater acknowledgment of these measures and their implications for disease transmission and control, and investment in tools, training, and funding to overcome current operational barriers. Integrating more practical and scalable age-assessment methods could enhance targeting of interventions.