Mosquito hunters: tracking, trapping and mapping to outsmart malaria

By Duncan Kobia

Mosquitoes have been around for over 200 million years. So having the capacity to evolve to ensure survival is quite literally in their DNA.?

More recently, those of us working to defeat malaria have seen mosquitos change their behaviour and develop resistance to the insecticides that we have relied on to stop the spread of the disease. While malaria is still only transmitted to humans by the female mosquitoes of the genus Anopheles, the rise of invasive species within that genus – such as An. stephensi – is an important reminder that effective surveillance is imperative if we are to get ahead of these smart shape-shifters.?

Just as the mosquitoes themselves are evolving to expand their geographic location and change their biting and resting behaviours, so must we continue to innovate in our surveillance approach and methodology. How and where to carry out surveillance is not one-size-fits-all. Various trapping techniques are used to monitor malaria vectors, each tailored to different aspects of vector biology and backed by research. Decisions about where to deploy the traps generally rely heavily on expert opinions and assessments. Is there a better way??

With the recent progress in geostatistical and classification methods and their application in ecology, there is a growing body of evidence that could support improvements in malaria surveillance. One such study uses environmental factors from remote-sensed data, historical mosquito surveillance data, and geostatistical methods and classification techniques to stratify ecological areas, and determine the optimal locations and sample size for monitoring malaria vectors.?

In coastal Kenya, this approach was successful in pinpointing very specific regions with high densities of An. funestus and An. gambiae. Similarly, in Benin, this sampling framework resulted in greater collections of An. gambiae with a reduced number of sample sites – pointing to improved cost-effectiveness.?

Further investigations of mosquitoes gathered through these comprehensive sampling methods are needed to concretely shed light on whether the dynamics of malaria transmission are shifting from indoors to outdoors, and elucidate on concerning aspects such as geographic establishment of An. stephensi. Additional understanding could be gained by combining multiple approaches, such as that described by Bertozzi-Villa and colleagues for clustering malaria transmission settings into archetypes, and an updated version of the 2012 vector map that is being developed by the Vector Atlas team to predict the distribution of malaria vector species. The Vector Atlas also includes the dimension of insecticide resistance, taken from the IR Mapper tool that my company Vestergaard maintains in partnership with KEMRI.?

My view is that rigorous sampling techniques in malaria vector surveillance must be adopted so that we can accurately assess the evolving dynamics of malaria transmission and enhance our vector control strategies. To those of us working in malaria, elimination can sometimes feel very far away. But getting progress back on track starts by ensuring we have a full, evidence-based understanding of the vectors that transmit it.?