Screening mosquito entry points into houses with novel long-lasting insecticidal netting to reduce indoor vector densities and mitigate pyrethroid-resistance
Centro de Investigação em Saúde de Manhiça Bairro Cambeve, Rua 12, Distrito da Manhiça CP 1929, Maputo, Moçambique
Barcelona Institute for Global Health (ISGlobal), Carrer del Rosselló 132 - planta 6, 08036 Barcelona, Spain
2. Lauren Cator
Imperial College London, Department of Life Sciences, Silwood Park Campus, Ascot SL57PY UK
3. Neil Lobo
University of Notre Dame, Galvin Life Sciences, Notre Dame, IN 46556, USA
Long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) have tremendously reduced malaria infection prevalence in endemic Africa. These tools remain the cornerstones in malaria control and elimination efforts, but are failing in many malarious areas due to insecticide resistance and residual malaria transmission. To sustain the gains in malaria control and elimination, alternative vector control tools are urgently needed. Housing improvement has been shown to reduce and prevent human-vector contacts inside human dwellings. However, while proven effective, this intervention remains underused in lower middle income countries. It may be a tool for sustainable malaria control in southern Mozambique, where -despite universal LLINs and IRS coverage - Anopheles funestus and An. arabiensis remain important vectors sustaining indoor transmission. The proposed proof-of-principle study in this area aims to address this protective gap of LLINs and IRS by evaluating the impact of housing improvement on indoor biting malaria vectors. In an experimental hut study, preferred points of house entry will be investigated to determine if mosquito vectors enter houses through openings at ground level (under doors), roof level (through the eaves) or intermediate level (via windows). This is assessed by counting mosquitoes that enter so-called mosquito entry traps, which are installed behind each of these openings. These traps capture host-seeking mosquitoes that are attracted by a study volunteer sleeping inside the hut under a LLIN. In a different study, mosquito entry points (windows and eaves) will be left unscreened in one hut, whereas the windows and eaves in two other huts will be screened with a novel durable polymer netting that is either untreated in one hut or chlorfenapyr-treated in the other. To evaluate whether the experimental huts differ in indoor mosquito densities overnight, host-seeking mosquitoes will be collected with standard mosquito traps inside the huts. Again, mosquitoes are attracted by study volunteers who sleep inside the huts under LLINs. Chlorfenapyr-treated mesh is selected as it could have a direct advantage over untreated mesh by killing host-seeking mosquitoes contacting the mesh. As chlorfenapyr has the potential to control the local pyrethroid-resistant mosquitoes, live mosquitoes will be collected indoors and mortality will be followed daily for up to 5 days. If increased (delayed) mortality is observed, house improvements with insecticide-treated mesh may become part of the resistance management toolbox to tackle the insecticide resistance problem in southern Mozambique.
Finally, the effect of sunlight, UV, wind and rain on the biological activity of the chlorfenapyr-treated mesh is monitored throughout the trial through standard cone bio-assays assessing mosquito mortality on the mesh. This is of importance as window screens may be exposed to similar weather conditions for at least part of the day.
The obtained baseline data will require immediate evaluation towards evidence-based decision making. The project is timely as Mozambique is drafting its malaria elimination strategic plan but entomological intelligence highlights that additional tool (to current LLINS and IRS) are urgently needed to sustain the gains in malaria control.