Treated eave screens in combination with screened doors and windows, are more effective than untreated eave screens in a similar combination in reducing indoor and outdoor Anopheles populations under semi-filed conditions in western Kenya

IntroductionHuman habitats remain the main point of human-vector interaction leading to malaria transmission despite sustained use of insecticide treated nets (ITNs) and indoor residual spraying (IRS). Simple structural modifications involving screening of doors, windows and eaves have great potential for reducing indoor entry of mosquitoes and hence malaria transmission. MethodsFour huts, each constructed inside a semi-field structure, allowing the experimental release of mosquitoes at the Kenya Medical Research Institute (KEMRI), Kisumu research station were used in the study. Two huts had untreated eave and door screens and screened air cavities in place of windows in experiment 1 with the eave screen treated using Actellic(R) insecticide in experiment 2. The other two huts remained unscreened throughout the study. First filial (F1) generation of Anopheles funestus from Siaya, F0 reared from An. arabiensis larvae collected from Ahero and An. arabiensis Dongola strain from the insectary were raised to 3-day old adults and used in experiments. Two hundred, 3-day old adults of each species were released in each semi-field structure at dusk and recaptured the following day at 0700hrs and at 0900 hours. A single volunteer slept in each hut under untreated bed net each night of the study. Recaptured mosquitoes were counted and recorded by collection location, either indoor or outdoor of each hut in the different semi-field structures. ResultsSignificantly fewer An. arabiensis from Ahero [RR=0.10; (95%CI: 0.02-0.63); P<0.0145], An. arabiensis Dongola strain [RR=0.11; (95%CI: 0.04 - 0.19); P<0.0001 and An. funestus from Siaya [RR=0.10; (95%CI: 0.06-0.17); P<0.0001] were observed inside modified huts compared to unmodified ones. Treating of eave screen material with Actellic(R) 300CS significantly reduced the numbers An. arabiensis from Ahero [RR=0.003; (95%CI: 0.00-0.03); P<0.0001] and An. arabiensis Dongola strain [RR=0.03; (95%CI: 0.02-0.05); P<0.0001] indoors of huts with treated eave screen compared to huts with untreated eave screens, while totally preventing entry of An. funestus indoors. These modifications cost <250usd/structure. Discussion and ConclusionThis article describes affordable and effective ways of reducing mosquito entry into the house by modifying the eaves, doors and windows. These modifications were highly effective in reducing indoor entry of mosquitoes. Additionally, treatment of eave screen material with an effective insecticide further reduces the Anopheles population in and around the screened huts under semi-field conditions and could greatly complement existing vector control efforts.