Preferred resting surfaces of dominant malaria vectors inside different house types in rural south-eastern Tanzania

Abstract

Background Malaria control in Africa relies extensively on indoor residual spraying (IRS) and insecticide-treated nets (ITNs). IRS typically targets mosquitoes resting on walls, and in few cases, roofs and ceilings, using contact insecticides. Unfortunately, little attention is paid to where malaria vectors actually rest indoors, and how such knowledge could be used to improve IRS. This study investigated preferred resting surfaces of two major malaria vectors, Anopheles funestus and Anopheles arabiensis , inside four common house types in rural south-eastern Tanzania.Methodology The assessment was done inside 80 houses including: 20 with thatched roofs and mud walls, 20 with thatched roofs and un-plastered brick walls, 20 with metal roofs and un-plastered brick walls, and 20 with metal roofs and plastered brick walls, across four villages. In each house, resting mosquitoes were sampled in mornings (6am-8am), evenings (6pm-8pm) and at night (11pm-12.00am) using Prokopack aspirators from multiple surfaces (walls, undersides of roofs, floors, furniture, utensils, clothing, curtains and bed nets).Results Overall, only 26% of An. funestus and 18% of An. arabiensis were found on walls. In grass-thatched houses, 33-55% of An. funestus and 43-50% of An. arabiensis rested under roofs, while in metal-roofed houses, only 16-20% of An. funestus and 8-30% of An. arabiensis rested under roofs. Considering all data together, approximately 40% of mosquitoes rested on surfaces not typically targeted by IRS, i.e. floors, furniture, utensils, clothing and bed nets. These proportions were particularly high in metal-roofed houses (47-53% of An. funestus ; 60-66% of An. arabiensis ).Conclusion While IRS typically uses contact insecticides to target adult mosquitoes on walls, and occasionally roofs and ceilings, significant proportions of vectors rest on surfaces not usually sprayed. This gap exceeds one-third of malaria mosquitoes in grass-thatched houses, and can reach two-thirds in metal-roofed houses. Where field operations exclude roofs during IRS, the gaps can be much greater. In conclusion, there is need for locally-obtained data on mosquito resting behaviours and how these influence the overall impact and costs of IRS. This study also emphasizes the need for alternative approaches, e.g. house screening, which broadly tackle mosquitoes beyond areas reachable by IRS and ITNs.

Wild populations of malaria vectors can mate both inside and outside human dwellings

“…arabiensis showed a preference for less improved houses, such as those with thatched roofs, compared to more improved houses, such as those with metal roofs. Similar preferences have been demonstrated in Anopheles females in several studies [49,58,59]. One clear implication of this observation is that indoor interventions that typically target host-seeking female mosquitoes, such as indoor residual spraying (IRS) [15], may also impact males, possibly explaining why IRS campaigns have been particularly effective against An.…”

“…Inside the houses, mosquitoes were collected from all potential resting surfaces using Prokopack aspirators (John W. Hock Company, Gainesville, FL, USA) to obtain total numbers of mosquitoes resting inside each house. Initially, mosquito collections were conducted only in the morning, separated into early morning (7-9 a.m.) and late morning (9-12 a.m.) collections, but additional collections were subsequently performed in the early evening (6-20 p.m.) and late at night (12 midnight-2 a.m.), as previously described by Msugupakulya et al [49].…”

Influence of Indoor Residual Spay on An. Gambiae S.L. and An. Funestus Abundance, Resting Behavior and Community Perception on Irs Intervention In Kagera-Tanzania

“…One member from Missenyi stated that, "Inside the houses they like to hide behind doors, in bed rooms, and in dark places like under beds but they fear the kitchen because of smoke". These findings are in line with the previous finding conducted in southeastern Tanzania [59]. Community awareness on these sites is a stepping stone towards influencing practices such as environmental cleaning like pruning of banana and coffee trees, slashing of grasses near houses, clearing of stagnant water in compounds especially during the rainy season when breeding sites are many.…”

Using Bayesian state-space models to understand the population dynamics of the dominant malaria vector, Anopheles funestus in rural Tanzania

“…To account for these biases in sampling, we added a new parameter of "trap-biasness" 𝜔 in the observation model for both precision 𝜏 and varying daily means ā 𝜂 . The prior values for 𝜔 were estimated from independent studies from the same locations [6,58], and ranged from 0.05-0.15 (Table 1), with variations between the two life stages 𝜂. Therefore, the observation model for blood-fed and gravid (𝐴 𝜂 )…”