Creating mosquito-free outdoor spaces using transfluthrin-treated chairs and ribbons

Abstract

Background Residents of malaria-endemic communities spend several hours outdoors performing different activities, e.g. cooking, story-telling or eating, thereby exposing themselves to potentially-infectious mosquitoes. This compromises effectiveness of indoor interventions, notably long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). This study characterized common peri-domestic spaces in rural south-eastern Tanzania, and assessed protective efficacies of hessian fabric mats and ribbons treated with the spatial repellent, transfluthrin and respectively fitted to chairs and outdoor kitchens, against mosquitoes.Methods Two hundred households were surveyed, and their most-used peri-domestic spaces physically characterized. Protective efficacies of locally-made transfluthrin-emanating chairs and hessian ribbons were tested in outdoor environments of eight households using volunteer-occupied exposure-free double net traps. CDC light traps were used to estimate host-seeking mosquito densities within open-structure outdoor kitchens. Field-collected Anopheles arabiensis and Anopheles funestus mosquitoes were exposed underneath the chairs to estimate 24h-mortality. Finally, WHO insecticide susceptibility tests were conducted on wild-caught Anopheles from the villages.Results Approximately half (52%) of houses had verandas. Aside from these verandas, most houses also had peri-domestic spaces where residents stayed most times (67% of houses with verandas and 94% of non-veranda houses). Two-thirds of these spaces were sited under trees, and only one third (34.4%) were built-up. The outdoor structures were usually makeshift kitchens having roofs and partial walls. Transfluthrin-treated chairs reduced outdoor-biting An. arabiensis densities by 70-76% while transfluthrin-treated hessian ribbons fitted to the outdoor kitchens caused 81% reduction in the general peri-domestic area. Almost all the field-collected An. arabiensis (99.4%) and An. funestus (100%) exposed under transfluthrin-treated chairs died. The An. arabiensis were susceptible to non-pyrethroids (pirimiphos methyl & bendiocarb) but resistant to pyrethroids commonly used on LLINs (deltamethrin & permethrin).Conclusion Most houses had actively-used peri-domestic outdoor spaces where exposure to mosquitoes occurred. The transfluthrin-treated chair and ribbons reduced outdoor-biting malaria vectors in these peri-domestic spaces, and also elicited significant mortality among pyrethroid-resistant field-caught malaria vectors. These two new prototype formats for transfluthrin emanators, if developed further, may constitute new options for complementing LLINs and IRS with outdoor protection against malaria and other mosquito-borne pathogens in areas where peri-domestic human activities are common.

Insecticide-treated eave ribbons for malaria vector control in low-income communities

“…There have also been studies evaluating other transfluthrin-treated hessian emanators [ 42 ], chairs [ 45 ], artistic decorations [ 46 ] and sandals [ 47 ]. A combined analysis of these early studies shows that the transfluthrin-treated hessian products could: (i) retain protective efficacy for 6 months or more [ 42 ], (ii) be readily acceptable to local communities [ 39 , 46 ], (iii) be made locally without specialized skills needed, (iv) offer protection against indoor and outdoor mosquito bites [ 37 , 43 ], (v) have mosquitocidal effects [toxicity] in addition to repellency [ 48 ], and (vi) protect against multiple mosquito species including pyrethroid-resistant Anopheles [ 45 ]. The studies also showed that when used together with traps in push-pull systems, the protective benefit came primarily from the treated eave ribbons themselves [ 44 ].…”

“…funestus mosquitoes which are known to be resistant to pyrethroids. Hence eave ribbons have potential in managing insecticide resistance Masalu et al [ 45 ] 10 Predicting the impact of outdoor vector control interventions on malaria transmission intensity from semi-field studies Statistical modelling of semi field eave ribbons data from Tanzania and Kenya Laboratory-reared Anopheles arabiensis 41–96% Transfluthrin treated eave ribbons provide both personal and community protection. Denz et al [ 49 ] 11 Transfluthrin Eave-Positioned Targeted Insecticide (EPTI) Reduces Human Landing Rate of Pyrethroid Resistant and Susceptible Malaria Vectors in a Semi Field Simulated Peri-domestic Space Eave ribbons were treated following the procedures described by Mmbando et al [ 37 ] Laboratory-reared Anopheles arabiensis 80% 68% Transfluthrin treated eave ribbons have potential tackle the challenges of insecticide resistance in malaria vectors Tambwe et al [ 56 ] 12 Evaluating putative repellent ‘push’ and attractive ‘pull’ components for manipulating the odour orientation of host-seeking malaria vectors in the peri-domestic space Hessian strip [21 m × 0.05 cm] impregnated with 10 ml technical grade transfluthrin prepared in soapy water; the strips suspended overnight indoors to dry Tests were done in large semi-field cage Laboratory-reared Anopheles arabiensis Not assessed 94% Transfluthrin treated hessian fabric strips around eave gaps provide significant protection from mosquito bites in the peri-domestic spaces.…”

“…arabiensis and An. funestus exposed under transfluthrin-treated chairs [ 45 ]. Future research should investigate the functional efficacy of transfluthrin used alone or in combination with other pesticides in areas with confirmed resistance to other pyrethroids commonly used in public health.…”

“…This may include vapour-phase insecticides such as transfluthrin which is currently used in most applications, or contact insecticides to ensure that mosquitoes attempting to enter houses via eaves can be directly killed or incapacitated. Using insecticides with toxicant and repellent effects also reduces the likelihood that mosquitoes are diverted to non-users [ 43 , 45 ]. This way, even non user households can accrue significant communal protection, resulting from the mass killing effects of the product in the user households [ 40 ].…”

Impact of seasonality and malaria control interventions on Anopheles density and species composition from three areas of Uganda with differing malaria endemicity.

“…arabiensis poses a challenge to malaria vector control. Larval source management with microbial larvicides combined with LLINs has been shown to be protective against malaria infections in rural Kenya [69], and there are several measures including treating cattle with insecticide [60], use of odor-baited traps dispensing spatial repellents [70], and trans uthrin-treated chairs and ribbons [71], which could be deployed as control interventions in the future. In Uganda, there is still an information gap regarding the zoophilic behavior of An.…”