Do Topical Repellents Divert Mosquitoes Within a\ud Community?

Repellents are compounds which interfere with the mosquito’s olfactory system hindering them to identify their hosts and succeeding in taking a blood-meal [1]. However, repellents do not eliminate the host-seeking mosquitoes, they simply reduce human-vector contact. Consequently, there is a possibility that individuals, who do not use repellents, experience more bites than usual because mosquitoes are diverted from the repellent users. The objective of this study was to measure if diversion occurs from households that use repellents to those that don’t within a community with incomplete topical repellent coverag An interventional study was performed in three villages of southern Tanzania using 15%-DEET (N,N-Diethyl-meta-toluamide) and a placebo lotion. Three coverage scenarios were investigated: complete repellent coverage (all households were given 15%-DEET), incomplete repellent coverage (80% of households were given DEET-15% and 20% were given a placebo lotion) and no repellent coverage (all households were given a placebo lotion). The coverage scenarios were rotated between villages. Mosquito densities were measured through aspiration of indoor and outdoor resting mosquitoes respective to each enrolled household. Data was analysed using mixed-effects models and the no coverage scenario was used as reference. Placebo users living in a village where 80% of the households used 15%-DEET were likely to have nearly three times more mosquitoes (p<0.001) resting in their dwellings in comparison to households in a village where nobody uses repellent (Table 1) There is strong evidence that mosquitoes are diverted between households that use repellent to those that don’t. This study arises questions on health equity associated with repellent usage. Policy makers should take into consideration these results while devising vector control programs, as less privileged individuals are likely to suffer more mosquito bites and therewith be more exposed to vector-borne diseases if universal coverage is not reached

Do topical repellents divert mosquitoes within a community? Health equity implications of topical repellents as a mosquito bite prevention tool.

OBJECTIVES: Repellents do not kill mosquitoes--they simply reduce human-vector contact. Thus it is possible that individuals who do not use repellents but dwell close to repellent users experience more bites than otherwise. The objective of this study was to measure if diversion occurs from households that use repellents to those that do not use repellents. METHODS: The study was performed in three Tanzanian villages using 15%-DEET and placebo lotions. All households were given LLINs. Three coverage scenarios were investigated: complete coverage (all households were given 15%-DEET), incomplete coverage (80% of households were given 15%-DEET and 20% placebo) and no coverage (all households were given placebo). A crossover study design was used and coverage scenarios were rotated weekly over a period of ten weeks. The placebo lotion was randomly allocated to households in the incomplete coverage scenario. The level of compliance was reported to be close to 100%. Mosquito densities were measured through aspiration of resting mosquitoes. Data were analysed using negative binomial regression models. FINDINGS: Repellent-users had consistently fewer mosquitoes in their dwellings. In villages where everybody had been given 15%-DEET, resting mosquito densities were fewer than half that of households in the no coverage scenario (Incidence Rate Ratio [IRR]=0.39 (95% confidence interval [CI]: 0.25-0.60); p<0.001). Placebo-users living in a village where 80% of the households used 15%-DEET were likely to have over four-times more mosquitoes (IRR=4.17; 95% CI: 3.08-5.65; p<0.001) resting in their dwellings in comparison to households in a village where nobody uses repellent. CONCLUSIONS: There is evidence that high coverage of repellent use could significantly reduce man-vector contact but with incomplete coverage evidence suggests that mosquitoes are diverted from households that use repellent to those that do not. Therefore, if repellents are to be considered for vector control, strategies to maximise coverage are required

Mosquito collection sites and some households of the Mbingu area, Kilombero Valley, Tanzania.

<p>A – Household made with thatch wall and thatch roof with a blue barrel and a car tyre serving as artificial resting places. B – Household made with brick walls and thatch roof, the artificial resting places are not visible because they were deployed behind the household. C – Household made of mud walls and thatch roof with a blue barrel and a car tyre serving as artificial resting places. D – <i>Kibanda</i>, outdoor kitchen area.</p