Introduction

Malaria vector control has been a major tool for malaria cases control through use of long lasting insecticidal nets (LLINs) and indoor residual spray (IRS) programs (Hamainza et al., 2016).  Although malaria decline is reported throughout endemic areas, residual malaria transmission stills a problem (Tusting et al., 2016; Walker et al., 2016). Residual malaria control needs more tools than, ITN and IRS alone. The use of mosquito repellent can be considered for the protection of residual malaria control (Sangoro et al., 2014; Mng'ong'o et al., 2011). In history, malaria vector – human contact has been used to control disease vector traditionally, either by burning whole plants (Kweka et al., 2008a) or by hanging the plants indoors (Seyoum et al., 2002; Hassanali et al., 2002; Seyoum et al., 2003). In advancement of science and technology, extraction and isolation of active repellent compounds of the plant material has been achieved and evaluated against disease vectors (Mukandiwa et al., 2016; Paluch et al., 2009; Chauhan et al., 2005).  Different plant based repellent have shown the protection efficiency of six to eight hours (Sanghong et al., 2015; Champakaew et al., 2015). The protection efficiency shown by these plants based repellents are similar to what observed with N,N-diethyl-meta-toluamide (DEET), a gold standard known repellent which have offered a protection of up to 8 hours since its inception in 1954 (Gupta et al., 1987).  The short comings of these topical repellents are skin irritations (Shutty et al., 2013) and inconsistent application of the person (Antwi et al., 2008). Due to existence of residual malaria transmission, the sensitive and reliable tools should be in place for better protection which does not need frequent reapplications. The uses of mosquito coils for repelling vectors have found to be efficient for 6 – 8 hours (Msangi et al., 2010). This is only efficient to protect during the first biting cycle of the principal malaria vectors (6-10pm) and expose the person to mosquito bites after 6-8 hours (Msangi et al., 2010).

At the moment different mats with different active ingredients such as allethrin and bioallethrin have been evaluated and proved to have protective efficacy against different species of disease caring biting mosquitoes (Dua et al., 2005; Amalraj et al., 1996; Amalraj et al., 1992). The efficacy was against strains of Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi (Amalraj et al., 1996).

The essence of this trial was to evaluate Risasi, an electric mosquito mat repellent protection efficiency against free fly An. gambiae s.l.. The elective mosquito mat (EMM), the active ingredient is prallethrin, 18mg/mat which is 12% of net content (150mg/mat) of chemical ingredients. These EMM are proposed to be protective for 10 hours.

1 Materials and Methods

1.1 Material evaluated and procedure

Material evaluated was Risasi (Electric mosquito mat (EMM)) which is pyrethroid based repellent. Its active ingredient is prallethrin (18mg/mat) which is intended for 10 hours protections against biting mosquitoes. These mats were manufactured on 5^th April, 2016 and expected to expire on 4^th, April 2019 with a batch No. RMM01.

1.2 Experimental design

The use of human as a subject in evaluation of repellents is regarded an ethical (Kilama, 2010). The better method have to be designed for the evaluation of repellents using mosquitoes behaviors response different studies, a worn sock for 8 – 10 hours has been validated to attract An. gambiae s s.l. as good as a whole human body (Mukabana et al., 2012). A nylon socks were used for collecting whole human odour daily by been worn for 10 hours. This study had 3 arm assessing sampling efficiency of trap in different treatments and designs; (i) validation of worn sock alone against positive control (DEET) efficiency (ii) validation of worn sock alone against MEM  and, (iii) evaluation of the MEM, DEET and worn sock in the same time. The details of each experimental set up are described below.

1.3 Validation of worn sock alone against DEET (Positive control)

A pair of worn sock was obtained from a volunteer who worn them for 10 hours (8:00 to 18:00hrs). One sock was treated with DEET (composition of 20% DEET) spray (positive control) and other was left with worn sock alone (control). Each sock was placed in a CDC-light trap with minor modifications (the bulb was removed from the CDC-light trap to ensure that no light only a worn sock alone or a worn sock with repellent which monitored for effect of response for number of mosquitoes sampled per night. The room used for this evaluation had a size of 5 meters length by 5 meters width. Light traps were switched on after been loaded with worn sock and worn sock sprayed with DEET. The traps operated 30 minutes before the release of 200 unfed females of An. gambiae s.s., 3 days old. Trapped mosquito collection was done in hourly interval by 3 technicians. Each worked for four hours. Mosquito were kept in a paper cup well labeled for each hour and trap treatment. Treatment and control positions were rotated to avoid positional biasness. The experiment lasted for eight (8) days.

1.4 Validation of worn sock alone against mosquito electric mat (MEM)

The protocol was similar to section (i) above, except that the EMM was connected to power and switched on 30 minutes before mosquito release in the room. Traps with worn sock alone and the other with worn sock attached with EMM. Traps rotated positions to avoid positional effect on mosquito responses. The experiment lasted for eight (8) days.

1.5 Evaluation of three treatments at once

In the same room as described in (i) and (ii) above. The points were marked, (East, West, South) these traps with different treatments rotated in each point for 9 days (Latin square of 3x3) days. This rotation eliminated the positional effect. The rest of the procedures remained as (i) and (ii) above.

1.6 Data analysis

Data analysis was performed using GLM univariate analysis in which An. gambiae trapped were considered as dependant variable while days of experiments considered as random effect, treatment time was considered as fixed variable. Programme used for data Analysis was SPSS version 17 while significance level was considered below 5%.

2 Result

2.1 Comparison of trapping efficiency between a trap with worn sock alone with a trap with worn sock sprayed with DEET

The output of GLM univariate analysis showed that, trap location had no effect on sampling efficiency (F = 0.001, df = 2, P=1.000). Experimental days had no any random effect on sampling (F=1.278, df = 7, P=0.266). The treatments used in traps found that, the trap with work alone had higher number of mosquitoes trapped than in a trap with sock sprayed with DEET (df = 1 F= 424.36, P<0.001)(Figure 1).

2.2 Risasi electric mosquito mat (EMM) against worn sock alone

The number of mosquitoes collected in a trap with worn sock alone was statistically higher than those in a trap attached to Risasi Electric mosquito mat slowly releasing prallethrin (F=256.25, df=1, P>0.001) (Figure 2). Position of the trap did not influence the differences on mosquito collection (F=0.434, P=0.511).

The results of long term bioassay with Cx. vishnui group as prey and A.sardea as predator are presented in Table II. The rates of predation of A. sardea during the course of long-term experiments remained almost similar during the entire set of experiments as expressed in terms of clearance rates, which reflected the ability of the predators to regulate the mosquito larvae in real time situations.

2.3 Comparison of three traps at a time

Comparison of three treatments; a trap with a worn sock alone, another with DEET sprayed on worn sock and other with worn sock attached to Risasi electric mosquito mat slowly releasing prallethrin found have a significant variation in mosquito sampling with a trap attached with Risasi electric mosquito mat had least number of mosquito per right (F=353.78, df=2, P>0.001) (Figure 3). The position of any trap had no influence on the number of mosquitoes sampled per right (F=0.319, DF=2, P=0.727). The mean number of mosquitoes sampled hourly was lowest in mosquito electric mat than the rest (Figure 4).

3 Discussions

The findings of the trial have revealed that, the protection efficiency of the slow release Mosquito electric mat, with prallethrin (a synthetic pyrethroid) as active ingredient was 10 hours as indicated by manufacturer. These findings have exceeded the normal 6 hours shown by most topical repellants and coils used (Kweka et al., 2008b; Kweka et al., 2012). The standard topical repellant, DEET had shown to have protective efficacy of 8 hours (Kweka et al., 2008b), but could not reach 10 hours as slow release Mosquito electric mat.  These findings are similar to what was found by previous studies using slow release techniques with synthetic pyrethroid as an active ingredient (Amalraj et al., 1996; Amalraj et al., 1992).

The use of slow released repellent can be of great use against mosquitoes for the control of residual malaria transmission. The slow release containing prallethrin as active ingredient have inhibited anthropophilic malaria vectors for the longer than transfluthrin which was formerly used and another mosquito coils (Msangi et al., 2010). The slow release of prallethrin has shown a great achievement which can be useful in urban and rural areas where electricity is available. The slowly released prallethrin has shown a great efficiency to interrupt both early and late biting cycles of host seeking mosquitoes. This is an achievement which could control well a residual malaria transmission for those who will get out of the nest earlier in the morning and retire late in the evening. It is powerful tool to be used in indoor, enclosed outdoor environment such as night clubs, bars and pubs.

The wide coverage of LLINs and IRS program  have let to reduced biting rates indoor but enclosed areas outdoor experienced increased biting rates(Charlwood et al., 2016; Maia et al., 2016). The emerging of long lasting repellent with pyrethroid as active ingredient have led to a relief for outdoor population before retiring to their beds with LLINs.

4 Conclusion

The findings of this trial have shown extended protection efficiency if only used in enclosed areas where wind should not be blowing fast such as in open spaces. This efficacy has promising results to protect people and reduce or control residual malaria transmission.

Authors’ contribution

EJK designed the experiments and wrote the first draft of the manuscript and data analysis. Edited and reviewed the MS and agreed upon submission.

Acknowledgements

Authors wish to thank Adrian Massawe, Jamima Hamisy and Ibrahim Sungi for experiment set up and data recording. TPRI for provision of infrastructure to conduct the study. There was no financial assistance for this study.

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