On-going Research & Development
Development of an Affordable Indoor and Outdoor mosquito Repellent Clothing technology
Study Title: Laboratory evaluation of Repellent Clothing against laboratory and wild reared Anopheles gambiae, Culex quinquefasciatus and Aedes aegypti mosquitoes in Tanzania
Investigators: Gilbert Abel Munishi & Yeromin Paul Mlacha (PhD)
Introduction
Many African countries have experienced some outbreaks of mosquito-borne pathogens and arboviruses diseases such as malaria, dengue, chikungunya, rift valley fever, yellow fever and zika virus which have consumed a lot of lives. These diseases accounts for 17% of the global burden of communicable diseases. In Tanzania, 93% of the population live in areas where malaria transmitted. Since 2014 Tanzania has experienced several dengue outbreaks especially in the city of Dar es salaam and Tanga. Long lasting insecticide treated nets (LLINs) and indoor residual spray (IRS) are the primary method of malaria control in Sub-Sahara Africa. LLINs have helped to reduce malaria incidence by 42% and mortality by 66% in Africa in the last 15 years. However, several studies have documented the existence if insecticides resistance among malaria vectors in Tanzania which could jeopardize the existing LLINs and IRS interventions. Alterations in mosquitoes’ behavioural patterns as some preferred to feed earlier and more frequently outdoors than previously observed, increases the contact between mosquitoes and human beings, rendering LLINs and IRS less effective. Some of the mosquito vectors such as Aedes species tends to bite during the day when people are awake and are outside their home.
Additionally, the current interventions of IRS and LLINs may not provide full protection in some humanitarian situations such as in refugee camps, mining, fishing, security guards workers and nomadic populations. Some alternative interventions have been developed such as insecticide treated blankets and uniforms, but its applicability must depend on the weather condition and acceptability. Based on the reported challenges, there is an urgent need to develop new interventions to supplement the current interventions. Therefore, Noobites company has produced a mosquito repellent clothing technology which can be used outdoors and indoors and across various populations. The product is made up from extracts from gum tree (eucalyptus) and lemongrass. Previous studies have documented various uses of extracts from these plants such as ingredients in cosmetics, food preservatives, possesses pharmacological. Lemongrass has a non-toxic mechanism of action and is thought to be safe for both human health and the environment. Lemongrasses are reported to be weak irritant in human skin. Eucalyptus oil poisoning is rare in adults compare to children. The common side effects in children include seizures and vomiting. The Noobites360 product prevents mosquito-borne diseases by initially repelling the mosquitoes and preventing them from blood-feeding on human hosts. However, the technology needs to be tested for its efficacy against various mosquito vectors before becoming available for public use. Therefore, the main objective of the study is to determine the protective efficacy of the washed and unwashed repellent clothing against human-biting mosquitoes.
Study Outcomes
The primary outcome of the study will be landing/probing inhibition (%, 95% CI), percentage (%) 1hr Knock Down, percentage (%) 24-hour Mortality, percentage (%) blood feeding-success. The findings of this study will inform the next research steps which includes semi field, experimental hut and field studies.
Methods
This is a laboratory study to determine the efficacy of NoobitesMRCT treated cloth. Arm-in-cage tests and WHO Cone bioassays will be conducted as per WHO guidelines. WHO Cone bioassays plays an integral role in the evaluation of insecticides used on a variety of treated substrates. Cone bioassays from each of the sampled repellent cloth (washed and unwashed) will be performed. Five pieces of 25 cm x 25 cm size will be cut on each piece sample, standard WHO cone will be placed and held in place using a plastic manifold. Five mosquitoes from each strain will be introduced into each cone and exposed for 3 minutes. After the exposure, the mosquitoes will be removed from the cones and kept separately in paper cups provided with 10% sugar solution. Knockdown will be recorded after one hour and mortality after 24, 48 and 72 hours.
Arm-in-Cage tests are a common way to investigate the efficacy of repellent formulations of topical repellents and impregnated textiles. Twenty (20) volunteers will be enrolled to participate in the study. They will test the treatments sequentially for all three mosquito species. The volunteers will then be randomly assigned one of the twenty 5-wash shirts for testing. This will be repeated for 10, 15 and 20 washes. However, the washes will be extended to 50 washes at interval of five (5) washes to measure the rate of decay of the repellent. Three cages sized 35 - 40 cm per side will be used per replicate. During Arm-in-Cage tests the following procedures will be followed.
1. Three (3) mosquito cages (size: 35–40 cm per side) each containing 200–250 non-blood-fed females will be used. One cage is designated for testing the candidate repellent (Noobites360) and the other two for the positive control (arm with ethanolic deet) and negative control (Untreated cloth). Initially, the readiness of mosquitoes to land and/or probe must be assessed by inserting an untreated cloth arm into a cage for 30 seconds or until 10 landings/probings are counted. The procedure is repeated with the other arm in the second cage and the third cage.
2. Before testing commences, 1 mL of the candidate repellent prepared in alcohol/diluent solution is applied to one arm and 1 mL of the deet standard solution is applied to the other arm. After 30 minutes, the repellent-treated arm is inserted into the appropriate cage and exposed for 3 minutes to determine landing and/or probing activity. Next, the deet-applied arm is exposed to determine landing and/or probing activity. This procedure is repeated at 30- or 60-minute intervals and should be used consistently throughout the experiment.
3. The occurrence of one landing and/or probing in a 3-minute test interval concludes the test for that repellent dose. Complete protection time is calculated as the number of minutes elapsed between the time of repellent application and the first mosquito landing and/or probing. Replicate tests repeat this process using different batches of mosquitoes over several days.
Relevance of the study to the public Health in Tanzania
The study will provide evidence on the efficacy of repellent clothing technology against human-biting mosquitoes vectors. Due to its wide range of applicability, it will also control malaria vectors which bites and rests outdoors such as An. arabiensis and Aedes mosquito which primarily bites during the day and outdoors. Its contribution towards malaria control and eliminations will be assessed in various phases of the study whereby, in the present laboratory phase, the repellent rate among mosquito vectors will be revealed. Therefore, mosquito repellent clothing intervention will complement the existing IRS and LLINs which are the main tools for mosquito control in Africa.