Nigel Hill

Expert Review of the Evidence Base for Arthropod Bite Avoidance

Bite avoidance measures are commonly recommended to international travelers to help reduce the risk of various arthropod‐borne diseases. A key strategy is the use of repellents applied topically to skin or clothing which are considered in the first part of this review. Also advised are a variety of methods that employ the use of insecticides and physical barriers such as mosquito nets or oil preparations applied to the skin. In the following document, the authors considered some of the most widely used bite avoidance methods and identified the strength and quality of evidence that determined efficacy. The overall purpose of the review is to provide the available evidence, in a graded format, upon which to base recommendations for the selection of appropriate repellents and other methods of bite avoidance in those traveling overseas. The authors were asked to consider the effectiveness of the most commonly used active ingredients (AIs) in repellent formulations and methods of bite avoidance. The evidence base considered protection against nuisance biting insects, reduction in the incidence of arthropod‐borne diseases, and safety profile. Effectiveness of the repellent related to spectrum of activity against various mosquito species and other arthropods was examined as well as longevity of applied dose. Where possible, efficacy was compared to deet as being the accepted gold standard. All sections employed MEDLINE via PubMed in literature searches augmented by others depending on the subject area investigated. Details of the review process can be found at http://www.istm.org; click on “ISTM Committees” and then “Publications.” ### Major Findings N , N ‐diethyl‐3‐methylbenzamide (deet), (2‐(2‐hydroxyethyl)‐piperidinecarboxylic acid 1‐methyl ester (icaridin), p ‐methane 3, 8‐diol (PMD), and ethyl butylacetylaminopropionate (IR3535)‐based repellents all provide protection against biting arthropods, but volatile oils and other natural products are less reliable. On the strength of available evidence, the first‐line choice for those visiting areas where …

Amplification and analysis of human DNA present in mosquito bloodmeals

Abstract. DNA fingerprinting should permit the identification of individual human hosts of haematophagous arthropods, providing epidemi‐ologically useful information, for example, the biting rates on different people and the impact of insecticide‐impregnated bednets.

Field Evaluation of Traditionally Used Plant-Based Insect Repellents and Fumigants Against the Malaria Vector Anopheles darlingi in Riberalta, Bolivian Amazon

Abstract Inexpensive insect repellents may be needed to supplement the use of impregnated bed-nets in the Amazon region, where the primary malaria vector, Anopheles darlingi (Root), is exophilic and feeds in the early evening. Three plants that are traditionally used to repel mosquitoes in Riberalta, Bolivian Amazon, were identified by focus group, and then they were tested against An. darlingi as well as Mansonia indubitans (Dyar & Shannon)/Mansonia titillans (Walker). Cymbopogon citratus (Staph), Guatemalan lemongrass, essential oil at 25% was used as a skin repellent, and it provided 74% protection for 2.5 h against predominantly An. darlingi and 95% protection for 2.5 h against Mansonia spp. Attalea princeps (name not verified) husks, burned on charcoal in the traditional way provided 35 and 51% protection against An. darlingi and Mansonia spp., respectively. Kerosene lamps, often used to light rural homes, were used as a heat source to volatilize 100% Mentha arvensis (Malinv ex. Bailey) essential oil, and they reduced biting by 41% inside traditional homes against Mansonia spp., although they were ineffective outdoors against An. darlingi. All three plant-based repellents provided significant protection compared with controls. Plant-based repellents, although less effective than synthetic alternatives, were shown by focus groups to be more culturally acceptable in this setting, in particular para-menthane-3, 8, idol derived from lemon eucalyptus, Corymbia citriodora (Hook). Plant-based repellents have the potential to be produced locally and therefore sold more cheaply than synthetic commercial repellents. Importantly, their low cost may encourage user compliance among indigenous and marginalized populations.

Are mosquitoes diverted from repellent‐using individuals to non‐users? Results of a field study in Bolivia

Outside sub‐Saharan Africa, Anopheline mosquito exophagic and/or crepuscular behaviour patterns imply that insecticide‐treated nets may provide incomplete protection from malaria‐infective mosquito bites. Supplementary repellent treatment has been recommended in such circumstances, especially where vectors are exophilic and so are not susceptible to residual insecticide spraying. As maintaining complete usage of repellents in a community is unrealistic, the potential negative impact on non‐users of repellent usage by ‘neighbours’ in the same community needs to be addressed in the context of health policy promoting equity. This study quantifies diversion of host‐seeking mosquitoes, from repellent wearing to unprotected individuals, 1 m apart under field conditions in Bolivia. Each of the six volunteer‐pairs sat >20 m apart from other pairs. Volunteers were allocated di‐ethyl toluamide (DEET) or mineral oil in ethanol control. Treatments were rotated, so that during the trial, both pair‐members wore repellent on 72 occasions; both pair‐members wore control on 72 occasions; and on 36 occasions, one pair‐member wore repellent and the other control. Unprotected (control) pair‐members received 36.4% [95% confidence interval (CI): 8.1–72.0%] more Anopheles darlingi landings (P = 0.0096) and 20.4% (95% CI: 0.6–44.0%) more mosquito landings (P = 0.044), when their ‘partner’ wore repellent than when their partner also wore control. A second, smaller Latin‐square trial using 30% lemongrass (Cymbopogon citratus) repellent, with control, obtained 26.0% (95% CI: 5.2–51.0%) more mosquito landings when controls sat with repellent‐wearers rather than other controls (P = 0.0159). With incomplete community repellent usage, non‐users could be put at an increased risk of malaria. The results also have implications for repellent‐efficacy assay design, as protection will appear magnified when mosquitoes are given a choice between repellent‐users and non‐users.

Border malaria in China: knowledge and use of personal protection by minority populations and implications for malaria control: a questionnaire-based survey

BackgroundMalaria control in remote, forested areas of the Mekong region relies on personal protection from mosquito bites. Uptake of these methods may be limited by knowledge of the link between mosquitoes and malaria as well as social and economic aspects. Understanding barriers to uptake will inform malaria control programmes on targets for improvement of delivery.MethodsA total 748 key respondents: health providers and village heads, from 187 villages and 25 different ethnic groups, were interviewed using structured questionnaires. Differences in use of personal protection, and knowledge of malaria between groups were analysed using chi-square; and binary logistic regression used for multivariate analysis.ResultsMalaria knowledge was poor with 19.4% of women and 37.5% of men linking mosquitoes with malaria, although 95.6% knew one or more methods of mosquito control. Virtually all respondents used personal protection at some time during the year; and understanding of malaria transmission was strongly associated with bednet use. Those working in forest agriculture were significantly more likely to know that mosquitoes transmit malaria but this did not translate into a significantly greater likelihood of using bednets. Furthermore, use of personal protection while woing outdoors was rare, and less than 3% of respondents knew about the insecticide impregnation of bednets. The use of bednets, synthetic repellents and mosquito coils varied between ethnic groups, but was significantly more frequent among those with higher income, more years of education and permanent housing. The reported use of repellents and coils was also more common among women despite their low knowledge of malaria transmission, and low likelihood of having heard information on malaria within the last year.ConclusionThe use of personal protection must be increased, particularly among outdoor workers that have higher malaria risk. However, personal protection is widely used and widely accepted to prevent nuisance biting mosquitoes, with the major barrier to use being affordability. Therefore, social marketing campaigns aimed at women and those that work outdoors that provide highly subsidised products, especially insecticide impregnation kits for bednets and hammock nets are most likely to succeed in lowering malaria morbidity among non Han-Chinese groups in rural China.

Risk factors for mosquito house entry in the Lao PDR.

Background Construction of the Nam Theun 2 hydroelectric project and flooding of a 450 km2 area of mountain plateau in south-central Lao PDR resulted in the resettlement of 6,300 people to newly built homes. We examined whether new houses would have altered risk of house entry by mosquitoes compared with traditional homes built from poorer construction materials. Methodology/Principal Findings Surveys were carried out in the Nam Theun 2 resettlement area and a nearby traditional rice farming area in 2010. Mosquitoes were sampled in bedrooms using CDC light traps in 96 resettlement houses and 96 traditional houses and potential risk factors for mosquito house entry were recorded. Risk of mosquito house entry was more than twice as high in traditional bamboo houses compared with those newly constructed from wood (Putative Japanese Encephalitis (JE) vector incidence rate ratio (IRR) = 2.26, 95% CI 1.38–3.70, P = 0.001; Anopheline IRR = 2.35, 95% CI: 1.30–4.23, P = 0.005). Anophelines were more common in homes with cattle compared against those without (IRR = 2.32, 95% CI: 1.29–4.17, P = 0.005).Wood smoke from cooking fires located under the house or indoors was found to be protective against house entry by both groups of mosquito, compared with cooking in a separate room beside the house (Putative JE vector IRR = 0.43, 95% CI: 0.26–0.73, P = 0.002; Anopheline IRR = 0.22, 95% CI: 0.10–0.51, P<0.001). Conclusions/Significance Construction of modern wooden homes should help reduce human-mosquito contact in the Lao PDR. Reduced mosquito contact rates could lead to reduced transmission of diseases such as JE and malaria. Cattle ownership was associated with increased anopheline house entry, so zooprophylaxis for malaria control is not recommended in this area. Whilst wood smoke was protective against putative JE vector and anopheline house entry we do not recommend indoor cooking since smoke inhalation can enhance respiratory disease.

A household randomized, controlled trial of the efficacy of 0.03% transfluthrin coils alone and in combination with long-lasting insecticidal nets on the incidence of Plasmodium falciparum and Plasmodium vivax malaria in Western Yunnan Province, China

BackgroundMosquito coils are the most commonly used household insecticidal product in the world with sales exceeding 50 billion coils, used by two billion people worldwide annually. Despite strong evidence that coils prevent mosquito bites a systematic review concluded that there is no evidence that burning mosquito coils prevents malaria acquisition. Therefore, the current trial was designed to measure and compare prevention of malaria infection by mosquito coils or long-lasting insecticidal net (LLIN) or a combination of the two in Yunnan, China in the Greater Mekong sub-region.MethodsA four-arm single blind household-randomized design was chosen as coils emanate insecticide throughout the household. Households enrolled at baseline were randomly allocated by the lottery method to one of the four intervention arms: (i) nothing, (ii) 0.03% transfluthrin coils alone, (iii) deltamethrin long-lasting insecticide treated nets, (LLINs) alone or (iv) a combination of transfluthrin coils and deltamethrin LLINs. All household members were recruited to the study, with only those households excluded with pregnant or breastfeeding mothers, members with chest complaints or allergies or members that regularly slept away from home. The main outcome of interest was Plasmodium falciparum malaria prevalence detected by rapid diagnostic tests (RDTs) during six repeated monthly cross-sectional surveys. The secondary outcome of interest was the effect on Plasmodium vivax prevalence detected in the same way.ResultsA total of 2,052 households were recruited into the study, comprising 7,341 individuals The odds ratios of testing positive by RDT with P. falciparum or P. vivax were >75% lower for all intervention arms compared with the control arm. Coils alone provided 77% protection (95% CI: 50%-89%), LLINs provided 91% protection (95% CI: 72%-97%) and the combination of coils and LLINs provided 94% protection (95% CI: 77%-99%) against P. falciparum compared with the control arm. There was no statistically significant difference between the protective efficacies of the different interventions.ConclusionsThis is the first robust clinical evaluation of transfluthrin mosquito coils as a means to reduce malaria and the high degree of infection prevented would indicate they represent a potentially highly effective tool, which could be integrated into larger vector control programmes.Trial registrationClinicalTrials.gov Identifier:NCT00442442, March 2007.

Risk Factors for the Presence of Aedes aegypti and Aedes albopictus in Domestic Water-Holding Containers in Areas Impacted by the Nam Theun 2 Hydroelectric Project, Laos

We assessed risk factors for vectors of dengue and chikungunya viruses near a new hydroelectric project, Nam Theun 2, in Laos. Immature stages of Aedes aegypti were found only in sites within 40 km of the urban provincial capital, but Aedes albopictus was found throughout. Aedes aegypti pupae were most common in water storage jars (odds ratio [OR] = 4.72) and tires (OR = 2.99), and Ae. albopictus pupae were associated with tires in 2009 (OR = 10.87) and drums, tires, and jars in 2010 (drums OR = 3.05; tires OR = 3.45, jars OR = 6.59). Compared with water storage vessels, containers used for hygiene, cooking, and drinking were 80% less likely to harbor Ae. albopictus pupae in 2010 (OR = 0.20), and discarded waste was associated with a 3.64 increased odds of infestation. Vector control efforts should focus on source reduction of water storage containers, particularly concrete jars and tires.

Permethrin-Impregnated Mattress Liners: a Novel and Effective Intervention Against House Dust Mites (Acari: Pyroglyphididae)

Abstract This study tested the efficacy of permethrin-impregnated mattress liners in reducing house dust mites in the homes of volunteers with no previous recorded history of asthma, atopic eczema, or perennial rhinitis. The field trial using permethrin-impregnated (450 mg/m2 of pure permethrin in polyester netting weighing 35 g/m2) mattress liners (n = 9) was conducted for 27 mo. The permethrin-impregnated bedding significantly reduced house dust mites in mattresses for at least 27 mo. Allergen concentrations were significantly lowered at 15-mo postintervention. No adverse side-effects were reported. This is a promising development in house dust mite control.

Control of head lice: past, present and future.

Pediculosis capitis is common among children. Rapid and accurate detection is an underlying principle of effective control and the use of a fine-tooth comb in wet, conditioned hair is most sensitive. However, none of the available treatments are fully effective. Of the current pediculicides available over the counter in the UK, those based on malathion are more effective than pyrethroids. Carbaryl is likely to be the most effective insecticide but is only available on prescription. Wet combing with conditioner has proven to be as effective as some over-the-counter lotions for unsupervised use in the home. There are several promising candidates for new insecticidal actives that are likely to be highly effective for a new generation of pediculicides, as well as a variety of unconventional novel treatments.