Date Published: December 18, 2014
Publisher: Public Library of Science
Author(s): Karel Van Roey, Mao Sokny, Leen Denis, Nick Van den Broeck, Somony Heng, Sovannaroth Siv, Vincent Sluydts, Tho Sochantha, Marc Coosemans, Lies Durnez, Leslie Vosshall. http://doi.org/10.1371/journal.pntd.0003326
Abstract: Scaling up of insecticide treated nets has contributed to a substantial malaria decline. However, some malaria vectors, and most arbovirus vectors, bite outdoors and in the early evening. Therefore, topically applied insect repellents may provide crucial additional protection against mosquito-borne pathogens. Among topical repellents, DEET is the most commonly used, followed by others such as picaridin. The protective efficacy of two formulated picaridin repellents against mosquito bites, including arbovirus and malaria vectors, was evaluated in a field study in Cambodia. Over a period of two years, human landing collections were performed on repellent treated persons, with rotation to account for the effect of collection place, time and individual collector. Based on a total of 4996 mosquitoes collected on negative control persons, the overall five hour protection rate was 97.4% [95%CI: 97.1–97.8%], not decreasing over time. Picaridin 20% performed equally well as DEET 20% and better than picaridin 10%. Repellents performed better against Mansonia and Culex spp. as compared to aedines and anophelines. A lower performance was observed against Aedes albopictus as compared to Aedes aegypti, and against Anopheles barbirostris as compared to several vector species. Parity rates were higher in vectors collected on repellent treated person as compared to control persons. As such, field evaluation shows that repellents can provide additional personal protection against early and outdoor biting malaria and arbovirus vectors, with excellent protection up to five hours after application. The heterogeneity in repellent sensitivity between mosquito genera and vector species could however impact the efficacy of repellents in public health programs. Considering its excellent performance and potential to protect against early and outdoor biting vectors, as well as its higher acceptability as compared to DEET, picaridin is an appropriate product to evaluate the epidemiological impact of large scale use of topical repellents on arthropod borne diseases.
Partial Text: Vector-borne diseases remain major contributors to the burden of diseases in the tropics , . The most important vectors for transmission of diseases are bloodsucking arthropods, and especially mosquitoes. Worldwide, about 3500 mosquito species have been described, but only a few of them are able to transmit human disease. The mosquito-borne diseases of public health importance include malaria, filariasis, and arboviral diseases such as dengue, chikungunya, Japanese encephalitis, and yellow fever , . For these diseases, targeting the mosquito instead of the pathogen contributes greatly to disease prevention. Current vector control programs are primarily based on insecticides , . For malaria, which is one of the most serious vector-borne diseases affecting millions of people, upscaling of vector control programs has greatly contributed to its worldwide decrease, and especially in Southeast Asia substantial progresses have been observed . The present vector control programs are primarily based on the distribution of long-lasting insecticidal nets (LLINs) and/or application of indoor residual spraying (IRS). However IRS has little impact on outdoor resting vectors, and outdoor and/or early biting species are not affected by LLINs . Some vector species, such as Anopheles arabiensis in Africa , Anopheles maculatus and Anopheles dirus in Asia , , or Aedes aegypti and Aedes albopictus are then less or not vulnerable to one of these two preventive methods. As such, in Southeast Asia, residual malaria transmission due to outdoor and early biting malaria vectors constitutes an important, but often neglected, public health concern in some provinces of each country . Vector control is also of high importance in preventing arboviruses such as dengue (Flaviviridae) and chikungunya (Togaviridae) as no treatment or vaccine is available –. However, both viruses are transmitted by the day-and outdoor-biting mosquitoes Ae. aegypti and Ae. albopictus, . As early and outdoor biting proportions of vectors will maintain malaria and arbovirus transmission, there is an urgent need for additional control measures tackling these fractions of the vector population . Synthetic repellents are a common means of personal protection against mosquito bites. N, N-diethyl-3-methylbenzamide (DEET) is the most commonly used active ingredient in commercially available repellents and has gained wide acceptance in the western world . Another promising synthetic repellent, which was developed by Bayer in the 1980s using molecular modelling, is 1-piperidinecarboxylic acid, 2-(2-hydroxyethyl)-,1-methylpropylester (commonly known as picaridin). In contrast to DEET, picaridin does not dissolve plastics and other synthetics (coatings, sealants), and is biodegradable. Moreover it is cosmetically more acceptable (skin feeling, odour) than DEET [in 14]. The effectiveness of this repellents has shown to equal DEET –, or be better than DEET .
The present study is to our knowledge the most extensive study in Southeast Asia that measures the performance of picaridin repellents on wild anopheline and aedine vectors of malaria and arboviruses. The study was designed to measure the performance of the repellents over a five hour window only, as it was part of a project that measures the epidemiological impact of repellent use on malaria and arboviruses, additional to the use of ITNs. As such, it is important that the current gap in protection  due to early and outdoor biting vectors is filled.