Insecticide Susceptibility of Phlebotomus argentipes in Visceral Leishmaniasis Endemic Districts in India and Nepal

et al. (2010) Insecticide Susceptibility of Phlebotomus argentipes in Visceral Leishmaniasis Endemic Districts in India and Nepal. PLoS Negl Trop Dis 4(10): e859. doi:10.1371/journal.pntd.0000859 Insecticide Susceptibility of Phlebotomus argentipes in Visceral Leishmaniasis Endemic Districts in India and Nepal Diwakar Singh Dinesh 0 Murari Lal Das 0 Albert Picado 0 Lalita Roy 0 Suman Rijal 0 Shri Prakash Singh 0 Pradeep Das 0 Marleen Boelaert 0 Marc Coosemans 0 Shaden Kamhawi, National Institutes of Health, United States of America 0 1 Rajendra Memorial Research Institute of Medical Sciences , Patna , India , 2 B.P. Koirala Institute of Health Sciences , Dharan , Nepal , 3 Institute of Tropical Medicine Antwerp, Antwerp, Belgium, 4 London School of Hygiene and Tropical Medicine , London , United Kingdom , 5 Banaras Hindu University , Varanasi , India Objectives: To investigate the DDT and deltamethrin susceptibility of Phlebotomus argentipes, the vector of Leishmania donovani, responsible for visceral leishmaniasis (VL), in two countries (India and Nepal) with different histories of insecticide exposure. Methods: Standard WHO testing procedures were applied using 4% DDT and 0.05% deltamethrin impregnated papers. The effect of the physiological status (fed and unfed) of females on the outcome of the bioassays was assessed and the optimal time of exposure for deltamethrin was evaluated on a colony population. Field populations from both countries were tested. Results: Fed and unfed females responded in a similar way. For exposure time on field samples 60 min was adopted for both DDT and deltamethrin. In Bihar, knockdown and mortality with DDT was respectively 20 and 43%. In Nepal almost all sand flies were killed, except at the border with Bihar (mortality 62%). With 0.05% deltamethrin, between 96 and 100% of the sand flies were killed in both regions. Conclusions: Based on literature and present data 4% DDT and 0.05% deltamethrin seem to be acceptable discriminating concentrations to separate resistant from susceptible populations. Resistance to DDT was confirmed in Bihar and in a border village of Nepal, but the sand flies were still susceptible in villages more inside Nepal where only synthetic pyrethroids are used for indoor spraying. The low effectiveness of indoor spraying with DDT in Bihar to control VL can be partially explained by this resistance hence other classes of insecticides should be tested. In both countries P. argentipes sand flies were susceptible to deltamethrin. - Funding: The work was financially supported by European Union-funded 6th Framework/INCO-DEV KALANET project (EU contract no 015374). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. . These authors contributed equally to this work. Approximately 200 million people are at risk of visceral leishmaniasis (VL) also known as kala-azar in Bangladesh, India and Nepal [1]. In South East Asia, VL is caused by Leishmania donovani Laveran & Mesnil (Kinetoplastida: Trypanosomatidae) which is transmitted by Phlebotomus argentipes Annandale & Brunneti (Diptera: Psychodidae), the only incriminated vector in the region [2]. VL is fatal if untreated and current control measures rely on diagnosis and treatment of cases and Indoor Residual Spraying (IRS) to reduce or interrupt transmission in the affected communities. In India, two annual rounds of DDT spraying at 1 mg/m2 have been conducted in VL endemic districts since more than two decades [3]. In Nepal, the use of DDT to control VL was stopped in 1995 and IRS has been based since on synthetic pyrethroids (i.e alphacypermethrin or lambdacyhalothrin) targeting communities reporting at least one VL case in the previous year [4]. In Bangladesh vectorcontrol activities are practically inexistent [5]. The use of Long Lasting Insecticidal Nets (LN), deltamethrin, alphacypermethrin or permethrin based [6], have been postulated as an alternative or complimentary approach as the current vector control strategies are failing to control VL in the region [7,8]. Among other reasons, P. argentipes resistance to the insecticides used in the national programs may explain the lack of effect observed, particularly in India and Nepal. In a recent review, Ostyn et al. [8] reviewed the published reports on P. argentipes susceptibility to different insecticides in the Indian subcontinent since 1978. The results of this review show that DDT resistance has been reported in India since early 1990s but the results were variable and patchy. P. argentipes were consistently susceptible to DDT in Nepal and Bangladesh but the number of reports from those two countries was limited. Studies in the region showed susceptibility to deltamethrin, except for a report from Visceral leishmaniasis (VL), also know as kala azar, is one of the major public health concerns India, Nepal and Bangladesh. In the Indian subcontinent, VL is caused by Leishmania donovani which is transmitted by Phlebotomus argentipes. To date, Indoor Residual Spraying (IRS) campaigns have been unable to control the disease. Vector resistance to the insecticides used has been postulated as one of the possible reasons explaining this failure. A number of studies in the region have shown a variable degree of resistance to DDT in areas where this insecticide has been widely used for IRS (mainly India). However there is no coordinated and standardized program to monitor resistance to insecticides in the region. In this study we tested P. argentipes susceptibility to DDT and deltamethrin in VL endemic villages in India and Nepal. The results confirmed the DDT resistance in India and in a border village of Nepal. P. argentipes from both countries were in general susceptible to deltamethrin, an insecticide used in some long lasting insecticidal nets. Pondicherry, India [9]. However the methodologies used in those surveys were not standardized (i.e. insecticide concentration and time of exposure varied) and none of the studies applied the same protocol in different regions simultaneously. In this paper we present the results of two studies on P. argentipes susceptibility to insecticides. First, a laboratory test to asses the influence of the physiological status of the sand fly on insecticide efficacy and to standardize the time of exposure to deltamethrin for field assays. Secondly, a field study was carried out to assess P. argentipes resistance to DDT and deltamethrin in VL endemic villages in India and Nepal. Materials and Methods Ethics statement The protocol study was approved by the ethical review boards from the London School of Hygiene and Tropical Medicine, University of Antwerp, Rajendra Memorial Research Institute and B.P. Koirala Institute of Health Sciences. Written informed consent was obtained from the head of the household where the sand flie (...truncated)