Insecticide susceptibility status of malaria vectors in Himachal Pradesh, India :Gaurav Kumar, VP Ojha, Ramesh C Dhiman, Journal of Vector Borne Diseases

RESEARCH ARTICLE
Year : 2022 | Volume : 59 | Issue : 3 | Page : 236--240

Insecticide susceptibility status of malaria vectors in Himachal Pradesh, India

Gaurav Kumar, VP Ojha, Ramesh C Dhiman
ICMR-National Institute of Malaria Research, Delhi, India

Correspondence Address:
Ramesh C Dhiman
Ramesh C Dhiman, ICMR-National Institute of Malaria Research, Sector-8, Dwarka, Delhi
India

Abstract

Background & objectives: The state of Himachal Pradesh is one of the hilly forested states of India. Warming of climate has been evidenced in the state due to the ongoing climate change which may cause the upsurge/introduction of mosquito-borne diseases. To curb disease transmission, an effective vector control strategy will be required. Methods: Insecticide susceptibility status of available malaria vectors was determined using the standard WHO method in six districts Kangra, Una, Mandi, Bilaspur, Solan and Mandi of the state. An. culicifacies and An. fluviatilis were tested against DDT (4%), malathion (5%) and deltamethrin (0.05%) using WHO insecticide susceptibility kits. Results: Overall, An. culicifacies was found resistant to DDT in all the six districts, susceptible to malathion in all districts except Bilaspur and Solan where it showed possible resistance. It was susceptible to deltamethrin in all the study districts. An. fluviatilis was resistant to DDT and susceptible to malathion and deltamethrin in Kangra and Una districts. Interpretation & conclusion: At present, indoor residual spraying (IRS) is not being undertaken in Himachal Pradesh. However, with the information generated through the present study, the state government can plan evidence-based IRS at least for focal spray in limited foci reporting malaria incidence.

How to cite this article:
Kumar G, Ojha V P, Dhiman RC. Insecticide susceptibility status of malaria vectors in Himachal Pradesh, India.J Vector Borne Dis 2022;59:236-240

How to cite this URL:
Kumar G, Ojha V P, Dhiman RC. Insecticide susceptibility status of malaria vectors in Himachal Pradesh, India. J Vector Borne Dis [serial online] 2022 [cited 2023 Mar 29 ];59:236-240
Available from: http://www.jvbd.org//text.asp?2022/59/3/236/342394

Full Text

INTRODUCTION

Malaria is one of the major vector-borne diseases prevalent in India resulting in nearly one million cases with 194 deaths during 2017[1]. The disease is caused by five species of Plasmodium parasites and transmitted by the infected bite of female Anopheles mosquitoes. There are six primary vectors of malaria in the country, viz., Anopheles culicifacies, An. fluviatilis, An. minimus, An. baimaii, An. stephensi and An. sundaicus. In addition, some species of Anopheles also play a secondary role in specific geographic areas. The National Vector Borne Disease Control Programme (NVBDCP) of India is the nodal agency for formulating guidelines for the control of malaria in the country. Vector control is an important component of malaria control strategy and in rural areas, it is done by indoor residual spray (IRS) with a suitable insecticide, use of long-lasting insecticide nets (LLIN), and larviciding in urban areas. Insecticides of three classes, viz., organochlorine (DDT), organophosphate (malathion), and synthetic pyrethroids (deltamethrin, cyfluthrin, lambdacyhalothrin, bifenthrin, and alphacypermethrin) have been approved by NVBDCP for IRS. Regular exposure of anopheline vectors to these insecticides has resulted in the development of resistance in mosquitoes. Successful control of mosquito population by IRS and/ or LLIN depends on previous knowledge of insecticide susceptibility status of mosquitoes to different categories of insecticides. It is therefore imperative to conduct routine tests for the assessment of insecticide susceptibility status of local malaria vectors for evidence based control strategy.

The state of Himachal Pradesh lies in the western Himalayas and the climate of this region is comparatively cooler than the rest of the country. But due to the climate change phenomenon, warming has been reported in the state. As per the state report on strategy and action plan on climate change drafted in 2012, there has been a rise in temperature in the northwest Himalayan region by about 1.6°C in the last century[2]. This warming of the climate is likely to result in the upsurge or introduction of mosquito borne diseases in Himachal Pradesh. Dengue, an Aedes mosquito-borne diseases, has been reported from Bilaspur, Kangra, and Solan districts of Himachal Pradesh. An effective vector control strategy is required as few foci studies been projected that new transmission windows for malaria may open up in this part of the country by 2030[3],[4]. Therefore, the current study was planned to monitor the insecticide susceptibility status of malaria vectors in six districts of Himachal Pradesh.

Materrial & Methods

Study sites

Himachal Pradesh is divided into 12 districts. Six districts namely Kangra, Una, Mandi, Bilaspur, Solan, and Sirmaur falling under Shivalik and Mid hill zone, and having hilly and forested terrain were selected for the current study. Based on Koppen’s classification, the selected districts fall under Cwa pattern of climate which have subtropical monsoon with mild and dry winter and hot summers. There are four prevalent seasons in Himachal Pradesh, winter (December to February), pre-monsoon (March to May), rainy (June to September) and autumn (October to November). The area is enriched with perennial rivers (Satluj, Yamuna, and Beas), small rivers and a large lake (Gobind Sagar)[5]. Prevalence of malaria is very low (~100 cases annually) in Himachal Pradesh and the state falls under category I as per national strategic plan for malaria elimination. Larval source reduction, focal spray around index cases and IEC activities are the main components of malaria control. Anopheline survey was conducted in two Primary Health Centers (PHCs) of each of the six selected districts [Table 1] and [Figure 1] for evaluation of susceptibility status against three insecticides viz., DDT (4%), malathion (5%) and deltamethrin (0.05%) of public health use. The susceptibility assays were performed using WHO (World Health Organization) insecticide susceptibility kits obtained from Vector Control unit, University of Sain, Malaysia.{Table 1}{Figure 1}

Field survey

Field visits were conducted in August–September, 2019 in selected districts. Female anopheline mosquitoes were collected from cattle sheds and human dwellings using mouth aspirators and torch from 7 am to 10 am. The collected female mosquitoes were provided 10% sugar solution and brought in cloth cages to field laboratory established at district headquarters. Collected mosquitoes were identified up to species level using the standard identification key of Nagpal and Sharma (1995) and separated according to their abdominal conditions[6].

Susceptibility test

Anopheles culicifacies and An. fluviatilis mosquitoes were exposed to insecticide impregnated papers of three insecticides, viz., DDT (4%), malathion (5%) and deltamethrin (0.05%) as per the standard procedure of WHO[7]. Only full fed or semi gravid mosquitoes were used for susceptibility tests after keeping them in holding tubes for one hour. For each of the insecticide bioassay, we exposed three to six replicates of 15–25 mosquitoes per collection from each district. Species wise controls were also used to observe mortality in unexposed mosquitoes. The field laboratory was conditioned for optimum temperature and Relative Humidity during the test i.e., temperature at 27±2 °C and 70±5 % relative humidity. One-hour exposure was given to mosquitoes using exposure tubes and thereafter they were transferred to holding tubes provided with 10% glucose pad. Insecticide exposed mosquitoes were held for 24 h for recording of mortality. After 24 h, mortality of mosquitoes was determined by counting dead mosquitoes. Abbott’s correction formula was applied if mortality in control was found between 5–20%[8]. Based on the mortality of mosquitoes, insecticide susceptibility status of vector mosquitoes was determined as per WHO criteria i.e., a corrected mortality of >98 per cent is susceptible(S), mortality of 90–97% is possible resistance (VR) and mortality <90% indicates resistance (R)[7].

Data analysis

The data of mortality has been expressed in percent mortality which was enumerated using percent formula using Microsoft Excel.

Ethical statement: Not applicable

RESULTS

An. culicifacies was found highly resistant to DDT with (mortality range 8.2–38.7%), whereas against malathion it was, possible resistance to susceptible (mortality range 93.7–98.8%) in four districts viz., Kangra, Una, Mandi and Sirmaur districts. In remaining two districts Bilaspur and Solan, An. culicifacies showed possible resistance against malathion [Table 2], [Figure 2]. In all the districts, An. culicifacies was found susceptible to deltamethrin (mortality range 98.6–100%).{Table 2}{Figure 2}

An. fluviatilis was collected only from two districts, Kangra and Mandi. An. fluviatilis was found resistant to DDT (mortality range 24.6–38.3%) but susceptible to malathion (mortality range 98.5–100%) and deltamethrin (mortality range 98.8–100%) [Table 3], [Figure 2].{Table 3}

DISCUSSION

An. fluviatilis is responsible for malaria primarily in hills and foothills and contributes to about 15% of malaria cases in India[9]. In the current study, An. fluviatilis was found resistant to DDT and susceptible to malathion and deltamethrin in the study sites. In Himachal Pradesh, the first report of resistance in An. fluviatilis against DDT was reported from Shimla in 1979 and thereafter, from Kangra in 1982 whereas Una district was the first district found double resistant i.e., resistant to both DDT and dieldrin[10]. The past data and the present study suggest that resistance against DDT in An. fluviatilis is spreading in the state. Kumari et al., (1998) reported resistance in An. fluviatilis against DDT in 11 districts from eight states of India[10]. Reports of resistance in An. fluviatilis against DDT are also available from Koderma and Gumla district of Jharkhand[11],[12]. But in Odisha, An. fluviatilis was reported susceptible to DDT [13],[14]. In most of the studies undertaken in different parts of the country, An. fluviatilis has been found susceptible to malathion and deltamethrin[11],[12],[13],[15]. But it showed possible resistance against deltamethrin and malathion in a recent study from Gadchiroli district of Maharashtra[16].

An. culicifacies showed resistance against DDT and was susceptible to deltamethrin in all the six districts. An. culicifacies was susceptible to malathion from Kangra, Una, Mandi and Sirmaur district but possible resistance reported from Bilaspur and Solan districts. An. culieifacies has been reported double resistant to DDT and dieldrin in six districts of Himachal Pradesh[10]. The present study confirms these findings; however, it has shown possible resistant status against malathion for the first time in the state. The possible reason of development of resistance towards malathion may be the use of fogging for control of Aedes in the study districts as well as use of malathion in agriculture. In India, An. culicifacies is resistant to DDT in almost entire country[17]. Resistance of An. culicifacies against malathion in the country was reported first time from Gujarat in 1977 and thereafter, it has spread in varying degree[17]. An. culicifacies is susceptible to deltamethrin in most parts of the country but it has been reported resistant to deltamethrin from some states of India such as Assam, Chhattisgarh, Madhya Pradesh and Odisha[18]. An. culicifacies was found susceptible to deltamethrin in one of the foothill regions of northern Himalayan state Uttarakhand[15]. In view of the above facts, further studies on insecticide susceptibility of An. culicifacies against malathion are required to confirm its insecticide resistance status in different parts of Himachal Pradesh.

The present study indicates that availability of vectors of malaria in Himachal Pradesh is quite prevalent. In view of low endemicity of malaria and suspected migratory cases, the evidence of presence of indigenous cases should be generated through vector incrimination studies in different parts of Himachal Pradesh. At present IRS is rarely used as focal spray in Himachal Pradesh. With the advent of climate change, Himachal Pradesh is prone to increase in malaria, therefore the information on susceptibility status of primary malaria vectors will be handy for planning evidence-based IRS at least for focal spray in limited foci reporting malaria incidence.

Conflict of interest: None

Acknowledgements

The laboratory and field assistance provided by the staff of ICMR-National Institute of Malaria Research, Delhi is gratefully acknowledged. Authors are thankful to State Programme Officer (Vector Borne Diseases), Himachal Pradesh for providing logistic support in carrying out the study.

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