INT J CURR SCI 2016, 19(1): E 183-189 RESEARCH ARTICLE ISSN 2250-1770 Prevalence of Dengue vectors during outbreaks of Dengue viral infections in certain Panchayat unions of Tirunelveli District, Tamil Nadu, India Malarvizhi Mariappan and Sakkanan Ilango* Department of Zoology, Ayya Nadar Janaki Ammal College (Autonomous), Sivakasi-626 123, Tamil Nadu, India *Corresponding author: silangovan@yahoo.com Abstract Dengue virus is mainly transmitted by the Aedes aegypti and Aedes albopictus and causes dengue fever that are widely distributed throughout the tropical and subtropical countries. Dengue fever (DF) and its more serious forms, dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), are becoming important public health problems in India, especially throughout Tamil Nadu. Therefore, there is an urgent need for the rapid detection of dengue virus infections in the acute phase of illness in order to provide timely clinical treatment and monitoring of vectors prevalence to reduce the transmission of dengue virus. The present results revealed the serological and entomological survey which was carried out from April 2014 to March 2015 in certain panchayat union of Tirunelveli district. Totally 139 breeding places with water were observed for the presence of Aedes larva, among them 53 Cement Cisterns were recorded as positive, with a breeding preference ratio (BPR) of 1.13. The total number of suspected blood samples screened during study period was 148, out of which 40 (27.02%) samples were positive for IgM antibody. The most affected age group was 6-12 yrs followed by 13-18 yrs. Both Container index as well as Primary infection of dengue was highest during December 2014 and May 2015. The data obtained from this study revealed that the population of Aedes larvae is directly proportional to the IgM positive cases and mostly Cement cisterns and plastic container were the preferable breeding places for mosquito larvae. Keywords: Aedes larvae; Container Index; Dengue Fever; MAC-ELISA Received: 05 th December 2015; Revised: 20 th December; Accepted: 04 th January 2016; IJCS New Liberty Group 2016 Introduction Dengue is an endemic mosquito transmitted arboviral disease with an estimated 3.97 billion people at risk in developing countries (Brady et al., 2012). In southern India, among 30 districts of Tamil Nadu, 29 districts were found infected with dengue infections which include DHF outbreaks in Chennai, Dharmapuri, Tiruchirappalli and Virudhunagar districts etc. (Kabilan et al., 2003; Simmons et al., 2012; Rajesh et al., 2013; Wilson et al., 2014). Dengue virus (DENV) belongs to the family Flaviviridae, There are four known distinct serotypes (DENV I-IV) which causes a spectrum of illness ranging from in apparent infection to moderate febrile illness and severe and fatal hemorrhagic disease. In recent years, dengue hemorrhagic fever (DHF) by hemorrhagic signs in infected cells and is also caused dengue shock syndrome (DSS) and is characterized by features of DHF plus evidence of circulatory failure manifested by hypotension or hypertension, cold clammy skin and restlessness, which emerged as a major public
health problems, with expanded geographic distributions and increased epidemic activities (Butt et al., 2008). DENV is mainly transmitted to human by the day time biting female Aedes mosquitoes (Aedes aegypti and Materials and Methods Study area Nanguneri, Valliyur, Kalakadu and Radhapuram panchayat union are located in southern part of Ae albopictus) (Sharma et al., 2000). However, the Tirunelveli district. Their geographical coordinates are 8 principal vector, Ae.aegypti is extensively distributed in many towns and cities of India. Ae.albopictus is considered as a secondary vector and known to be present in the district of Tirunelveli (Tandon et al., 2000; Perich et al., 2000). They rest indoors mainly in living rooms and bed rooms and are active during dawn and dusk. The increases man-vector contact and contributes difficult by in controlling disease transmission (Johannon et al., 2009). Their altitudinal ranges, density and distribution could be linked to global and local changes resulting from temperature, rainfall, humidity and seasons, varying latitude and altitude along with vehicular movements, growth in human populations, and their activities attributable to outbreaks of dengue vectors (WHO, 1997; Gautam et al., 2009; Dhimal et al., 2014). Early laboratory diagnosis of dengue virus infection is important and is routinely done by serological test. Antidengue IgM antibodies appear as early as 3 days after infection and remain in circulation for 1 to 2 month. Anti dengue IgG antibodies appears after 1 week, peaks after 2 to 3 weeks and remain lifelong in circulation. Many laboratories are performing for early diagnosis of dengue infections that is possible by detecting IgM- ELISA technique (Gupta et al., 2005). Therefore, present study was undertaken to find out the outbreaks of dengue infections in certain panchayat unions of Tirunelveli District using MAC-ELISA technique and correlated with Aedes breeding preference ratio. 29' 0" North, 77 40' 0" East and 8 16' 0" North, 77 42' 0" East. It has an average elevation of 141 metres. Mostly these areas receive rainfall in North East, South West Monsoon. The study areas were selected based on prevalence of mosquito density and dengue outbreaks. Sample collection The blood samples were collected from only suspected patients, who had two or more of the signs and symptoms relating to dengue such as head ache, high fever, rashes, myalgia, arthralgia and also blood obtained from Private, public hospital laboratories, primary health centre and where ever possible by practiced staff nurse. The samples were collected within 3-7 days following the onset of illness. Approximately, 1 ml of blood was collected and brought back to laboratory; serum was separated and stored at -20 o C. Then the serums were directly screened for detection of IgM by MAC-ELISA technique. Samples screening Suspected sera were directly screened against dengue virus using Dengue IgM capture enzyme linked immune sorbent assay (MAC-ELISA). Briefly, 125 μl of peroxidase-labelled anti dengue monoclonal antibody conjugate was added in the microwell containing dengue antigen (antigen plate), resulting in the formation of antigen antibody complex. Within 10 mins of addition of conjugate to the antigen plate, 100 μl of 1:100 diluted serum and control were added to another plate (assay
plate) containing anti-human IgM antibodies attached to microwell test strips. The assay plate was incubated at 37 C for one hour and then washed. After 100 μl of complex antigen conjugate solution was transferred from the antigen plate to assay plate which was further incubated for one hour. After incubation, the microwells were washed and 100 μl of tetramethyl benzidine/ hydrogen peroxide (TMB/H 2 0 2 ) substrate solution was added to each well. After 10 mins of incubation at room temperature, stop solution was added to each well and the color density of the residue (optical density) was read within 30 mins at the wavelength of 450 nm. Patients with positive anti dengue IgM were considered positive cases for dengue viral infection. A primary infection was indicated if IgM/IgG index ratio was more than 1.2 and as secondary case if this ratio is less than above value (Shu et al., 2003). All collected data were later on statistically analyzed. Prevalence of dengue vectors The dwellings for Aedes larvae were identified and collected from the selected places which had experienced recent dengue cases during monsoon and post monsoon seasons. Most potential breeding places for Aedes larvae such as cement cisterns, potted plants, grinding stones, plastic ware, Earthen ware etc. were examined and collected using pipette, dropper, spoon, beaker based on the nature of breeding habitats. The collected immature larvae were transfer to plastic container and brought back to the laboratory for further identification. The suspected larval species were reared under laboratory condition and the emerged to adult mosquitoes were further identified on the basis of different morphological characters by using taxonomic keys. A total of 139 wet containers were examined and they were categorized into seven container types; coconut shell, Plastic container, Earthen wares, unused tyres, cement cisterns, Grinding stones and potted plants. Based on data obtained, container index (CI) and breeding preference ratio (BPR) of dengue vectors for different container were calculated using statistical tools. Results and Discussion During the study period, a total of 148 suspected blood samples were analyzed. Out of these, 40 (27.02%) samples were positive for dengue viral specific IgM antibodies (Table 1). Age and sex wise distribution of dengue cases were recorded in table 2. Totally, 23 males and 17 females were detected among the 40 samples. The higher positive cases of dengue infection were noted among males than females. The male-to-female ratio was 2:1 which is similar with other studies (Gupta et al., 2005; Ukey et al., 2010; Kumar et al., 2010). Few researcher reported (Neeraja et al., 2006) that there is higher seropositive in male than female. This might be due to male exposed outer more than the females and females stay at home more than males. So, it showed male predominance. The most affected age group was 6-12 yrs children followed by 13-18 yrs group people that were noticed in this study. The IgM-positive cases were higher among children followed by younger adults. The vector is active at day time, particularly at shade of tree or nearby buildings. The children used to play near school and because of urban area, they prone to roam near vegetative area where the sun is not so bright and they can be easily exposed to get mosquito biting. Moreover, all the people were prepared to take rest at shade of tree and outside places. Therefore, there is more chance to affect by the dengue disease. However, several studies revealed that, dengue has been reported to mainly a pediatric public health problem
Table 1. Detection of dengue virus from suspected blood samples in selected blocks by MAC-ELISA technique Name of the Panchayat Nanguneri Kallakadu Radhapuram Valliyur No. people contacted 128 85 135 93 No. blood samples collected 52 23 46 27 Dengue Positive Dengue Negative n % N % 19 5 9 7 36.53 21.73 19.56 25.92 33 18 37 20 63.46 78.26 80.43 74.07 Total 441 148 40 27.02 108 72.97 Table 2. Age and sex wise distribution of IgM cases among dengue positive samples Age in years 1-5 6-12 13-18 19-36 >36 Distribution of dengue IgM positive cases Male % Female % 3 13.04 2 11.76 11 47.83 6 35.29 5 21.73 6 35.29 3 13.04 2 11.76 1 4.34 1 5.88 Total 23 57.50 17 42.50 Table 3. Comparison of area wise container index with Dengue virus positive cases Panchayat Nanguneri Kallakadu Radhapuram Valliyur Total container observed 106 89 148 98 No. (+) container 43 24 42 30 Container Index (%) 40.56 26.94 28.37 30.61 Dengue positive (%) 36.53 21.73 19.56 25.92 Table 4. Breeding preference ratio with different breeding habitats in selected panchayat union of Tirunelveli District Type of container Container X Container Y BPR (Y/X) observed with water (%) with larvae (%) Coconut shells 11 7.91 3 5.66 0.71 Plastic containers 24 17.26 10 16.98 1.09 Earthen ware 18 12.94 7 13.20 1.02 Potted plant 16 11.51 4 7.54 0.65 Waste tyres 9 6.47 2 3.77 0.58 Cement Cistern 53 38.12 23 43.39 1.13 Grinding stone 8 5.75 3 5.66 0.98 Total 139 100 53 100 - (Shah et al., 2006; Anderson et al., 2007). The maximum number of positive cases was reported in month of December 2014 (initial stage of North east Monsoon) with second peak in month of May 2015 (Pre monsoon). Mostly, Nanguneri and Radhapuram blocks get rainfall during November- January (initial stage of North east Monsoon and Post North east monsoon). Maximum number of dengue cases observed during December 2015. The reason behind this is, on the month of December which is known to be post rainy season due to rain water gets stagnant and they become the source for the mosquitoes to breed. The present findings were supported by (Dar et al., 2003; Chandralekha et al., 2008; Bharaj et al., 2008), the presence of stagnant water after rain fall favors the mosquito breeding which leads in an increased occurrence of dengue. During Pre monsoon season, high levels of dengue positive cases were present because of
water scarcity. Due to over exploitation, there was water scarcity in the area of Radhapuram and Valliyur. Breeding preference ratio estimates the degree of breeding affinity of dengue vectors towards a particular container type. A total of 441 containers were examined and 139 containers were found to be positive for Aedes breeding sites (Table 3 and 4). Major types of breeding places found in this area included coconut shells, potted plant,grinding stones cement cisterns, Earthen wares, plastic wares and unusable tyres. The positivity percentage by type of container amounted to: cement cisterns (1.13), plastic wares (1.09) and earthen wares (1.02). Other and a coordinated community effort to increase awareness about how to control the dengue vectors and environmental education strategies are also important for reducing the dengue vectors. Acknowledgement We profoundly thank the UGC, New Delhi for providing financial support to carry out this project under Major Research Project Scheme. We are also thankful to the Management and Principal, Ayya Nadar Janaki Ammal College, Sivakasi for provided great support by making the availability of various institutional facilities. References Anderson KB, Chunsutiwwat S, Nisalak A, Mameen P, studies conducted in Philippines (Mahilum et al., 2005) Libarty D, Rothman AL (2007). Burden of and in India (Singh et al., 2008) also recorded the highest positivity of immature dengue vectors in discarded tyres. However, people get used to store water on cans, tins and other vessels which are not closed which favours mosquito for breeding and laying eggs. The water storage containers remained filled with water and undisturbed for long durations to meet the daily water requirements for diverse purposes of humans and other domestic animals. All these water storage practices are favorable to give rise to breeding of Aedes mosquitoes (Swaddiwudhipong et al., 1992). The present findings showed a higher number of Aedes larvae in the selected places which is associated with the higher number of dengue cases and breeding preference ratio also indicated the degree of larval breeding affinities toward particular container type and the results indicate discarded containers were the preferable breeding habitat for the dengue vector. Therefore, prevention and control of dengue virus is beset with many challenges and requires high political commitment, multi-sectoral collaboration symptomatic dengue infection in children at primary school in Thailand: a prospective study. Lancet 369: 1452-1459. Bharaj P, Chanar HS, Pandey A, Diddi K, Dar L, Guleria R (2008). Infections by all four dengue virus serotypes during an outbreak of dengue in 2008 in Delhi, India. J Virol 5: 1. Brady OJ, Gething PW, Bhatt S, Messina JP, Brownstein JS (2012). Refining the Global Spatial Limits of Dengue Virus Transmission by Evidence-Based Consensus. PLoS Negl Trop Dis 6: 1760. Butt N, Abbassi A, Munir SM, Ahmad SM, Sheikh QH (2008). Haematological and biochemical indicators for the early diagnosis of dengue viral infection. J Coll Physicians Surg Pak 18: 282. Chandralekha Gupta P, Trikha A (2008). The north Indian dengue outbreak 2006: A retrospective analysis of intensive care units admissions in a tertiary care hospital. Trans R Soc Trop Med Hyg 102: 43-147.
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