Research Article Introduction Prevalence of Aedes aegypti - The vector of Dengue/ Chikun fevers in Bangalore City, Urban and Kolar districts of Karnataka state N Balakrishnan *, Rakesh Katyal **, Veena Mittal **, LS Chauhan ** Abstract Karnataka state in general, particularly Bangalore city and surrounding districts, have been reporting the incidence of Dengue and Chikun cases in recent years. Entomological surveillance on the prevalence of dengue vector mosquito Aedes aegypti has been carried out by the NCDC team during 2012 in some of selected localities of Bangalore City, Bangalore urban and Kolar districts of Karnataka state. The results of the study revealed that widespread vector mosquito breeding and the Aedes larval breeding indices viz., House, Container and Breteau for total study area were 23.9, 11.6 and 43.0 respectively. Of the 10 localities surveyed, 9 showed House and Breteau indices above the critical levels. The breeding of Ae. aegypti was mainly found in cement tanks (19.3%), metal containers (11.9%), plastic containers (10.1%) and other containers (6.3%), and their Breeding Preference Ratio (BPR) has also been computed for the various habitats surveyed. In order to effectively control Dengue and Chikun incidence in the study area, initiation of routine vector surveillance and control activities added with Information Education and Communication (IEC) measures and community intervention are necessitated. Keywords: Dengue, Chikun, Vector surveillance, larval breeding indices, Vector breeding preference, Bangalore city, Bangalore urban and Kolar districts, Karnataka. Dengue and Chikun are the vector borne viral diseases, that are widely distributed in many tropical and subtropical countries of the world. An estimated 50 million dengue infections occur every year while Chikun comes as periodic epidemics and both are transmitted by the Aedes vector mosquitoes. These diseases are closely associated with poor environmental sanitation, inferior housing and inadequate water supplies. In India, Dengue and Dengue Hemorrhagic Fever (DHF) have been restricted to urban and peri urban areas of the country. However, in studies carried out in Karnataka as well as from neighboring Tamil Nadu state, it has also been reported from rural areas. This was mainly attributed to large scale developmental activities, rapid growth of transport system, industrial and construction activities and provision of safe piped drinking water have resulted in the establishment and proliferation of Aedes mosquitoes in many areas. In Karnataka state, higher incidence of Dengue has been reported in recent years and Chikun has also been reported in large numbers in the recent past. Since Bangalore city and the surrounding districts are contributing the majority of the cases reported in the state, an entomological surveillance on the breeding of the dengue vector has been carried out during June, 2012 in selected localities of Bangalore City, Bangalore urban and Kolar districts of Karnataka state and the results are furnished in this article. Materials & Methods The study area comprised of Bangalore city (Latitude: 12º, 18 N and Longitude 77º, 37 E with an altitude of 929 meters above MSL) and the adjoining Bangalore Urban and Kolar districts of Karnataka state. The Bangalore city has a population of 9. 59 million (2011 census) living in an area of 2190 square kilometers * NCDC, Bangalore Branch, 8, NTI Campus, Bellary Road, Bangalore-560 003, Karnataka. ** National Centre for Disease Control (NCDC), 22, Sham Nath Marg, Delhi 110 054. Correspondence to: Dr N Balakrishnan, Incharge, NCDC Bangalore branch, NTI Campus, 8 Bellary road, Bangaluru-560 003. E-mail Id: drbalanicd@gmail.com ADR Journals 2015. All Rights Reserved.
Balakrishnan N et al. J. Commun. Dis. 2015; 47(4) and is divided into 198 wards. The maximum and minimum temperature of the study area is 33 and 14 degree Celsius respectively with an average rainfall of 859 mm. A total of 10 randomly selected localities/ villages of the study area, comprising 4 areas from two wards (Eijipura and Palace Guttalli) of Bangalore city, two villages namely Attibele and Mayasandra situated in adjoining Bangalore urban district and 2 localities each from Kolar and Bangarpet towns of Kolar district were selected for this study. The entire study area is facing a shortage of water supply since it is provided at irregular intervals and the people are forced to store it in their houses in all available storage containers for a long period which ultimately facilitate the Aedes mosquito larval breeding. Results The data on the incidence of Dengue and Chikun fever cases for the period of 2008-2012 showed that in Karnataka state, many of the total 30 districts are reporting the incidence of Dengue cases and also deaths in a few districts. However the Chikun cases were reported only from some of the districts during the above period (Table 1). In Karnataka state among all the districts, Bangalore city is contributing a large number of cases (28.8% of dengue and 21.6% of Chikun cases reported in the state during the reporting period) whereas the same phenomenon has also been observed in some of the adjoining districts of the city. Since Aedes aegypti, the vector of Dengue and Chikun is found to breed in domestic and peri domestic water storage containers, in order to assess its endemicity levels, an entomological survey on Aedes vector larval breeding has been carried out by using single larval technique. 1 In the randomly selected study localities, the NCDC team has carried out door to door survey to find the Aedes larval breeding in the available wet containers present in the houses and surroundings. The larvae collected from the breeding habitats were transported to laboratory and the adults emerged were identified using standard identification keys. The particulars of houses, containers surveyed and number positive for Aedes larval breeding were recorded area wise and the standard larval indices viz., House, Container and Breteau indices were computed. The particulars of various larval breeding habitats contributing larval breeding have been collected from the survey and the breeding preference ratio (BPR) has also been computed. The data on the incidence of dengue and Chikun for the Karnataka state and the study localities during the period of 2008 to 2012 have been obtained from the state health authorities. The particulars of surveyed localities, houses and containers surveyed and the indices computed for Bangalore City, Bangalore urban and Kolar districts of Karnataka state are given in Table 2. The number of houses searched in different study localities varied from 10 to 50 which was mainly attributed to the factors such as cluster of houses, availability of houses for survey and the distance between the houses in a survey period of 3 hours. A total of 251 houses were searched for the prevalence of Aedes larval breeding and 60 were found positive for it. During the survey, a total of 1010 containers were searched and 104 were found positive for Aedes larval breeding with the container index of 10.2 and the Breteau index computed for the study area was 43.0. While comparing larval breeding indices of the various study districts, the Kolar district was found to have the house, Container and Breteau indices 28.9, 13.8 and 71.6 respectively showing higher values than Bangalore City, whereas the above indices were 23.9, 11.6 and 37.3 respectively in Bangalore city. In the adjoining villages of Bangalore urban district, they were 9.5, 4.2 and 9.5 indicating that in villages also the vector is getting established and in future it may result in the outbreaks of the diseases. Place 2008 2009 2010 2011 2012 Cases Cases Cases Cases Cases Cases Cases Cases Cases Cases (Death) Karnataka 339 (3) 1008 1764 (8) 3239 2285 (7) 1430 405(5) 255 3924(21) 205 State Bangalore 67(0) 74 505(1) 1001 801(0) 225 77(0) 20 1059(4) 4 City Bangalore 13(0) 23 104(1) 106 126(2) 34 11(0) 5 210 (4) 3 Urban Kolar 49(2) 6 68(0) 264 144(0) 86 15(0) 25 237(2) 7 Table 1.Incidence of Dengue and Chikun fever cases in Karnataka and study area during 2008-2012 ISSN: 0019-5138 20
J. Commun. Dis. 2015; 47(4) Balakrishnan N et al. S. No. Locality House index Container index Breteau index Hs +ve Hi (%) Cs +ve Ci (%) Bangalore urban district 1 Mayasandra village 10 2 20 21 2 5.5 20 2 Attibelle 32 2 6.25 74 2 2.7 6 Total 42 4 9.5 95 4 4.2 9.5 Kolar district 1 Marikuppam- bangarpet 16 4 25 47 9 19.1 56 2 Bangarpet railway colony 15 3 20 51 4 7.8 26.6 3 Sydan b. Darga street, kolar 23 6 26 202 14 6.9 60 4 Clock tower street, kolar 20 8 40 82 26 31.7 130 Total 74 21 28.3 382 53 13.8 71.6 Bangalore city 1 21 cross street, eijipura 20 10 50 63 17 26.9 85 2 Eijipura 50 12 24 141 19 13.4 38 3 Vayali kaval area 35 7 20 136 7 5.1 20 4 Guttahalli area 30 6 20 111 8 7.2 26.6 Total 135 35 25.9 451 51 11.3 37.7 Grand total 251 60 23.9 928 108 11.6 43 Table 2.Locality wise House, Container and Breteau indices of Aedes aegypti recorded in Bangalore city and surrounding Bangalore urban and Kolar districts In Kolar district and in Bangalore City, the house and Breteau indices were more than critical levels and in Bangalore urban district also, one out of two villages surveyed recorded above critical levels. The particulars of various containers surveyed and the containers found breeding for Ae aegypti larvae and the Breeding Preference Ratio (BPR) computed for the study are given in Table 3. In all the study localities, Ae. albopictus was found absent during the survey. A total of 1010 wet containers were recorded from all localities of the survey of which 104were found to support Aedes larval breeding. The water holding containers available in the study area in the order of abundance were plastic containers-602 (59. 6%), Miscellaneous containers (plastic bottles, tea cups, coconut shells etc.)-142 (14.1%), Cement tanks-124 (12.3%), Metal containers-84 (8.3%), Earthen pots-33 (3.3%) and Discarded tyres-25 (2.5%). The Aedes larval breeding has been recorded to be found mainly in cement tanks-24 (19.3%), metal containers-10 (11.9%), plastic containers-61 (10.1%) and other containers-9 (6.3%). Among the different types of containers surveyed, the plastic containers due to easy availability and affordability, were the major water holding structures in all study localities. The Breeding Preference Ratio (BPR) has also been computed from the Aedes mosquito breeding survey data recorded in the study. Cement tanks (1.88) were found to be the most preferred breeding habitats followed by metal containers (1.15), plastic containers (0.98) and other miscellaneous containers (0.61). Water in these containers is stored for longer durations and these containers are never emptied, cleaned and replenished periodically, making them as the prolific breeding sites. Type of containers Number of containers with water Percentage Breeding Preference Examined (x%) With Aedes larvae (y%) Positive Ratio (BPR) (Y/X) Cement tank 124 (12.27) 24 (23.07) 19.35 1.88 Metal containers 84 (8.32) 10 (9.61) 11.90 1.15 Plastic container 602 (59.60) 61 (58.65) 10.13 0.98 Other miscellaneous 142 (14.05) 9 (8.65) 6.33 0.61 Tyres 25 (2.47) 0 - - Earthen Pot 33 (3.27) 0 - - Total 1010 104 Table 3.Infestation of Aedes aegypti by containers and Breeding Preference Ratio in the study area 21 ISSN: 0019-5138
Balakrishnan N et al. J. Commun. Dis. 2015; 47(4) Discussion Many workers have studied the distribution, seasonal prevalence and the breeding pattern of Ae. aegypti from various Indian cities. Reuben (1970) has reported from a study on the seasonal prevalence of adults of Ae. aegypti in Vellore (Tamil Nadu). 2 The population density was low from February to June and rose to a peak during wet seasons between September to December. The reestablishment of Ae. aegypti population from Pune city and its surroundings (Maharashtra) was not reported earlier where as Geevarghese et al. had reported from a reconnaissance survey and they also studied seasonality of the distribution and abundance of Ae. aegypti and factors governing the same. 3 Two strains of dengue virus from infected patients as well as Ae. aegypti mosquitoes were collected from Bangalore city. 4 The prevalence of Ae. aegypti in Bangalore city was elucidated by Soman (1977) and it was found to breed in used tyres, drums, other containers and also in tree holes, and its density was directly correlated with rainfall. 5 In Delhi aftermath of the dengue outbreaks, the impact of intervention measures against information, education and communication (IEC) in houses and offices and supplemented by legislative measures by the Municipal Health Authorities has resulted in a remarkable decline in the incidence of Dengue Fever/ DHF during the period of 1996 to 2000. An entomological investigation has been carried out during the outbreak of dengue in Tiruppur town and neighboring rural areas (Tamil Nadu) and the Aedes larval indices were above the critical levels in both urban as well as in rural areas. Effective control of dengue from this area necessitated undertaking of routine monitoring and undertaking of necessary control measures. 6 Katyal et al. have carried out entomological investigations in Dengue/ DHF affected Bangalore city during 2002. 7 The larval breeding indices of Ae. aegypti was above the critical levels among 19 out of 22 localities surveyed. The larval breeding was mainly found in cement tanks and flower pots and other containers. In another study, Katyal et al. have reported the risk factors involved in the transmission of Dengue Fever/ DHF in some selected localities of Jaipur (Rajasthan). 8 The results showed that Aedes larval breeding in houses were above the critical levels of 10% and 20% respectively. The acute scarcity of water led to the storage practices which facilitated the prolific breeding of Ae. aegypti resulting in repeated outbreaks and the hence the need for IEC activities have been emphasized. Dengue is primarily an urban disease however, in recent studies carried out in the state it is evident that rural areas also have all the potential features for breeding of vector and results in dengue outbreaks. In Karnataka state, it is evident that dengue and Chikun are prevalent in many of the districts, however the Bangalore City and neighboring districts contributed for a large number of cases. Since Chikun cases are also found to have been recorded from many districts, in future it may result in probable outbreaks of the disease. The results of the entomological surveillance have shown that the house index and Breteau index were above critical levels in all the localities surveyed in Bangalore city as well as in Kolar district and also from one village in Bangalore Urban district. Even though the localities surveyed have piped water facilities, supply of water is not regular and intermittent and the people are forced to store water in available containers. The larval breeding was mainly found in cement tanks, metal and plastic containers. In the study area, there are no routine surveillance and Aedes larval control operations being carried out by the state health authorities except in some towns and Bangalore city. Since the higher incidence of Dengue and Chikun have been reported in recent years particularly from Bangalore city and neighboring districts, the above study has been carried out to assess the endemicity. The study results showed that the vector mosquito breeding indices were above the critical levels in many of the localities surveyed which necessitates undertaking of routine surveillance particularly during monsoon and post monsoon periods and application of appropriate control measures to contain the possible outbreaks of these diseases. A regular entomological survey for monitoring Aedes aegypti breeding should be strengthened wherever it is under operation and it needs to be expanded to newer areas of adjoining districts, especially to rural areas. The breeding habitats detected should be subjected to appropriate control measures such as source reduction and timely intervention measures. Intensification of public health education and community intervention for prevention of vector breeding and messages through mass media are necessitated to create public awareness and control of these diseases. References 1. Katyal R, Gill KS, Kaushal K. Seasonal variations in Aedes aegypti population in Delhi, India. WHO/ SEARO Dengue Bulletin 1996; 20: 78-81. ISSN: 0019-5138 22
J. Commun. Dis. 2015; 47(4) Balakrishnan N et al. 2. Reuben R. A note on the seasonal prevalence of Adults of Aedes aegypti in Vellore. Indian J Med Res 1970; 58: 854-55. 3. Varghese G, Kaul HN, Dhanda V. Observation on the Re-establishment of Aedes aegypti population in Poona city and suburbs, Maharashtra state, India. Indian J Med Res 1975; 63: 1155-63. 4. Samuel G, Soman RS. Studies on dengue in Bangalore City: Isolation of virus from man and mosquitoes. Indian J Med Res 1975; 63(3): 396-401. 5. Soman RS. Studies on Aedes aegypti in Bangalore city. Indian J Med Res 1977; 65: 8-16. 6. Balakrishnan N, Venkatesh S, Lal S. An Entomological study on the dengue vectors during outbreak of Dengue in Tiruppur town and its surroundings, Tamil Nadu, India. J Commun Dis 2006; 36(2): 164-68. 7. Katyal R, Saxena VK, Kaushal K, Lal S. Prevalence of Aedes aegypti in dengue/ mdhf affected areas in Bangalore City, Karnataka state, India. Vector borne Diseases: Epidemiology and Control. Tyagi BK (Ed.). Scientific Publishers, Jodhpur on behalf of CRME (ICMR), Madurai 2008: 136-39. 8. Katyal R. Risk Factors involved in the transmission of Dengue/ DHF in some selected localities of Jaipur (RJ), India. J Commun Dis 2011; 43(1): 81-83. 23 ISSN: 0019-5138