Entomological investigations during an outbreak of dengue fever in Lal Kuan town, Nainital district of Uttarakhand, India.
Lal Kuan is a small town with a population of 18,524 (2001 census) and surrounded by many villages situated at the foothills of sub-Himalayan Kumaon region in Nainital district of Uttarakhand state. It has irregular piped water supply resulting in water storage practices for household purposes and has a Century Pulp Paper Mill (CPPM). Migratory labour poses an increased risk of vector-borne diseases, including dengue fever and DHF in this region.
An outbreak of dengue was reported during August to September 2009. As of October 2009, a total of 1285 fever cases and 286 clinical suspected cases of dengue were admitted in different hospitals. Of which, 43 were dengue fever cases confirmed by the National Institute of Communicable Diseases, Delhi (based on serology kits for IgG and IgM antibodies). About 10 deaths were reported during the outbreak in 2009, which could not be attributed to dengue alone. Necessary efforts were taken by the district health authorities (DHA) to contain the epidemic.
At the request of the state health department, detailed entomological investigations were carried out from 27 September to 2 October 2009 in 14 randomly selected localities. A door-to-door survey was carried out in houses and peri-domestic areas to detect Aedes breeding with a view to study the prevalence, distribution, stratification of areas for Aedes mosquitoes and to identify high risk areas in the town prone to dengue/DHF outbreak. The larval collections were made simultaneously in each locality following the single larval technique of WHO (6) to find out the Aedes breeding in all the wet containers present in and around the houses and their premises in the study areas.
All kinds of breeding habitats in the study area like cemented tubs/tanks, overhead tanks, iron/metal drums, junk material, desert coolers, discarded tyres and curing tanks, etc. were screened with the help of flash-light and pipette, while bigger containers were searched with the help of a dipper of 300 ml capacity (having white background for better visibility). The type of breeding habitats and their locations were recorded. The data on larval survey were analyzed and calculated in terms of different indices like container index (CI), house index (HI), breteau index (BI), pupal index (PI) as per the WHO procedure (7).
The container preferences of Aedes breeding were assessed by calculation of breeding preference ratio (BPR).
A total of 418 houses were searched for Aedes breeding in all kinds of temporary and permanent water bodies both indoors and outdoors in all the residential and commercial areas of the town. Breeding was detected in 197 houses. About 3079 water containers were searched for Aedes breeding, of which 1095 were found positive for Aedes breeding. The over all HI, CI, BI and PI were 47.12, 45.98, 261.96 and 25.11%, respectively (Table 1).
Among all the habitats, highest positivity of Aedes larvae was recorded in earthen pots (25.93%) followed by plastic drums/tanks/tubs (19.36%), discarded tyres (18.81%), plastic containers (10.31%) and desert coolers (9.95%) (Table 1). In addition, breeding was also observed in daubers, overhead tanks, old discarded plastic shoes, junk materials, flower vases, cemented tanks/tubs and metal containers and curing tanks during the survey. BPR was observed to be highest in flower vases (1.62) followed by daubers (1.54), discarded tyres (1.39), plastic OHTs (1.34) and cemented tanks/tubs (1.25).
In Lal Kuan town, during the survey, different larval and adult stages of Aedes were recorded in all the dengue-affected localities and, breeding and average MHD of vectors were found to vary from locality-to-locality. In Delhi also, the distribution pattern of Ae. aegypti and disposition varied from ward-toward (8). The present study results also confirm to those observed in Haldwani by Kumar et al (2). The authors also reported that water containers lying indoors were the preferred breeding habitats of Ae. aegypti and Ae. albopictus (2). Another study conducted on Aedes mosquitoes in Tirupur town also support the results of the present study (9). Balakrishnan et al (9) observed that water containers which were kept indoors were rarely cleaned and remain undisturbed most of the time, thus, resulting in high breeding of Aedes mosquitoes and water storage habits were found as one of the factors responsible for high Aedes breeding (9).
The adult Aedes mosquito collections were also carried out to determine the biting activity of mosquitoes with the help of aspirators and flash-lights in the morning hours (0700-0900 hrs) (7) in 14 dengue affected localities, and identified up to species level with the help of standard identification keys (10). Areawise man hour density (MHD) of Ae. aegypti and Ae. albopictus mosquitoes for each locality ranged between 0-27 and 0-32, respectively (Table 2). The average MHD of Ae. aegypti and Ae. albopictus was 8 and 10.07, respectively. Since the MHD above one is the critical level, it necessitated the appropriate control measures to control the outbreak of dengue in these localities.
Though an outbreak of dengue was reported for the first time in August 2009, it was confirmed by the Department of Health Services, Govt. of Uttarakhand, in the first week of September 2009 while fever cases increased sharply from second week of September and declined rapidly by the end of September 2009. All entomological indices were above the critical level and potential cause of this seems to be the compulsion of storing water in different containers without cover, to meet the acute shortage of water in the area. Since most people work as labourers in the CPPM, they might not be aware of the conditions or factors that can exacerbate mosquito breeding.
Aedes breeding indices and adult densities have been recorded above the critical levels imply their potential for future outbreaks. This is mainly attributed to change in ecology, cultural and social behaviour of population, life style changes, non-availability of tap water supply enforcing water storage in containers etc. The reporting of dengue and high density of dengue vectors might be due to rise in temperature making it favourable for transmission of dengue. Therefore, in order to contain the occurrence of DHF/DF, entomological surveillance should be undertaken effectively in the known endemic localities and the information should be utilized to forecast the possibility of future outbreaks of DHF/DF, so that necessary control measures could be undertaken to avoid any dengue outbreak in future. Introduction of dengue virus in the Lal Kuan community might be due to influence of internal migratory labour working in the CPPM industry from the adjoining city of Haldwani. In the recent past, Haldwani has experienced/recorded an outbreak of dengue in 2007.
From the present investigations, it can be concluded that Aedes larval and adult stages were detected in the transmission season in Lal Kuan town, Nainital district with most of the areas showing high adult and larval indices, which are probabaly the reasons for sudden spurt of dengue fever cases. The preventive strategy needs to be directed towards minimizing the breeding potential of Aedes by adopting one/ two days bottom up programme every week, and water management practices by individuals along with implementation of urban bye-laws as well as special IEC activities. Further study is warranted to elucidate the reason for development of foci of dengue in Lal Kuan town which was hitherto free from dengue and for further prevention of occurrence of epidemics.
Key words Aedes aegypti; Ae. albopictus; breeding index; dengue; dengue haemorrhagic fever; larval index
The authors are thankful to the technical staff of NIMR, Shri Harikesh Gupta and Shri N. Keshav Rao, for their active involvement and assistance during the field survey.
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Corresponding author: Dr Raj Kumar Singh, Research Scientist, National Institute of Malaria Research (ICMR), Sector 8, Dwarka, New Delhi-110 077, India. E-mail: email@example.com
Received: 12 April 2010
Accepted in revised form: 8 July 2010
R.K. Singh [a], R.C. Dhiman [a], V.K. Dua [a] & B.C. Joshi [b]
[a] National Institute of Malaria Research (ICMR), New Delhi; ^District Malaria Office, Nainital & Udham Singh Nagar, India
Table 1. Prevalence indices of Aedes species in different localities of Lal Kuan town, Nainital district of Uttarakhand Localities Houses Houses Containers searched visited positive searched Motahaldu 39 20 457 Nagina Colony 45 21 332 Bangali Colony 38 17 192 Nai Basti 8 3 38 CPPM Colony 61 36 249 25 Acres Colony 21 9 68 Rajeev Nagar 16 6 63 Bindukhatta 18 3 111 Railway Colony 21 13 69 Sanjay Colony 18 11 84 Shramik Colony 73 33 327 Main Road 9 6 56 Hathikhana 29 11 128 Ghoranala 22 7 207 Total/Average 418 197 2381 Localities Containers Pupae HI (%) searched positive collected Motahaldu 192 16 51.28 Nagina Colony 147 12 46.66 Bangali Colony 74 8 44.73 Nai Basti 13 -- 37.50 CPPM Colony 197 24 59.01 25 Acres Colony 33 5 42.85 Rajeev Nagar 27 3 37.50 Bindukhatta 33 -- 16.66 Railway Colony 26 2 61.90 Sanjay Colony 37 3 61.11 Shramik Colony 182 21 45.20 Main Road 32 6 66.66 Hathikhana 35 4 37.93 Ghoranala 67 1 31.81 Total/Average 1095 105 47.12 Localities CI (%) BI (%) PI (%) searched Motahaldu 42.01 492.30 41.02 Nagina Colony 44.27 326.66 26.66 Bangali Colony 38.54 194.73 21.05 Nai Basti 34.21 162.50 0 CPPM Colony 0.79 322.95 39.34 25 Acres Colony 48.52 157.14 23.80 Rajeev Nagar 42.85 168.75 18.75 Bindukhatta 29.72 183.33 0 Railway Colony 37.68 123.80 9.52 Sanjay Colony 44.04 205.55 16.66 Shramik Colony 55.65 249.31 28.76 Main Road 57.14 355.55 66.66 Hathikhana 27.34 120.68 13.79 Ghoranala 32.36 304.54 4.54 Total/Average 45.98 261.96 25.11 Table 2. Man hour density of Ae. aegypti and Ae. albopictus in Lal Kuan town, Nainital district of Uttarakhand Localities Ae. Ae. Ratio of Ae. searched aegypti albopictus aegypti & Ae. albopictus Motahaldu 9 17 1:2 Sanjay Colony 3 5 1:1.6 Bangali Colony 8 16 1:2 Nai Basti 3 8 1:2.6 CPPM Colony 17 12 1.4:1 25 Acre Colony 21 6 1:3 Rajeev Nagar 3 3 1:3 Bindukhatta 5 7 1:2.3 Railway Colony 9 4 1.1:1 Nagina Colony 27 22 1:2.4 Shramik Colony 2 32 1:1.2 Main Road 2 0 -- Hathikhana 3 4 1:1.3 Ghoranala 0 5 -- Average MHD 8 10
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|Author:||Singh, R.K.; Dhiman, R.C.; Dua, V.K.; Joshi, B.C.|
|Publication:||Journal of Vector Borne Diseases|
|Date:||Sep 1, 2010|
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