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Entomological investigations during an outbreak of dengue fever in Lal Kuan town, Nainital district of Uttarakhand, India.

Dengue is a worldwide public health problem spread through out the tropical and subtropical zones. It is endemic in south-east Asia, the Pacific, east and west Africa, the Caribbean and the Americas. Dengue fever (DF) and dengue haemorrhagic fever (DHF) are emerging major public health problems in India and are reported from more than 19 states (1,2). Aedes aegypti Linn. (Diptera: Culicidae) is the principal vector of dengue fever and is widely prevalent in India (3). Dengue virus has also been recently detected in Ae. albopictus Skuse4, which was confined to urban areas, now has spread to rural areas and also spreading in areas which were so far free from this disease (5).

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.


(1.) Sharma SN, Raina VK, Kumar A. Dengue/DHF an emerging disease in India. J Commun Dis 2000; 52(3): 175-9.

(2.) Kumar S, Singh US, Katyal R. Preliminary observation on Aedes aegypti survey during lean transmission season in sub-Himalayan town of India. J Commun Dis 2008; 40(4): 167-8.

(3.) Kalra NL, Kaul SM, Rastogi RM. Prevalence of Aedes aegypti and Aedes albopictus vectors of DF/DHF in north, north-east and central India. Dengue Bull 1997; 21: 84-92.

(4.) Yadav RL, Narasimham MVVL. Dengue/dengue haemorrhagic fever and its control in India. Dengue Newslett 1992; 17: 3-8.

(5.) Kumar A, Sharma SK, Padbidri VS, Takare JP, Jain DC, Datta KK. An outbreak of dengue fever in rural areas of northern India. J Commun Dis 2001; 55(4): 274-81.

(6.) Guidelines for dengue surveillance and mosquito control, II edn. Manila, Philippines: WHO Regional Office of the Western Pacific 2003; p. 105.

(7.) Manual on practical entomology in malaria. Pt II. Methods and Techniques. Geneva: World Health Organization 1975; p. 1-3.

(8.) Nandi J, Sharma RS, Datta PK, Dhillon GPS. Dengue in the National Capital Territory (NCT) of Delhi (India): epidemiological and entomological profile for the period 2003-2008. Dengue Bull 2008; 52: 156-61.

(9.) Balakrishnan N, Venkatesh S, Lal S. An entomological study on the dengue vectors during outbreak of dengue in Tiruppur town and its surrounding, Tamil Nadu, India. J Commun Dis 2006; 58: 164-8.

(10.) Das BP, Kaul SM. Pictorial key to the common Indian species of Aedes (Stegomyia) mosquitoes. J Commun Dis, 1998; 50: 123-7.

Corresponding author: Dr Raj Kumar Singh, Research Scientist, National Institute of Malaria Research (ICMR), Sector 8, Dwarka, New Delhi-110 077, India. E-mail:

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 (%)

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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Article Details
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Author:Singh, R.K.; Dhiman, R.C.; Dua, V.K.; Joshi, B.C.
Publication:Journal of Vector Borne Diseases
Article Type:Report
Geographic Code:9INDI
Date:Sep 1, 2010
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