Dengue

Dengue Bulletin Volume 28 (2004)

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Short Note 4

Essentiality of Source Reduction in both Key and
Amplification Breeding Containers of Aedes aegypti
for Control of DF/DHF in Delhi, India

B.N. Nagpal, Aruna Srivastava^#, M.A. Ansari and A.P. Dash

Malaria Research Centre, 20 Madhuban, Delhi - 110 092

Delhi, the Capital of India, reported the first-ever outbreak of dengue fever in 1967^[1]. Since then the city has experienced cyclic epidemics every 2-3 years. During 1996, a large epidemic swept the city when 10,252 cases were hospitalized and 423 deaths were recorded^[2]. The disease has now become endemic and the yearly incidence has varied between 160 and 300 cases of DF/DHF, with a couple of deaths^[3]. Aedes aegypti has been invariably found to be associated with these outbreaks in Delhi. Overhead tanks (OHTs) and ground level tanks (GLTs) as key containers, and evaporation coolers have repeatedly been reported as seasonal amplification sites^[4,5]. The key containers maintain mosquito breeding throughout the year, whereas coolers amplify the Aedes population from May to November, and thereafter they go dry^[6].

During 2003, DF/DHF resurged in some localities in Delhi and a total of 2,604 DF/DHF cases and 33 deaths were registered up to 9 November city Municipal Corporation of Delhi (MCD). The MCD organized a campaign aimed at source reduction, which was backed by vehicle-mounted thermal fogging for the control of the outbreak. However, the reduction in the DF incidence was not found to be commensurate with the inputs made into the campaign. At the request of the MCD, a team of experts from the Malaria Research Centre undertook a comprehensive survey in five affected localities, viz. Dayanand Colony (Lajpat Nagar Phase IV), Lajpat Nagar (Phases I and II), Kotla Mubarakpur, Dayalpur Extension and Harsh Vihar – Tulsi Niketan, to identify both the key containers (OHTs and GLTs) and the amplification containers (evaporation coolers, earthen pots, flower vases, household ornamental fountains, etc.) during November 2003 as per WHO techniques. The results of the study are included in this communication.

The results of the larval survey of Aedes aegypti in five dengue-affected localities in Delhi as mentioned above are given in the
Table. The results revealed that among the key containers, out of 243 OHTs and 20 GLTs, 64 OHTs (26.34%) and 8 GLTs (40%) were found positive for breeding of Aedes aegypti. On the other hand, out of the 533 evaporation coolers, which are identified as the major amplification-breeding site, checked, none was found positive for breeding of Aedes aegypti. Ornamental fountains inside the drawing rooms and mud-pots containing water for birds were supporting the heavy breeding (>1,000 larvae in each site) of Aedes aegypti. The maximum positivity of OHTs was found in Kotla Mubarakpur (39.39%), followed by Phases I and II of Lajpat Nagar (30%) and Dayanand Colony (20.69%). Two OHTs located on the roofs of the market area were found supporting the breeding of Aedes albopictus. In a children’s home for boys belonging to the Social Welfare Department of the Delhi Government, five out of 12 OHTs were found positive for Aedes aegypti while two were found dry. It would thus appear that during the MCD campaign, source reduction efforts had concentrated on evaporation coolers, and key containers and other trash materials breeding the species remained intact in domestic habitats.

IEC Activities of MCD

The IEC activities of the MCD generally covered the following aspects:

1.      Creating awareness through media and spreading vocal messages through the use of loudspeakers in DF-affected localities, distribution of pamphlets, etc.;

2.      MCD workers who visit houses for physical verification of breeding sites also interact with householders and impress upon them to remove small water collections indoors/outdoors, specially water evaporation coolers.

3.      During the survey it was found that fogging generally lacked a ‘pre-fogging public information campaign’ requiring the public to keep the house doors/windows open to permit the entry of fog. Health workers, while interacting with householders, invariably talked about the removal of breeding from coolers and tanks but did not point out other sites of breeding. The crosschecking teams of the MCD also laid emphasis on inspection of evaporation coolers as focal points and did not verify OHTs/GLTs and trash materials, as they found it a time-consuming affair. In urban areas, for security reasons or houses being locked, access by health workers into the houses was also a constraint.

4.      In view of the aforesaid, it can be concluded that: (i) source reduction should cover both the key containers as well as the amplification breeding sites, viz. evaporation coolers and other trash articles breeding the vector species; (ii) the fogging operation should be preceded by a pre-fogging information campaign in order to seek full cooperation of communities to derive optimal benefits from fogging; (iii) the IEC campaign based on KAP studies should be prepared with particular emphasis on community participation; (iv) special efforts should be focused on behavioural change in accordance with the guidelines laid down by WHO^[7]; and (v) health staff of the MCD should be trained in entomological surveys/techniques related to Aedes breeding, prevention and its control.

Acknowledgement

The authors are thankful to Dr K.N. Tiwari, Municipal Health Officer-cum-Director, Health Services, Municipal Corporation of Delhi, for providing assistance in the conduct of the study, and to Mr N.L. Kalra, former Deputy Director, National Vector-Borne Diseases Control Programme, for his valuable suggestions and guidance. We acknowledge the efforts of the field staff for assisting in carrying out the survey. Thanks are also due to Mr Sanjeev Gupta for his help in various ways.

References

1.      Balaya S, Paul SD, D'lima LV and Pavri KM. Investigations of an outbreak of dengue in Delhi in 1967. Indian Journal of Medical Research, 1969, 57: 767-774.

2.      Sharma S, Sharma SK, Mohan A, Wadhwa J and Dar L. Clinical profile of dengue haemorrhagic fever in adults during the 1996 outbreak in Delhi, India. Dengue Bulletin, 1998, 22: 20-27.

3.      Katyal R, Kumar K, Gill KS and Sharma RS. Impact of intervention measures on DF/DHF cases and Aedes aegypti indices in Delhi, India: an update 2001. Dengue Bulletin, 2003, 27: 163-167.

4.      Krishnamurthy BS, Kalra NL, Joshi GC and Singh NN. Reconaissance survey of Aedes mosquito in Delhi, Bull Ind Soc Mal Com Dis, 1965, 2: 56-67.

5.      Ansari MA and Razdan RK. Seasonal prevalence of Aedes aegypti in five localities of Delhi, India. Dengue Bulletin, 1998, 22: 28-32.

6.      Katyal R, Gill KS and Kumar K. Seasonal variation in Aedes aegypti population in Delhi, India. Dengue Bulletin, 1996, 20: 78-81.

7.      Parks W and Lloyd L: Planning social mobilization and communication for dengue fever prevention and control. A step-by-step guide. WHO, Geneva, 2004.