Seasonal Prevalence of Aedes aegypti in Five Localities of Delhi, India By
M.A. Ansari and R.K. Razdan (Indian Council of Medical Research) 20, Madhuban, Delhi-110092, India Malaria Research Centre
Abstract Studies were carried out in selected localities of Delhi to detect the presence of Aedes
aegypti, the principal vector of dengue and dengue haemorrhagic fever (DF/DHF) and seasonal fluctuations in immature and adult densities. Results revealed that the breeding index was very high in surveyed localities ranging from 5.3 to 6.9 during the month of September. The highest breeding index (6.9) was recorded in Malaviya Nagar and the lowest in Khelgaon. Similarly, the adult density ranged from 10.7 to 15.2 per man hour during the post-monsoon period and showed positive correlation with immature densities. The occurrence of breeding and adult density throughout the year, particularly in Sadiq Nagar and Malaviya Nagar, revealed that the antilarval measures adapted in the Urban Malaria Scheme were ineffective to check the build-up of the density of Aedes
aegypti. Key words: Aedes aegypti, dengue, dengue haemorrhagic fever (DHF), seasonal prevalence, breeding index.
Introduction
Consequent upon the occurrence of the first DF/DHF outbreak in Calcutta 28
in 1963(1), an Aedes aegypti survey was undertaken in Delhi in 1964 to Dengue Bulletin – Vol 22,1998
Seasonal Prevalence of Aedes aegypti in Five Localities of Delhi
assess the potential threat of DF/DHF. Studies revealed that Aedes aegypti populations were restricted to the walled city (old parts of Delhi) and the peripheral areas recorded only the presence of Aedes albopictus and
Khelgaon, and the survey was carried out from October 1996 to February 1998.
Material and methods The pipette method in tyre dumps and a small stainless steel dipper with iron handle were used for the sampling of
Aedes vittatus(2). Subsequent studies revealed population that in the
Aedes
aegypti a
Delhi
depicted
phenomenon of “annual pulsation”, i.e. the species remained confined to the “mother foci” in humid and cooler parts of the central city and spread to outer areas during the rainy season by establishing a secondary foci(3). a Following the occurrence of the first outbreak of DHF during 1963(1), comprehensive study on the seasonal prevalence and the relative importance of domestic containers in supporting the perennial breeding of
Aedes larvae from evaporation coolers
and large water bodies. Adults were sampled with the help of an aspirator and flash torch. The samples of larvae from different habitats were brought to the laboratory and the larvae were reared in enamel 29±1oC trays at a temperature of and 70-80%
relative humidity for a reconfirmation of species identity. The House index (HI), Container index (CI) and Breteau index (BI) were calculated as per WHO standard procedures. The sampling of larvae and adults was carried out weekly to observe The the seasonal monthly changes in both larval and adult densities. average container indices and adult index were then estimated. Meteorological data was collected from the Safdarjang station located in the south zone of the Municipal Corporation of Delhi. The mean maximum and minimum temperatures and the relative
Aedes
aegypti was undertaken in one of the identified mother foci(2,4). The present study was carried out in newlydeveloped peripheral posh colonies of Delhi which had come into existence after the first survey in 1964 to detect the presence of Aedes aegypti and its seasonal prevalence. The study areas included five localities in New Delhi, i.e. Sadiq Nagar, Malaviya Nagar, Ayurvigyan Nagar, Andrews Ganj, and Dengue Bulletin – Vol 22,1998
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Seasonal Prevalence of Aedes aegypti in Five Localities of Delhi
humidity were correlated with Aedes and adult indices.
breeding index was very low during the extreme cold months (JanuaryFebruary) in all the localities surveyed. The proportion of the domestic and peridomestic breeding of
Results The monthly average of HI, CI, BI and
aegypti is presented in the Fig.I. man-hour Figure density are presented in the 2. Seasonal prevalence of Aedes aegypti in five localities The results revealed that Aedes Table-1. of Delhi (1996-98) aegypti bred in both domestic and The results revealed that the peridomestic sites. However, breeding of Aedes aegypti occurred throughout the year in Sadiq Nagar and Malaviya Nagar. Similarly, adult density was also observed in these localities throughout the year. This is contrary breeding to the reports only that the to was confined peridomestic breeding sites such as discarded containers, flower vessels, tyre dumps and water meter chambers supported the maximum breeding in both dry and wet seasons. The adult density showed a marginal peak in the month of April followed by a sharp decline in the dry month of May and a gradual build-up in successive months. The adult peak was observed between SeptemberNovember (Fig.2).
Aedes
monsoon or post-monsoon seasons. Though the breeding index and manhour density were very low, the immature and adult densities started to build up from June onwards and the peak density was recorded throughout the wet season (August-October). The
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Dengue Bulletin – Vol 22,1998
Seasonal Prevalence of Aedes aegypti in Five Localities of Delhi Table 1. Larval indices and man hour densities of Aedes aegypti in five localities of Delhi during 1996-98 Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec.
SADIQ NAGAR HI CI BI MHD 0.16 0.5 0.1 0.37 0.4 0.02 0.07 0.25 0.8 1.15 0.8 0 1.04 2.5 1.4 6.75 0.61 1.24 1.0 3.25 1.5 3.1 3.3 7.75 1.9 3.2 3.5 7.75 1.7 3.1 3.8 7.0 5.0 6.4 8.2 11.2 3.8 6.8 9.0 10.9 2.5 7.1 5.8 12.5 1.9 2.5 2.0 3.4
MALAVIYA NAGAR HI CI BI MHD 0.09 0.5 0.09 0.25 0.1 0.4 0.05 0.5 0.75 0.9 0.7 2.5 1.79 3.4 2.5 12.0 1.23 2.9 2.4 4.5 2.9 2.1 2.0 8.5 1.9 3.7 4.9 10.7 3.5 3.3 5.0 9.5 5.9 5.7 9.3 15.2 5.6 9.4 8.1 6.6 1.3 1.2 1.6 10.6 2.7 3.5 2.5 9.8
AURVIGYAN NAGAR HI CI BI MHD 0 0 0 0 0 0 0 0 1.0 1.9 1.0 0.5 0.8 2.5 1.2 6.75 0.7 2.0 1.4 3.5 0.3 1.0 1.1 2.5 1.4 3.2 4.0 8.5 1.7 2.7 4.7 13.5 3.0 6.1 7.9 10.7 2.8 7.0 5.0 9.6 1.0 0.5 1.8 10.2 2.0 5.0 1.9 3.5
ANDREWS GANJ HI CI BI MHD 0 0 0 0.1 0 0 0 0 0 0 0 0 1.0 4.1 2.4 9.2 0.32 0.75 0.48 1.5 1.3 3.0 2.0 5.5 KHELGAON HI CI 0 0 0 0 0.17 0.8 1.25 4.4 0.65 3.5 1.09 2.4 1.96 5.2 2.4 3.9 3.6 6.1 1.8 6.3 1.0 2.2 1.5 5.0 0.8 2.9 3.2 8.0 3.2 4.3 6.7 8.2 4.3 7.4 6.2 12.2 5.0 12.4 13.1 7.6 3.8 9.2 6.0 12.1 0.5 0.01 0.6 3.3
Dengue Bulletin – Vol 22,1998
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Seasonal Prevalence of Aedes aegypti in Five Localities of Delhi
BI MHD
0 0
0 0
0.17 1.5
1.96 7.2
1.14 2.2
1.87 3.7
4.2 5.7
4.3 6.2
6.3 10.7
3.2 7.5
1.6 8.6
1.0 1.1
HI = House Index(%), CI =Container Index(%), BI = Breteau Index (per 100 houses) MHD = Man-Hour density
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Dengue Bulletin – Vol 22,1998
Seasonal Prevalence of Aedes aegypti in Five Localities of Delhi
A
comparison
of
the
(15.2) in Malaviya Nagar and lowest (10.7) in Khelgaon]. The occurrence of breeding and adult density throughout the year, particularly in Sadiq Nagar and Malaviya Nagar, revealed that antilarval measures adapted in the Urban Malaria Scheme were ineffective to check the build-up of the density of
meteorological data revealed that the
Aedes breeding was reduced to a very low level when the average temperature varied between 10° and 50°C and the relative humidity ranged between 30% and 40%. The average minimum temperature of about 28°C and 70-80% relative humidity were quite ideal for the proliferation of the breeding of this species.
Aedes aegypti. Since Aedes aegypti breeds in domestic water containers, emphasis should be placed on species sanitation which can also be supplemented by stringent legislative
Discussion During the present survey
aegypti was the only species which was encountered. This may be due to the fact that the survey was confined to well-developed urban localities. This is in conformity with the earlier observations that Aedes aegypti is considered a domestic species and is common in urban situations, while
Aedes
measures. These measures can also be integrated with synthetic as and al.(5) pyrethroid-treated Ansari et al.(6) curtains
demonstrated by Majori et localities in Delhi.
(1998) in selected
References 1. Ramakrishnan SP, Gelfand HM, Bose PN, Sehgal PN, and Mukherjee RN. The epidemic of acute haemorrhagic fever, Calcutta. Ind J Med Res 1964, 52:633-650. 2. Krishnamurthy BS, Kalra NL, Joshi GC and Singh NN. Reconnaissance survey of Aedes mosquitoes in Delhi. Bull Ind Soc Mal Comm Dis, 1995, 2:56-67. 3. Kalra NL, Wattal BL, Raghvan NGS. Distribution pattern of Aedes aegypti in India. Some ecological considerations. Bull Ind Soc Mal Comm Dis, 1968, 3&4:307-334. 4. Rakesh Katyal, Kuldip Singh and Kausal Kumar. Seasonal variations in Aedes aegypti
Aedes albopictus occurs in either transitional areas or rural situations(2). The breeding index was very high in the surveyed localities ranging from 5.3 to 6.9 during the month of September. Nagar and The the highest lowest container (5.3) in index (6.9) was recorded in Malaviya Khelgaon. Similarly, the adult density ranged from 10.7 to 15.2 [highest
Dengue Bulletin – Vol 22,1998
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Seasonal Prevalence of Aedes aegypti in Five Localities of Delhi population in Delhi, India. WHO/SEARO
6. Ansari MA, Neera Kapoor and Sharma VP. Relative efficacy of synthetic pyrethroidimpregnated fabric against mosquitoes under laboratory conditions. J Am. Mosq. Cont. Asso. 1998, 14(4):406-409.
Dengue Bulletin, 1996, 20:78-81. 5. Majori G, Sabatinelli G and Coluzzi M. Efficacy of permethrin impregnated curtains for malaria vector control. Med Vet Ent, 1987, 1:185-192.
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