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Home , Aedes aegypti, Aedes albopictus, Aravalli Range, Garhjat Hills, Utkal Plains, Vindhya Range

Prevalence of aegypti and – Vectors of Dengue and Dengue haemorrhagic fever in North, North-East and Central *

By N.L. Kalra Consultant ( Research Centre), 20 Madhuban, Vikas Marg, – 110092 S.M. Kaul Joint Director, National Malaria Eradication Programme, 22 Sham Nath Marg, Delhi – 110054 and R.M. Rastogi Malaria Unit, WHO/SEARO, – 110002

Abstract The was found to be prevalent in the western, northern, Indo- Gangetic and eastern , Assam valley and the coastal areas of Orissa state in India. The species was non-existent in the Himalayan region. In north-central highlands, the species showed low-to-moderate prevalence, while in south-central highlands, the mountainous areas were largely free but high populations of the vector were encountered in the valleys. Similarly, the eastern plateau, including the were comparatively free of the vector except large towns in the basin. The Satpura ranges of north Deccan were also found to be free of Ae. aegypti. The elevation, type of relief, terrain, density of population, water storage practices in drought- prone regions and high rainfall leading to formation of secondary foci had direct relationship with the prevalence of the species. Altitudes above 1000 metres were found to be unfavourable for the species. Being hygroscopic, the species depicted a phenomenon of ‘annual pulsation’. It tends to move to ‘mother foci’ in the central parts of cities which are humid during the dry season and spreads out during the wet season. Aedes albopictus was encountered in the peripheral areas of towns where it replaced the Ae. aegypti populations. However, in the eastern plateau, the species penetrated upto the central parts, probably due to lack of intra-species competition from aegypti which is very scanty in the region. The information proved to be of immense value in delimiting areas which were prone to DF/DHF epidemics. The internal dynamics provided useful information for developing control strategies.

* This study was funded by the Indian Council of Medical Research, New Delhi

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suspected vector in the country. This Introduction paper high-lights the results of five years Dengue epidemics have been known to of inquiry. occur over the last two centuries in tropical and subtropical areas of the world. However, the role of the mosquito Aedes Study areas aegypti as the vector of this arbivirus has been known only during the past 70 The study covered ten physiographical years(1). In 1953-54 a new disease regions of India, viz. (i) Himalayan region; syndrome associated with dengue (ii) Western plains; (iii) Northern plains; appeared in the , which later (iv) Indo-Gangetic plains; (v) Eastern spread throughout south-east Asia and the plains; (vi) Central highlands; (vii) North Western and South Pacific. Unlike classical Deccan; (viii) Eastern plateau; (ix) Coastal dengue which causes only morbidity, this plains of Orissa, and (x) Assam valley and disease entity affected young children and the states of Jammu & Kashmir, Himachal caused severe illness with haemorrhage Pradesh, Punjab, , Chandigarh, and shock, resulting in high mortality, and , , Madhya earning a name for itself as dengue Pradesh, , Orissa, and haemorrhagic fever/ dengue shock (Fig.1). syndrome or DHF/DSS.

In India, the association of Material and methods haemorrhagic manifestations were noticed for the first time in an outbreak in Calcutta In the present study the conventional in 1963. In this outbreak both the viruses, methods of Aedes survey as adopted by i.e. dengue and , were found the National Institute of Communicable (2) Diseases (NICD) for outbreak studies were to be circulating together . Since then the (4) country has reported several dengue followed . As the scope of the study was outbreaks in different parts of the country limited to determining the distribution of the with manifestations of haemorrhagic species, the information was collected on symptoms in varying degrees. To assess the following aspects: the receptivity of different geographical areas of the country to this infection, an (i) Occurrence (as evinced by attempt was made to determine the indigenous breeding), and distribution of Aedes aegypti in 1968, (ii) Intensity of infestation (No. of based upon the museum collection of the houses found positive per ward) National Institute of Communicable Diseases(3). Since this collection was not House (premises) Index : represen-tative of the whole country, a No. of houses positive for compre-hensive study was launched in Aedes larvae 1969 to assess the extent and intensity of ______X 100 the prevalence of Aedes aegypti, the No. of houses examined known vector of DF/DHF, and its associated species Aedes albopictus, the

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Figure 1. Pysiographical Regions of India Surveyed for Aedes aegypti and Aedes albopictus

For information collection, 10 to 40 Observations towns, depending on size and population, were selected in each region. Towns/cities During the period 1969-1973, a total of were divided into wards/ localities and 50 203 towns/cities covering ten physiogra- houses selected at random were phical regions corresponding to dry and wet seasons were surveyed, except examined in each ward. Wherever the Assam, Kashmir valley and towns in West aegypti population reached the peripheral Bengal which were surveyed during the limit, the searches were extended to the dry season only. The houses in towns/ adjoining rural areas as well. Each region cities investigated during dry and wet was surveyed twice corresponding to dry seasons for Aedes aegypti and Aedes season (March to June) and wet season albopictus are included in Inserts B and C. (July to October). An analysis of the data indicated the following patterns of distribution. Searches were carried out in domestic, peridomestic and extra-domestic habitats. 1. Himalayan region Tree holes were the principal habitats A total of 20 towns spread over south examined under extra-domestic situations. Kashmir , Punjab Himalayas, Kumaon hills and eastern Himalayas were

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Prevalence of Aedes aegypti and Aedes albopictus–Vectors of Dengue and DHF in India investigated. The majority of the areas The Aedes aegypti population depicted investigated had an elevation above 500 low-to-moderate rates of positivity, except metres. The region was found to be in water-scarce areas of Haryana completely free of Aedes aegypti. Aedes (Ambala, Panipat, Rewari and Rohtak), albopictus was found to be the where a large population builds up predominant species in Punjab Himalayas, particularly during the wet season. while in south Kashmir Himalayas and Kumaon hills, its prevalence was scanty. 4. Indo-Gangetic plains 2. Western plains The Indo-Gangetic plains comprise The area includes the arid zone of moving Ganga-Jamuna (which literally sand dunes commonly known as “Thar means area lying between two rivers), desert” situated between the Indus Rohilkhand plains and Avadh plains. Of dunes on the west and Rajasthan upland the of India, the Ganga-Jamuna in the south-east. The area is very thinly doab is by far the largest and most fertile populated due to extreme scarcity of water. and densely populated area. The elevation and character of the flood plains The Aedes aegypti population seems change within the doabs. On the east are to be fully entrenched in the area and the low-lying Rohilkhand and Avadh shows perennial prevalence. In Sikar, it plains. These plains are seamed with was found to infiltrate into rural areas deserted rivers. The Ramganga and during the wet season. Water scarcity and Sarda rivers meander through the the resulting water storage practices were Rohilkhand plains and lower reaches of determined as the main factor for the high Gomti and Ghaghra flow through the build-up of Aedes population. Avadh plains. On the north, these plains are bordered by the narrow waterless Aedes albopictus was encountered sandy belts of Bhabar and the swampy both during dry and wet seasons in the belt of alluvial soil (), supporting vast peripheral areas of towns/cities. expanses of marshy land with luxuriant growth of vegetation.

3. Northern plains The Aedes aegypti population seems The region includes the plains of Punjab to have achieved ecological stability in the and Haryana. Major rivers in the Punjab Ganga-Jamuna doab areas. Most of the region are Sutlej and Beas, which have towns were found to be positive both long mountainous courses and provide a during dry and wet seasons, indicating a large network of canals for irrigation perennial prevalence of the species. purposes. The south-western parts of Proximity of the towns near the two great Haryana face an acute shortage of water. rivers, which provide riverine routes for the The whole area is densely populated and dispersal of the species and high density is one of the richest wheat-growing areas of human population, seems to have of the country.

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Prevalence of Aedes aegypti and Aedes albopictus–Vectors of Dengue and DHF in India provided a foothold to the species in this The Aedes aegypti populations region. showed a definite relationship with the terrain. These were found to be quite Both in Rohilkhand and Avadh plains, stable both in the south Bihar plains and the aegypti population were detected in the Bengal basin. Both the regions are wet season only, except in some large vulnerable to repeated introduction of the towns (e.g. Lucknow and Jaunpur) or species through the Ganga, which has a towns which are situated on the bank of lot of riverine traffic. Both in north Bihar the river Ganga (e.g. aranasi). A gradual and north Bengal plains the species was decline in the incidence of the species either absent or had a scanty prevalence. could be observed as one proceeded This may be due to the terrain features towards the swampy and marshy Terai which support exten-sive vegetation and and Bhabar regions in the north. lack navigational facilities in its river system. The Aedes albopictus populations were more pronounced in the Rohilkhand and Aedes albopictus was found in Avadh plains than in Ganga-Jamuna doab. negligible numbers in peripheral areas of This may be due to the abundance of large towns. natural vegetation cover provided by the forested areas in the region. 6. Central highlands 5. Eastern plains The Central highlands is a wide belt of hilly country bordered on the west by the The eastern plains are further divided into and on the south by the north Bihar plains, south Bihar Plains, . This physiographical north Bengal plains and Bengal basin. The region separates the Great Plains from Ganga flows along the southern border of peninsular plateaus. It is further divided the north Bihar plains, receiving on its left into two divisions, namely, north-central bank three of the major Himalayan rivers - highland, which includes the Aravalli Ghaghra, Gandak and Kosi. A long line of range, east Rajasthan uplands, Madhya marshy stretch extends from east of Bharat pathar and uplands. Chhapra to Khagaria. North Bengal plains The Aravalli range extends south-west for extend from the foot of the eastern a distance of 800 km, in which Abu Hills Himalayas to the northern limits of the (1722 m) is the highest peak. East Bengal basin. The region is drained by Rajasthan uplands lie on the east of tributaries of the Ganga and the Aravalli, ranging in height from 250 to 500 Brahmaputra. South of Duars, the plains metres. Madhya Bharat pathar are more flattish and get waterlogged. The is ð @ÂèÒÜÎ èÌÈê ط à Bengal basin embraces most of the alluvial plains of West Bengal and æêäÌÂÆÊ\@¨ÐÊ@ ÐÂÚÄÂØ@ÐÂæ@ includes the great Ganga delta. Æêè@Â@ÈÊÊà@ÂÜÈ@îÒÈÊ@ìÂØØÊò @ÒÜ@èÐÒæ@ÂäÊÂ\@ êäèÐÊä@Ê æè@lie the Bundelkhand uplands.

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The south-central highlands include 7. North Deccan the plateau, which is built of lava with rolling surface and flat-topped North Deccan is part of the peninsular forested hills with a number of flowing plateau which is one of the largest rivers. East of the Malwa plateau is a physiographical divisions of India. North series of plateaus at different levels Deccan comprises the Satpura range and collectively known as Vindhyan scarp- the Maharashtra plateau. The Satpura lands. On the south it is bordered by the broadens out considerably in the central . Skirting the roots of the part bordered on the north by the Vindhya range and sandwiched between Mahadeo hills and on the south by the Vindhya and Satpura extends the Gwalgarh hills. Narmada valley from east to west. Ae. aegypti was found to be com- Aedes aegypti depicts differential pletely absent in this region. This may be patterns of prevalence in the north-central due to the hilly of the terrain, which and south-central highlands. In north- has been observed to be inhospi-table for central highlands the species is fairly the species in India. However, Ae. widespread particularly in the east albopictus was the common species Rajasthan uplands and Malwa plateau. encountered in the region during the wet Water scarcity and the resultant water season. storage practices seem to be the single most important factor promoting the stability of the species. It is less common in 8. Eastern plateau Madhya Bharat pathar because of the hilly and forested nature of the region. The Eastern plateau has a much more diversified topography than the Deccan South-central highlands are compara- plateau. It comprises the Chhota Nagpur tively free of A. aegypti except in large plateau, , the Mahanadi basin towns situated in the Narmada valley and the Dandakarnya area. The Chhota (Jabalpur and Sagar), which showed year- Nagpur plateau consists of perfect basin round prevalence of the species. In other surrounded by hills rising from 600 to large towns of the region, the species was 1000 m. Dandakarnya is also a forested detected during the wet season only. and hilly area.

Aedes albopictus also depicted a The Eastern ghats are essentially a similar pattern of distribution. It was much coastal range. This range exhibits its true more pronounced in north-central mountain character between the Godavari highlands and was scanty in south-central and the Mahanadi. highlands. The species was always encountered in peripheral areas. Aedes aegypti are commonly unstable in this area. Low densities of the species were encountered in the industrial towns of Dhanbad and Jamshedpur in the Chhota Nagpur plateau. In other towns the species

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Prevalence of Aedes aegypti and Aedes albopictus–Vectors of Dengue and DHF in India seemed to infiltrate during the wet season The upper Assam valley, because of its from the adjoining south Bihar plains. marshy nature, is sparsely populated, while the lower Assam valley is densely In the eastern plateau, the species was populated. The areas receive heavy found restricted to towns situated in the rainfall from south-western monsoons. Mahanadi basin only where it perhaps got introduced from the coastal plains. The The survey was carried out only during eastern ghats were found to be free of the dry season and it was observed that aegypti population. Aedes aegypti was endemic in the entire valley. House indices were observed to be Aedes albopictus was the dominant quite high. species in the region, particularly in the eastern plateau. The species was found to Aedes albopictus was the dominant invade practically entire towns during the species in the peripheral areas of towns wet season. and was detected in high densities.

9. Coastal plains of Orissa Conclusions The of Orissa are The studies carried out in north and north- much drier and wider than their indicated that Aedes aegypti counterpart in the west. These are also was endemic in the western plains (Thar known as and include the desert), northern plains (Punjab and Mahanadi delta. Haryana), Indo-Gangetic plains, eastern plains (Bihar and Bengal basin), Assam Out of the ten towns surveyed in the valley and the coastal areas of Orissa. region, five towns situated on the coast The species was found to be completely were found positive for Aedes aegypti non-existent in the Himalayan region. In both during dry and wet seasons. In the north-central high-lands, the species other five towns which had proximity to the showed a low-to-moderate prevalence, but hilly terrain of the eastern ghat and in south-central highlands, the Gharjat hills were found negative for the mountainous areas were largely free but species. Aedes albopictus continued to be high populations were recorded in the the dominant species in this region and Narmada valley. The eastern plateau, was encountered in both dry and wet including the eastern ghats, were seasons. comparatively free except some prevalence in the towns situated in the Mahanadi basin. The Satpura ranges of 10. Assam valley north Deccan were also found to be free of Ae. Aegypti. The valley, occupied by the middle course of the Brahmaputra, stretches for nearly The Aedes aegypti population in this 600 kms. The valley is linked with the region depicted a terrain-bound pheno- Ganga plains by the plains of north Bihar. menon as determined by Kalra et al (3).

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The elevation, type of relief, terrain, including tree holes, in this region. This population density and water storage showed continued dependence of the practices were found to have a direct species on man for food and shelter and relationship with the prevalence of the complete absence of any sign of species. The species depicted a high ecological adaptation towards feral situa- prevalence in areas up to an elevation of tion which increases its epidemiological 500 metres. These included plains, potential. coastal areas and river valleys. Aedes albopictus was encountered in In areas with the elevation ranging the peripheral areas of towns where it from 500 to 1000 metres, which included replaced the aegypti population. However, mountainous areas and plateaus, the in the eastern plateaus, the species was species was found to be scanty. Elevation found to be endemic which had pene- higher than 1000 metres seems to be the trated into the central parts of towns/ least attractive to it. cities. This may be partly due to the In the plains, the species was found to absence of intra-species competition from be widespread in densely populated towns Ae. Aegypti, which is very scanty in this while the rural areas were found to be region. completely free. Introduction of the species into rural areas is a recent phenomenon associated with rural water supply schemes. Utility of the information collected The Aedes aegypti population depicted a phenomenon of ‘annual pulsation’. The The data collected under the inquiry population showed a definite reduction helped in delimiting the areas prone to during the dry season and expansion Aedes-borne epidemics. The information during the wet season due, respectively, was also supplied to concerned state to the drying up and availability of governments to enable them to take breeding sites. preventive measures against dengue outbreaks. The dengue outbreaks in Both drought conditions and high (5) (6) rainfall were found to encourage a high (1969) , and Gwalior (1970) are build-up of Ae. aegypti population. In the classical examples. The information former case, water storage practices due broadly holds good even today. to water scarcity, and in the latter case, abundant availability of secondary foci in Besides, the data provided useful domestic and peridomestic areas promoted information on the bio-ecology of the growth of high vector populations. species for planning future studies.

A complete absence of breeding was observed in extra-domestic habitats,

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2. Sarkar JK. Calcutta experience and findings in Acknowledgement haemorrhagic fever and Chikungunia fever epidemics. Jap. J. Med. Sci. Biol. 1967, 20 The authors gratefully thank the Director, (suppl):88-90. National Institute of Communicable Diseases, Delhi, and Dr B.L. Wattal, former 3. Kalra NL, Wattal BL and Raghvan NGS. chief of the Division of Medical Distribution patterns of Aedes (Stegomyia) Entomology and Vector Control, for their aegypti in India. Some ecological considerations. Bull. Ind. Soc. Mal. Com. Dis. 1968, 5:307-34. guidance and support in the conduct of these studies. Thanks are also due to 4. Kalra NL. Aedes survey of Vishakhapatnam Messrs H.V. Aggarwal, John Koshy and following an epidemic of febrile illness in 1964. M.K.Dutta, Research Assistants, and to Bull. Ind. Soc. Mal. Com. Dis. 1965, 2:33. other staff for their valuable contributions in 5. Kalra NL et al. Epidemiological and entomological the field. study of an outbreak of in Ajmer, Rajasthan, in 1969. J. Com. Dis. 1976, 8:261-279. Reference 6. Arora DD et al. Epidemic of Dengue fever (DEN-3) 1. Gratz NG and Knudsen AB. The rise and spread at Gwalior. J.Com. Dis. 1973, 5:11. of dengue, dengue haemorrhagic fever and its vectors. WHO, Geneva, 1996, CTD/FIL (DEN) 96-7:1-197.

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Insert B during Aedes aegypti dry and wet seasons Districtwise House Indices for Indices House Districtwise

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Insert C during Aedes albopictus dry and wet seasonsdry House Indices for

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