Distribution and Breeding Sites of Potential Dengue Vectors in Kandy and Nuwara Eliya Districts of Sri Lanka
Total Page:16
File Type:pdf, Size:1020Kb
Distribution and breeding sites of potential dengue vectors in Kandy and Nuwara Eliya districts of Sri Lanka P. H. D. Kusumawathie1, R. R. M. L. R. Siyambalagoda2 The Ceyion journal of Medical Science 2005; 48: 43-52 Abstract DHF surveillance and control measures in these areas is an urgent need to reduce Entomological investigations were con morbidity and mortality, and the spatial ducted in 26 urban and semi urban areas in distribution of DF/DHF in the two districts. Kandy and Nuwara Eliya districts to Since, the breeding sites differed from one determine the distribution and breeding sites period of time to another and from one of potential vectors of dengue, viz., Aedes locality to another, dengue control measures aegypti Linnaeus and Aedes albopictus should be planned based on local and Skuse in these areas. Aedes larval surveys current entomological information. were carried out around suspected/ serologically positive dengue fever (DF)/ Key words: Ae. aegypti, Ae. albopictus, Kandy, dengue haemorrhagic fever (DHF) cases in Nuwara Eliya. dengue transmission areas, and, in bus depots, government institutions and tyre shops (high risk places for Aedes breeding) Introduction in DF/ DHF non transmission areas. Aedes aegypti Linnaeus is important as the primary vector of dengue fever (DF) and Aedes aegypti and Ae. albopictus were not dengue haemorrhagic fever (DHF) in tropical encountered in the Nuwara Eliya town countries of the world. Aedes albopictus Skuse (altitude 1900 m). But, either Ae. albopictus or is considered as a secondary vector of DF in Ae. aegypti and Ae. albopictus were South East Asia and the Western Pacific (1). encountered in all the other localities (elevation 100 -1300 m). The majority (96%) In Sri Lanka, DF was first reported in early of breeding sites of Ae. aegypti and Ae. 1960s (2). Since then, sporadic, progressively albopictus comprised of water storage large and more frequent DF/DHF outbreaks containers, discarded receptacles and occurred in the country. Over the past 10 tyres. Breeding sites of Ae. aegypti and Ae. years, the morbidity, mortality and the albopictus differed from one locality to spatial distribution of the disease increased another as well as from one time period to considerably with 15,434 suspected and another. serologically positive DF/DHF cases and 88 deaths for the year2004. At present, DF/DHF This study shows that the areas situated is endemic in many urban and semi urban below 1300 m elevation in Kandy and areas, and has invaded new areas, making Nuwara Eliya districts are receptive for the disease an important public health dengue transmission. Strengthening of DF/ problem in the country (3). 1. Regional Office, Anti Malaria Campaign, No. 43/50, Talumtta, Kandy. 2. Director, Anti Malaria Campaign Directorate, Narahenpita, Colombo 5. 44 P. H. D. Kusumawathie, R. R. M. L. R. Siyambalagoda Occurrence of seasonal/periodic peaks of larval surveys. In DF/DHF transmission DF/DHF in dengue endemic areas and areas in the districts, Aedes larval surveys emergence of new foci of transmission in were carried out around the suspected and hitherto DF/DHF transmission free areas are serologically positive DF/DHF cases that important problems faced by the dengue were notified mainly by the government control programme in the country. hospitals. In hitherto DF/DHF non Information on the distribution of Ae. aegypti transmission areas, the surveys were carried and Ae. albopictus and their breeding sites in out in and around bus depots, government a particular area would definitely help to institutions and tyre shops (high risk plaies take timely and appropriate preventive and for Aedes breeding) as these institutions control measures to reduce the morbidity, reported frequent Ae. aegypti and Ae. mortality and the spatial distribution of the albopictus breeding. During each survey, a disease. This study was carried out to minimum of 100 houses within a 200 m determine the distribution and breeding sites radius around the DF/DHF case or the high of Ae. aegypti and Ae. albopictus in Kandy risk institution were visited, all possible and Nuwara Eliya districts of Sri Lanka. Aedes breeding sites were examined and 20 larvae from each positive container were Methods collected randomly by pipetting or dipping, depending on the nature of the breeding Study area habitat. If a particular container had less This study was carried out from January 2003 than 20 larvae, all larvae were collected. The to December 2004 in the Kandy and Nuwara larvae were placed in separate containers Eliya districts of Sri Lanka. The study area (one container per one habitat), staged and comprises of plain and hilly areas with a identified as 3rd and 4th stages using land area of 3,681 km2 and an estimated mid standard keys (4, 5). The lsl and 2nd stage year population of 2.04 million, for the larvae were allowed to develop to 3rd and year 2004 (Chief Secretariat, Planning and 4th stages, and the pupae to become adults Monitoring Division, Kandy). According to prior to identification. If, Ae. aegypti and/or the Regional Epidemiologists in the Ae. albopictus were not encountered in a Kandy and Nuwara Eliya districts, the particular area at the first survey, two more Kandy Municipality and the adjoining surveys at more than 3 month intervals were urbanized areas in the Divisional carried out in the same area. Aedes mosquito Director of Health Services (DDHS) areas, density was determined by the Container namely, Gangawatakorale, Harispattuwa, Index (CI = percentage of containers positive Kundasale, Pathadumbara, Udunuwara for Ae. aegypti and Ae. albopictus) for Ae. and Yatinuwara are endemic for DF/DHF. aegypti and/or Ae, albopictus. The Nuwara Eliya district has reported a few mini outbreaks during the past few years. Breeding sites of Ae. aegypti and Ae. albopictus were categorized into 5 groups, viz., Entomological investigations carried out in (1) water storage containers (water storage the area cemented tanks and iron and plastic barrels), Twenty six urban and semi urban areas (2) discarded receptacles in the domestic and located at different altitudes in 24 DDHS peridomestic environment (discarded plastic areas in the Kandy and Nuwara Eliya containers, pots, bottles, coconut shells, districts were randomly selected for Aedes polythene, metal ware and tins), (3) tyres, Potential dengue vectors in Kandy and Nuwara Eliya 45 (4) domestic appliances (refrigerator trays, high CI values for Hasalaka (38%), Hatton flower vases and ant traps) and (5) others (11%), Madawala (11%), Pundaluoya (18%) (eg., bamboo stump, leaf axils, concrete slabs and Walapane (75%). High CI for Ae. and roof gutters). The relative importance of albopictus, were observed in Hasalaka (25%), each category of containers for Ae. aegypti Madugoda (15%), Rikillagaskada (12%) and and Ae. albopictus breeding was determined Walapane (100%) (Table 4). based on the percentage positivity of each type of container for Ae. aegypti and Ae. albopictus breeding. Discussion Dengue and DHF is a disease complex caused by four serotypes of the dengue virus, Results namely, Dengue 1,2,3 and 4. The disease is Of the 26 study sites, neither Ae. aegypti nor transmitted by Ae. aegypti and Ae.albopictus Ae. albopictus was encountered in the (1, 6, 7). Thus, natural transmission of Nuwara Eliya town. Ae. albopictus was DF/DHF depends on the presence of the encountered in Kalapitiya, Kurunduwatta, dengue virus, Aedes vector mosquitoes Hataraliyadda, Madugoda and Panwila. and a susceptible population. Both Ae. aegypti and Ae. albopictus were reported from the rest of the localities According to serological studies carried out (Figl). in Sri Lanka, the World Health Organisation (1985) reported DF in towns that are situated Ae. aegypti and Ae. albopictus were below an altitude of 1200 m (2). Vitarana encountered primarily in water storage (1986) too, reported that dengue was containers in Ambagamuwa, Bulugoho- prevalent in areas below the altitude of 1000 tenna, Galagedera, Galaha, Gampola, m (8). However, these studies have not Hijjapura, Kandy, Madawala, Poojapitiya, sufficiently dealt with the entomological Rikillagaskada and Talaruoya; in discarded aspects of DF/DHF in these areas. In the receptacles in Daulagala, Hataraliyadda present study, Ae. aegypti and Ae. albopictus and Kalapitiya; and in tyres in Hangu- were encountered even at elevations of 1300 ranketha, Hasalaka, Hatton, Madugoda, m, making the areas that are situated below Pundaluoya and Walapane (Table 1). 1300 m receptive for DF/DHF transmission. Also, the density of Ae. aegypti and Ae. In a particular area, the types of breeding albopictus remains high in some areas, sites of Ae. aegypti and Ae. albopictus differ especially, Hasalaka, Hatton, Madugoda, from one period of time to another (Table 2). Pundaluoya, Rikillagaskada and Walapane, making these areas highly receptive for Water storage tanks are the most preferred DF/DHF transmission. Thus, strengthening breeding site of Ae. aegypti and Ae. albopictus of DF/DHF surveillance and control while discarded receptacles and tyres serve measures, specially in urbanized areas as important breeding sites of the two vector situated below 1300 m elevation is of mosquito species (Table 3). importance in reducing morbidity, mortality and the spatial distribution of DF/DHF. In the study sites that were positive for Ae. aegypti and Ae. albopictus breeding, the In the absence of a specific treatment or a CI for Ae. aegypti varied from 1 to 75%, with vaccine for DF/DHF, vector control is of 46 P. H. D. Kusumaivathie, R. R. M. L. R. Siyambalagoda Map showing the study sites & occurrance or Ae. aegypti & Ae. albopictus in Kandy & Nuwara Eliya Districts N A • Study Sites p Ae. albopictus •k Ae. aegypti Figure 1 Table 1. Number and % (given in parentheses) of different types of containers positive for Ae. aegypti and Ae. albopicus in the study sites in Kandy and Nuwara Eliya districts: January 2003 - December 2004. DDHS area Locality Number (%) of containers positive for Ae.