In this study we examined the costs and effectiveness of using larvivorous fish, Poecilia reticulata, and a chemical larvicide, temephos, in anopheline mosquito control in the riverbeds below the major dams in Sri Lanka. Five riverbeds below the dams, namely Laxapana, Kotmale 1, Kotmale 2, Nilambe, Rantembe and Victoria, were selected. Riverbed pools in Laxapana and Kotmale 1 were treated with P. reticulata; Rantembe and Victoria were treated with temephos; and Kotmale 2 and Nilambe were kept as controls. In each area, the anopheline larval density, before and after application of fish/temephos, was estimated. The cost of application of fish/temephos was estimated by activities involved for each treatment. After intervention, there was a significant reduction in anopheline larval density in the fish-treated areas compared with the temephos-treated and control areas. Application of P. reticulata was 2.67 times less costly than that of temephos. The cost of fish application can be further reduced if the community is involved in the application.
The larvivorous potential of Poecilia reticulata was studied in the laboratory and in the field. In the laboratory, the number of anopheline larvae consumed per fish per day and the number of larvae in fecal matter per fish were determined. In the field study, 29 of 60 selected riverbed pools in Kotmale oya, below the Kotmale dam, were stocked with P reticulata, whereas the rest served as controls. Anopheline larval surveys were carried out starting from 1 day prior to stocking of fish and on selected days subsequently. P. reticulata consumed an average of 117 +/- 32.33 larvae per fish per day. Fecal matter of P. reticulata contained an average of 2.7 +/- 2.68 larvae per fish . There was a significant reduction in the number of pools positive for anopheline larvae (P < .001) after stocking fish and the number of larvae per pool (P < .001) and per 100 dips (P < .001) as compared with controls.
IntroductionDengue has emerged as a major public health problem in Sri Lanka. Vector control at community level is a frequent and widespread strategy for dengue control. The aim of the study was to assess Aedes mosquito breeding sites and the prevention practices of community members in a heavily urbanized part of Colombo.MethodsA cross-sectional entomological survey was conducted from April to June 2013 in 1469 premises located in a subdistrict of the City of Colombo. Types of breeding sites and, where found, their infestation with larvae or pupae were recorded. Furthermore, a questionnaire was administered to the occupants of these premises to record current practices of dengue vector control.ResultsThe surveyed premises consisted of 1341 residential premises and 110 non-residential premises (11 schools, 99 work or public sites), 5 open lands, and 13 non-specified. In these 1469 premises, 15447 potential breeding sites suitable to host larvae of pupae were found; of these sites18.0% contained water. Among the 2775 potential breeding sites that contained water, 452 (16.3%) were positive for larvae and/or pupae. Schools were associated with the proportionally highest number of breeding sites; 85 out of 133 (63.9%) breeding sites were positive for larvae and/or pupae in schools compared with 338 out of 2288 (14.8%) in residential premises. The odds ratio (OR) for schools and work or public sites for being infested with larvae and/or pupae was 2.77 (95% CI 1.58, 4.86), when compared to residential premises. Occupants of 80.8% of the residential premises, 54.5% of the schools and 67.7% of the work or public sites reported using preventive measures. The main prevention practices were coverage of containers and elimination of mosquito breeding places. Occupants of residential premises were much more likely to practice preventive measures than were those of non-residential premises (OR 2.23; 1.49, 3.36).ConclusionSchools and working sites were associated with the highest numbers of breeding sites and lacked preventive measures for vector control. In addition to pursuing vector control measures at residential level, public health strategies should be expanded in schools and work places.
Breeding habitats of Ae.aegypti and Ae.albopictus were studied from July 2002 to August 2003 in Kandy District, Sri Lanka. Den gue fever (DF) and dengue haemorrhagic fever (DHF) cases were identified and details of pa tients were collected in consultation with Regional Epidemiologist, Kandy. Entomological investi gations were carried out around 347 DF/DHF cases in 120 study sites, covering an area of 100. m radius around each case and including a mini mum of 100 houses per site. All possible breed ing places were examined, Aedes larvae were col lected in labelled containers using pipetting, dip ping and siphoning techniques. Larvae were iden tified in the laboratory. 884 containers positive for Ae.aegypti and Ae.albopicus were encountered around 12,470 houses. The majority (51.36%) of positive con tainers for Aedes breeding were the water stor age tanks and barrels. Water storage containers have constituted 66.66% breeding habitats of Ae.aegypti. Other important containers positive for Aedes breeding were tyres (11.88%), discarded plastic containers (11.31%), earthen pots (10.07%), and metal ware (3.17%). For all types of containers (except for roof gutters), number of containers positive for Ae.albopictus was higher than that for Ae.aegypti.
Malaria in Sri Lanka is closely associated with the river systems in the country. Construction of major dams across rivers has resulted in year-round pooling and anopheline mosquito breeding in river beds below the dams. This study was carried out to determine the larvivorous activity of fish found in river bed pools below the dams to identify the potential fish species for anopheline larval control in these areas. Fish species in five river beds below the dams, namely, Laxapana, Kotmale, Nilambe, Victoria, and Rantembe, were identified in June 2000. The larvivorous potential of the 12 fish species collected was determined in the laboratory based on the number of larvae consumed per fish within 10 min and an hour. Danio malabaricus Jerdon, Oreochromis mossambicus Peters, Oreochromis niloticus L., and Poecilia reticulata Peters consumed nine or more larvae per fish within 10 min. Aplocheilus dayi Steindachner and Rasbora daniconius Hamilton consumed nine and eight larvae, respectively, within 1 h. O. mossambicus, O. niloticus, and P. reticulata consumed 10 larvae per fish within 10 min. Despite some species having a high larvivorous potential in the laboratory, field studies are required to determine the feasibility of using these fish for anopheline mosquito control in the river bed pools below the dams.
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