Browsing by Author "Dalpadado, C.P.R.D."

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    Activity and bionomic aspects of primary and secondary vectors for dengue transmission in Gampaha district, Sri Lanka
    (University of Kelaniya, Sri Lanka, 2022) Dalpadado, C.P.R.D.
    Sri Lanka had experienced periodic dengue epidemics every two to three years for the last two decades. In this scenario, understanding bionomics aspects, and the prevalence of dengue vector species in varied settings will help to develop more accurate and focused vector control approaches. Thus, the current study is intended to elucidate the bionomics of Aedes aegypti and Ae. albopictus, in urban (Negombo, Wattala, Kelaniya), suburban (Attanagalla, Gampaha, Minuwangoda) and rural (Dompe, Meerigama, Divulapitiya) areas of the Gampaha District, Sri Lanka from April 2017 to December 2019. The effectiveness of the insecticide space spraying depends on susceptibility status and the behaviour of the targeted species, hence a part of this study included testing susceptible levels of Ae. aegypti and Ae. albopictus against malathion and deltamethrin insecticides. The study also sought to establish area-specific threshold values for determining the risk of dengue transmission based on larval indices, and a forecasting model for predicting impending dengue outbreaks within the district. Total 19,835 possible breeding habitats were investigated at 13,563 premises where Aedes larvae were identified in 11.03% of premises and 1856 habitats were positive for larvae (Ae. aegypti; 9.8%; Ae. albopictus; 90.2 %). Results showed that Ae. aegypti prefers urban locations while Ae. albopictus is the predominant vector in all spatial settings. Ae. albopictus (54.5%; n= 999) dominated the adult collection, followed by Ae. aegypti (45.5%; n= 835), with a 1:4 male to female ratio. Ae. aegypti mosquitoes demonstrated endophilic resting behaviour, whereas Ae. albopictus were exophilic (Chi-square analysis between the two species; P < 0.001). Resting places of Aedes aegypti recorded as on cloth hangings (36.9%, n=308) and under furniture (40.4%) predominantly in bedrooms (40.4%) and living rooms (24.8%) while Ae. albopictus preferred to rest on outdoor vegetation Xxix 46%(n=460). The majority (43.7 %; n=801) of Aedes mosquitoes rest 1-2 m above ground, and 34.4 % (n=399) rested 1 m or less. The host-seeking cycle of Ae. albopictus was bimodal, with morning peak occurring between 05:00 and 11:00 and afternoon peak between 14:00 and 19:00. While that of Aedes aegypti was with a minor peak between 05:00 and 09:00 and a major peak between 13:00 and 19:00. Physicochemical parameters of mosquito breeding water changed significantly across breeding categories (Kruskal—Willi’s statistics, p < 0.001) showing the change of mosquito susceptibility status. There was a strong positive association between rainfall, larval vector density, and the likelihood of high dengue incidence. When Breteau Index for Ae. aegypti (BIA) exceeds 3.00 and relative humidity exceeds 80%, an early epidemic alert is triggered while BIA > 6.0, case incidence reached an epidemic level in urban areas. In suburban areas, when BI for Ae. albopictus (BIB) > 14.0 an early epidemic alert is triggered. At the BIB > 20, case incidence reached epidemic levels even in absence of Ae. aegypti. Case incidence exceeds the epidermic level in rural areas when the BI for Ae. albopictus is 10 with a one-month latency. In conclusion, area-based entomological thresholds and rational use of insecticides can be proposed for future control of rising dengue epidemics in the Gampaha district based on vector biology/bionomic related evidence through regular monitoring.
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    Susceptibility among Dengue Vectors to Malathion and Deltamethrin Insecticides in Three Selected Medical Officer of Health (MOH) Areas in the District of Gampaha, Sri Lanka
    (International Postgraduate Research Conference 2019, Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2019) Dalpadado, C.P.R.D.; Amarasinghe, L.D.; Gunathilaka, P.A.D.H.N.
    Dengue has become the most important public health problem in Sri Lanka at present. As there is no effective vaccine or drug up to now, vector control is the main arm of disease control. Of these approaches, insecticide based control is used widely. However, excess use of chemicals and inappropriate application without determining the discriminative doses has given rise to the insecticide resistance among vector mosquitoes. Entomological surveys (Ovitap) were conducted in Negombo, Attanagalla and Dompe Medical Officer of Health (MOH) areas representing Urban, Sub urban and rural conditions, respectively from December 2016 December to June 2019. A total of 100 ovitraps each was placed outdoor and indoor in randomly followed by the collection after 5 - 7days. Eggs collected from ovitraps were reared under laboratory condition the laboratory (Temperature; 27 ± 10C: Relative Humidity 70 - 80%). The reared larvae were identified using standard taxonomic keys. Identification was further confirmed by identification of adults emerged from larvae . Adult mosquitoes were reared under optimized insectary conditions provided with sugar feeding. Batch of 140 mosquitoes from Aedes aegypti (Linnaeus) and Ae. albopictus (Skuse) was taken separately from the colony 24 hour after a sugar feeding. Each batch of mosquito was exposed to malathion (0.8%) and Deltamethrin (0.03%) insecticide susceptibility following the World Health Organization (WHO) defined procedures. The experiment setup was repeated for 2 times. Mortality and corrected morality was calculated using Abbortt’s formula after 24 hours’ exposure period. The results indicate that both dengue vectors have evolved high level of insecticide resistance to malathion (0.8%) and deltamethrin (0.03%) in the District of Gampaha except Ae. albopictus mosquitoes in rural areas. Ae. albopictus mosquitoes were found fully susceptible for 0.03% deltamethrin in Dompe (rural) MOH area and emergence of resistance (95.9%) was observed in Attanagalla (suburban) area. It was found resistant in Negombo area (83.8%) which is highly populated. Ae. albopictus mosquitoes were found fully resistant for 0.8% malathion in both urban (71.5%) and Sub urban (85.3%) areas while emergence of resistance was observed in Dompe MOH area (90.8%). Ae. aegypti was found resistance to both 0.03% deltamethrin and 0.8% malathion in Negombo area (88.1%, 53.5% respectively) and resistance was suggested for 0.03% deltamethrin in Attanagalla MOH area (91.8%) while it was found resistant for 0.8% malathion (89.8%) in the same area. Ae. aegypti was not recorded in Dompe MOH area during the study period. Since both the dengue vectors have developed resistance to WHO diagnostic discriminative doses for Malathion and deltamethrin intensity bioassays (five times and ten times of discriminative dose) are needed to be done to confirm the level of resistance in these vectors. Therefore, results highlight the requirement of continuous insecticide resistance monitoring incorporated with the surveillance and control efforts. Hence, use of evidence based discriminative doses of insecticide for each area should be vital to delay the development of resistance among natural population