Graduate Studies
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Item 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 populationItem A Statistical Approach to Define Thresholds for Dengue Epidemic Management in Akurana Medical Officer of Health Area, Kandy District of Sri Lanka(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Udayanga, N.W.B.A.L.; Gunathilaka, P.A.D.H.N.; Iqbal, M.C.M.; Fernando, M.A.S.T.; Abeyewickreme, W.Stegomyia indices, namely; Premise Index (PI), Breteau Index (BI) and Container Index (CI) are used forvector management approaches in Sri Lanka. Properly defined threshold values for larval indices are of higher importance to provide forecasts on dengue epidemics and also for effective larval management of dengue vectors. However, such critical thresholds are poorly defined for Sri Lanka. The present study aimed to define threshold values forabove larval indices for dengue epidemic management in the Akurana Medical Officer of Health (MOH) in the Kandy District. Larval surveys were conducted on a monthly basis from January, 2016 to June, 2018. Four larval indices, namely BI for Aedesaegypti (BIA) and Aedesalbopictus (BIB), PI and CI were calculated. Further, monthly larval indices of AkuranaMOH area from January, 2012 to December, 2015, were obtained from the MOH office, along with monthly reported dengue cases for the entire study period. Receiver Operating Characteristic (ROC) curves in SPSS (version 23) were used to assess the discriminative power of the larval indices in determiningdengue epidemics and thresholds based on larval indices. As indicated by the area of ROC curve (AUC), the BIA (0.661) and PI (0.637) were having a notable discriminative power to forecast dengue epidemics at a two-month lag period. Both BIB (0.397) and CI (0.526) were non-informative influencers at one and two-month lag periods. The BIA and PI were better predictors of dengue incidence than BIB and CI. Based on the ROC curve, three risk thresholds were defined for BIA as Low Risk (BIA≤2.1), Moderate Risk (3.9≤BIA<4.85), and High Risk (BIA≥4.85), with respect to Ae. aegypti. According to the PI, thresholds were defined as Low Risk (PI≤6.2), Moderate Risk (7.7≤ PI<9.9), and High Risk (PI≥ 9.9). Threshold values defined for BI of Ae. aegypti and PI, could be recommended to be considered in implementing vector control efforts in the above study area for effective dengue epidemic management, through pre planned entomological management of dengue vectors.Item Role of Larval Indices on the Incidence of Dengue Epidemics in Akurana, Medical Officer of Health (MOH) Area, Kandy.(In: Proceedings of the International Postgraduate Research Conference 2017 (IPRC – 2017), Faculty of Graduate Studies, University of Kelaniya, Sri Lanka., 2017) Udayanga, N.W.B.A.L.; Gunathilaka, P.A.D.H.N.; Iqbal, M.C.M.; Fernando, M.A.S.T.; Abeyewickreme, W.As in many other Asian countries, vector control entities in Sri Lanka also depend upon larval indices as the major driving factor of routine entomological surveillance and management of dengue vectors. However, studies aimed at defining the role of larval indices, which reflect the population dynamics of dengue vectors, on the incidence of dengue outbreaks are limited. This is mainly due to restrictions in long-term vector density related data. Hence, the current study attempts to evaluate the role of larval indices on the incidence of dengue epidemics in Akurana, Medical Officer of Health (MOH) area.Item Optimization of Critical Threshold Values for Aedes Mosquitoes based on Breteau Index in Kandy District of Sri Lanka.(In: Proceedings of the International Postgraduate Research Conference 2017 (IPRC – 2017), Faculty of Graduate Studies, University of Kelaniya, Sri Lanka., 2017) Udayanga, N.W.B.A.L.; Gunathilaka, P.A.D.H.N.; Iqbal, M.C.M.; Kusumawathie, P.H.D.; Abeyewickreme, W.Many countries, including Sri Lanka, mainly depend upon Stegomyia indices,such as Premise Index (PI), Breteau Index (BI),Container Index (CI), and Pupal Index (PI) for routine entomological surveillance of dengue. Among them, BI remain as the most widely used larval index for vector management prior to and during epidemic incidences. Properly defined threshold values for BI are of essence, to assist the prediction of dengue epidemics and as a leading indicator for vector control. However, Sri Lanka still lacks effective thresholds for BI to initiate and drive dengue vector management activities. Hence, the present study attempts to define threshold values for BI based on an empirical modelling approach for the Kandy District of Sri Lanka.Item Eliminating female Aedes mosquitoes by spiking blood meals with toxicants as a sex separation method in the context of the sterile insect technique and Incompatible Insect Technique(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Ranathunga, R.M.T.B.; Gunathilaka, P.A.D.H.N.; Udayanga, N.W.B.A.L.; Wijegunawardena, N.D.A.; Abeyewickreme, W.Ivermectin and spinosad have longevity reducing effects in several insect species, including disease transmitting mosquitoes after feeding blood contaminated with above toxicants on hosts. Therefore, this approach could play an enormous role in mosquito control operations by its use in the female elimination process during mass-rearing, enabling the release of only sterile males in the context of the sterile insect technique (SIT) and incompatible insect technique (IIT) with Wolbachia bacterium. Blood meals of cattle origin were spiked with diffeerenct concentrations (2, 4, 6, 8 and 10 ppm) of Ivermectin (Ivotec, 1% w/v) and Spinosad (Spinosyn, 12% w/v) and offered to a batch of adult Ae. aegypti (n = 300) and Ae. albopictus (n = 300) having 1:1 sex ratio in order to obtain an optimal dose for quick and total female elimination. After 24 hours all remaining females and males were aspirated out and transferred in to new cages separately. An additional blood meal with the initially fed concentrations of ivermectin and spinosad was provided after 24 hours, followed by a 48-hour observation of mortality. This experiment was repeated by feeding cattle blood containing a mixture of ivermectin and spinosad in 1:1 ratio from each concentration. Spiked blood with 8 ppm ivermectin and spinosad killed all the fed females of Ae aegypti and Ae. abopictus within 24 to 48 hours. It was observed that the number of fed females gradually increased, when decreasing the toxicity in combination of ivermectin and spinosad (1:1) in blood for both species. Male mortality did not show any significant differences during the study. Mixed feeding of blood with 8 ppm ivermectin and 8 ppm spinosad have shown as the viable treatment to eliminate female Ae aegypti and Ae. abopictus from laboratory colonies.Item Prevalence of dengue vector breeding habitats among selected Schools in Gampaha District of Sri Lanka(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Radhika, N.M.L.; Gunathilaka, P.A.D.H.N.; Kasturiratne, K.T.A.A.; Abeyewickreme, W.Aedes aegypti and Aedes albopictus are the vectors responsible for the transmission of dengue viruses in Sri Lanka. Gampaha District has been ranked as the second most Dengue affected area. Recently, health authorities have identified that over 54 percent of schools have dengue mosquito breeding sites. However, the entomological information on the dengue vectors in School premises are not available. Therefore, the present study was carried out to identify the different breeding sites of dengue vector mosquitoes within school premises of randomly selected schools in Gampaha District of Sri Lanka. The premises of the selected schools (n= 34) were surveyed from May to October in 2016 for the availability of potential breeding habitats and the presence of vector breeding through entomological surveys. Collected vectors were identified morphologically and categorized inn to species level. All data on breeding habitats and number of vectors identified were recorded. According to survey, out of 34 schools surveyed; infested water-holding containers by Ae. albopictus were observed at 16 schools (47, 05%). Tree holes (Bridelia retusa tree), leaf axils of banana tree and fallen leaves were observed as natural breeding sites while, discarded plastic food containers plastic paint containers, broken pet bottles, tire marks on the ground, water retaining flower pots and plastic barrels were observed as artificial breeding sites. Breeding of Ae. aegypti was not identified among the school premises surveyed. Improper management of solid waste has affected positively in creating suitable habitats for vector breeding. Therefore, continuous monitoring of dengue vector breeding habitats and school based vector controlling interventions should be implemented through proper awareness and active participation for eliminating breeding habitats.Item Evaluation the Oviposition Behaviour of Aedes Aegypti and Ae. Albopictus Mosquitoes; Main and Secondary Vector for Dengue Transmission in Sri Lanka under Laboratory Conditions(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Gunathilaka, P.A.D.H.N.; Ranathunga, R.M.T.B.; Udayanga, N.W.B.A.L.; Abeyewickreme, W.Studies on the oviposition behavior of Aedes albopictus and Ae. aegypti are critical for effective controlling of dengue vector breeding. However, less attention has been drawn on such aspects of vector biology and bionomics in Sri Lanka. Therefore, the objective of the current study was to evaluate the oviposition behavior of dengue vectors under laboratory conditions. Ovitraps with different sizes, colours, sources of water, sodium chloride (NaCl) concentration (0.2, 0.5, 1, 2 and 3%) and presence and absence of larvae were kept within separate cages of batches of 1000 Ae. albopictus and Ae. aegypti with (1:1, male: female ratio). Female mosquitoes were allowed to lay eggs and the number of eggs laid in different ovitraps were enumerated. ANOVA and cluster analysis were used to investigate the significance in the variations among oviposition behaviours. The mean number of eggs laid by both Ae. albopictus and Ae. aegypti increased with the increasing size of the ovitraps. Ae. albopictus indicated the highest mean number of eggs in 0.2% of NaCl than that of distilled water, while the egg laying preference reduced with the increasing salinity for both species. Drain water with low dissolved oxygen level (0.43 ± 0.12 mg/l) was the preferred water source for both species and indicated a significantly high oviposition rate in ovitraps with larvae. Black colour ovitraps attracted the majority of the gravid females, while white was least preferred. There were no significant variations among oviposition behaviors of Ae. albopictus and Ae. aegypti under laboratory conditions. Back coloured ovitraps were the preferred breeding place.