Theses - Faculty of Medicine
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Item Bionomics and control effects of anopheles stephensi in Mannar and Jaffna districts of Sri Lanka(University of Kelaniya, Sri Lanka, 2023) Jude, P.J.BACKGROUND: Sri Lanka was declared as a country that eliminated malaria disease in 2016 by the World Health Organization. Recent report of Anopheles stephensi as an invasive vector in the northern part of Sri Lanka is one of the challenges to maintain themalaria free states in the country. METHODS: Entomological surveys were conducted at three selected localities in Jaffna and Mannar Districts of Sri Lanka from January 2019 to January 2020 using three entomological techniques. Detailed biology and life cycle related information namely were assessed. Further, effectiveness of insecticide based control efforts (novaluron andtemephos) and application of larvivorous fish Poecilia reticulata were evaluated under laboratory set-up. The Vectorial Capacity (VC) was calculated using a mathematical-based approach. RESULTS: According to the egg morphology, Mysorensis biotype (47%) was the predominant followed by type (38.1%) and intermediate (14.9%). The mating success was 80.7 + 4.45%. The mean hatching period was 1.9 + 0.03 days, with a hatching rate of 86.2 + 0.77%. Overall, 8.0 + 0.14 days were irequired for larval development and 30.3 + 0.14 h were spent in \4e pupal stage. The pupation success was 94.5 + 0.37%, and the majority were males (53.1 + 0.73%). The mean fecundity was 106.5 + 6.38 eggs and a gonotrophic cycle of 3.4 + 0.06 days. The female survival rate was 43.2 + 2.4%, with a mean biting frequency of 66.6 + 3.5%. The average VC of adult An. stephensi was estimated to be 18.7. Significant variations in adult emergence were observed from both larval stages at different salinity levels (P < 0.05). The lowest survival rate was reported as 15.8 2.47% at 25 ppt. The highest mortality rate (100%) at a 1-hour exposure period was observed from temephos at >100 ppm. The nortality rates varied significantly for different concentrations and larvicides (P < 0.05). At 24-h of the exposure period, the 100% mortality of An. stephensi larvae were observed from Bi h temephos and novaluron even at 0.04 ppm. In larvivorous fish study, the survival rate of P. reticulata in both Jaffna and Mannar Districts was significantly different at different chlorine levels (P80% even at 0.75 mg/L. At the 24-hours, the mean survival rates of 70.0+ 5.8% (Jaffna) and 81.7 + 4(Mannar) were observed at 0.75 mg/L. At 48 hours, the fish survived only at 0.75 mg/Lindicating a higher survival rate from Mannar (81.7 + 4.4%), while the fish from Jaffna denoted 70.0 + 5.8% of survival. CONCLUSIONS: The type biotype, which: is an effective vector in the Indian subcontinent is present in Sri Lanka. Anopheles stephensi indicated a vectorial capacity of over 18. There is a high potential of increasing density of An. stephensi in coastal ecosystems. The temephos and novaluron can be recommended as effective larvicides for chemical-based control of An. stephensi in Jaffna, Sri Lanka. The fish captured from Mannar demonstrated a higher tolerance to chlorine levels.Item 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.