Medicine
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This repository contains the published and unpublished research of the Faculty of Medicine by the staff members of the faculty
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Item Bionomic aspects of dengue vectors Aedes aegypti and Aedes albopictus at domestic settings in urban, suburban and rural areas in Gampaha District, Western Province of Sri Lanka(BioMed Central, London, 2022) Dalpadado, R.; Amarasinghe, D.; Gunathilaka, N.; Ariyarathna, N.Background: The lack of information on behavioural patterns of Aedes aegypti and Aedes albopictus has become a significant limitation in vector control and disease management programmes. Therefore, the current study was focused on determining some bionomics aspects: breeding, resting, host-seeking and feeding preferences of Ae. aegypti and Ae. albopictus in Sri Lanka. Methods: Larval and adult surveys were conducted from April 2017 to April 2019 monthly in six selected Medical Officer of Health (MOH) areas in Gampaha Distinct, Western province, Sri Lanka, representing urban, suburban and rural settings. Resting preferences of adult mosquitoes were observed from indoor and outdoor places using a Prockopack aspirator. The information on resting height, surface, material and locality was recorded. Human-baited double-net traps were used to determine the host-seeking time of Aedes mosquitoes. Statistical differences in the spatial distribution of mosquitoes in selected MOH areas and prevalence of vectors were analysed using general linear model (GLM). A chi-square test was used to analyse the resting behaviour. Results: Total of 19,835 potential breeding sites were examined at 13,563 premises, and 18.5% (n = 1856) were positive for Aedes larvae. Distribution of Ae. aegypti and Ae. albopictus was statistically significant at species level (df = 1; F = 137.134; P < 0.05 GLM) and study setting (df = 2; F = 8.125; P < 0.05). Aedes aegypti breeding was found mainly in temporary removals (18.8%; n = 34), discarded non-degradables (12.15%; n = 22) and tyres (9.95%; n = 18). Natural (14.7%; n = 246) and temporary removals (13.6%; n = 227) and discarded non-reusable items were the key ovipositing sites for Ae. albopictus. In the adult mosquito survey, the majority was comprised of Ae. albopictus (54.5%; n = 999), which denoted exophilic nature (90.8%; n = 758), and 45.5% (n = 835) represented by Ae. aegypti mosquitoes who were mainly endophilic (84.3%; n = 842). Aedes aegypti rested on cloth hangings and curtains, followed by the furniture, while Aedes albopictus was predominant in outdoor vegetation. In both vectors, biting patterns denoted a typical diurnal pattern with two peaks of host-seeking and biting activity in the morning and afternoon. Conclusions: The majority (80%) of the larval habitats were artificial containers. The use of larvicides for vector control as the prominent measure is questionable since applying these chemicals may target only 20% of the total breeding grounds, which are permanent. The resting places of adult mosquitoes are mainly indoors. Therefore, using thermal space spraying of insecticide may not be appropriate, and indoor residual spraying is recommended as a suitable intervention to target adult mosquitoes. This study warrants a holistic vector control approach for all medically important mosquitoes and insects, ensuring the rational use of finance and resources.Item Diversity of midgut bacteria in larvae and females of Aedes aegypti and Aedes albopictus from Gampaha District, Sri Lanka(BioMed Central, 2021) Ranasinghe, K.; Gunathilaka, N.; Amarasinghe, D.; Rodrigo, W.; Udayanga, L.BACKGROUND: The midgut microbiota of mosquitoes maintain basal immune activity and immune priming. In recent years, scientists have focused on the use of microbial communities for vector control interventions. In the present study, the midgut bacteria of larvae and adults of Aedes aegypti and Ae. albopictus were assessed using both field-collected and laboratory-reared mosquitoes from Sri Lanka. METHODS: Adults and larvae of Ae. aegypti and Ae. albopictus were collected from three selected areas in Gampaha Medical Officer of Health area, Gampaha District, Western Province, Sri Lanka. Bacterial colonies isolated from mosquito midgut dissections were identified by PCR amplification and sequencing of partial 16S rRNA gene fragments. RESULTS: Adults and larvae of Ae. aegypti and Ae. albopictus harbored 25 bacterial species. Bacillus endophyticus and Pantoea dispersa were found more frequently in field-collected Ae. aegypti and Ae. albopictus adults, respectively. The midgut bacteria of Ae. aegypti and Ae. albopictus adults (X2 = 556.167, df = 72, P < 0.001) and larvae (X2 = 633.11, df = 66, P < 0.001) were significantly different. There was a significant difference among the bacterial communities between field-collected adults (X2 = 48.974, df = 10, P < 0.001) and larvae (X2 = 84.981, df = 10, P < 0.001). Lysinibacillus sphaericus was a common species in adults and larvae of laboratory-reared Ae. aegypti. Only P. dispersa occurred in the field-collected adults of Ae. aegypti and Ae. albopictus. Species belonging to genera Terribacillus, Lysinibacillus, Agromyces and Kocuria were recorded from Aedes mosquitoes, in accordance with previously reported results. CONCLUSIONS: This study generated a comprehensive database on the culturable bacterial community found in the midgut of field-collected (Ae. aegypti and Ae. albopictus) and laboratory-reared (Ae. aegypti) mosquito larvae and adults from Sri Lanka. Data confirm that the midgut bacterial diversity in the studied mosquitoes varies according to species, developmental stage and strain (field vs laboratory). KEYWORDS: 16S rRNA gene; Aedes; Bacteria; Diversity; Midgut; Mosquitoes.Item Biocontrol potential of six locally available fish species as predators of Aedes aegypti in Sri Lanka(Elsevier Ltd, 2021) Ranathunge, T.; Kusumawathie, P.H.D.; Abeyewickreme, W.; Udayanga, L.; Fernando, T.; Hapugoda, M.ABSTRACT: This study was conducted to evaluate the potential of six locally abundant fish species to control Aedes mosquito larvae and thereby manage dengue epidemics in a sustainable, cost-effective and environmentally friendly manner. The biocontrol efficacy of six larvivorous fish species, namely, Poecilia reticulata, Rasbora daniconius, Aplocheilus dayi, Oriochromis mossambicus, O. niloticus and Puntius bimaculatus, was evaluated under laboratory and field conditions. Five size-matched fish (of the same species) were introduced into separate tanks (replicates) containing 2 L of dechlorinated water and 200 third instar larvae of Aedes aegypti (L.). The number of larvae consumed by each fish species was recorded at three-hour intervals for 24 h. Acclimatized fish were introduced into a total of eighteen artificial breeding habitats located in the Gampola Medical Officer of Health (MOH) area at the species level with three replications. In addition, three breeding sites without fish were monitored as controls. Aedes larvae were monitored by dipping and siphoning methods in each breeding habitat at weekly intervals for three months and the number of fish surviving in each habitat was tallied. Over 24 h under laboratory conditions, O. mossambicus showed the highest predation rate, consuming 320.2 ± 14.5 larvae per day, with a predatory efficiency of 87.5 ± 3.5%. In comparison, O. niloticus consumed 264.6 ± 12.2 larvae per day with consumption efficiciency of 78.1 ± 3.7%, whereas R. daniconius had the lowest larval consumption (33.2 ± 2.7 larvae per day) and predatory efficiency (33.2 ± 3.2%). Over 12 weeks of observation under field conditions, breeding sites with Ap. dayi had the lowest Aedes larval counts, followed by Po. reticulata. Considering predation efficiency and survival under field conditions, Ap. dayi and Po. reticulata were considered to be the best potential candidates for biological control of Ae. aegypti. Further studies under field settings are warranted to evaluate the survival and predatory potential of the selected candidates under more varied environmental conditions.