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This repository contains the published and unpublished research of the Faculty of Medicine by the staff members of the faculty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 Comparative analysis of the larvicidal activity of temephos (EC50) and novaluaron (EC10) to control Anopheles stephensi in Sri Lanka(Elsevier, 2023) Jude, J.; Gunathilaka, N.; Udayanga, L.; Fernando, D.; Premarathne, P.; Wickremasinghe, R.; Abeyewickreme, W.Background: Anopheles stephensi was first recorded in the coastal area of Mannar District, Sri Lanka, in December 2016. Since then, this vector has been isolated from other districts in the Northern and Eastern Provinces of Sri Lanka. Chemical control is the main arm of vector control that can be used to reduce the vector densities within a short period. Thus, the present study aimed at evaluating the efficacy of using selected insecticides for the control of An. stephensi larvae. Method: The third and fourth instar larval stages of An. stephensi (F2 generation) of field mosquitoes that were caught using cattle baited net trap collections from Columbuthurai, Kurunagar, and Navanthurai areas in Jaffna District, Sri Lanka, were obtained from the laboratory colony established at Jaffna. Batches of 100 larvae were taken for experiments and introduced separately to a concentration series of temephos and novaluron (0.04-400 ppm). A control test was also performed at each setup without introducing insecticides. The mortality rates of An. stephensi larvae exposed to different concentrations of larvicides were recorded at 1, 24 and 48-h intervals. The experiment was replicated five times at individual concentrations for each selected chemical. Data were analyzed using the General Linear Model (GLM) and Probit analysis. Results: The highest mortality rate (100%) at a 1-h exposure period was observed from temephos at >100 ppm. The mortality 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 both temephos and novaluron even at 0.04 ppm. Conclusion: Both temephos and novaluron reported 100% mortality rates in An. stephensi larvae at 1-h and 24-h exposure periods. Based on the findings, temephos and novaluron can be recommended as effective larvicides for chemical-based control of An. stephensi in Jaffna, Sri Lanka. Further, it is recommended to conduct a field-based study, where habitat types and water quality are highly heterogeneous and may affect the residual activity.Item Biology, bionomics and life-table studies of Anopheles stephensi (Diptera: Culicidae) in Sri Lanka and estimating the vectorial potential using mathematical approximations(Elsevier, 2023) Jude, J.; Gunathilaka, N.; Udayanaga, L.; Fernando, D.; Premarathne, P.; Wickremasinghe, R.; Abeyewickreme, W.Background: Anopheles stephensi is an invasive mosquito in Sri Lanka that can potentially transmit malaria. The transmission intensity is linked with biology, bionomic and behavioral aspects of a vector that are associated with the Vectorial Capacity (VC). However, the influence of larval conditions eventually affects the vectorial potential of An. stephensi are not well understood. Methods: A colony of An. stephensi was established at the Regional Centre of the Open University of Sri Lanka, Jaffna District. The colony was maintained under confined conditions according to standard protocols. Biotypes of An. stephensi were characterized by referring to the number of egg ridges. Information on (a) biological aspects of eggs (duration for egg hatching, egg development and hatchability), (b) larval development time, larval survivorship pupation success, resting depth of larvae), (c) pupae (adult emergence rate, average time for adult emergence) and (d) adults (biting frequency, mating success gonotrophic cycle, fecundity, duration for egg-laying, percentage of sexes, adult survival/longevity) were evaluated under life-table analysis. Further, selected morphometric characters of each life cycle stage were recorded from the eggs (length and breadth), larvae (head length, width of head, length of thorax, width of thorax, length of abdomen, width of abdomen, and the total length of larvae), pupae (cephalothoracic length and width) and adults (length & width of wing, thorax and abdomen). The VC was calculated using a mathematical-based approach. Descriptive statistics, General Linear Model (GLM) and independent-sample t-test were used for the statistical analysis. Results: All three biotypes were identified based on egg morphology. Mysorensis biotype (47%; n = 470) was predominant followed by type (38.1%; n = 381) and intermediate (14.9%; n = 149). The mean egg length (F(2,997) = 3.56; P = 0.029) and breadth (F(2,997) = 4.57; P = 0.011) denoted significant differences among the three biotypes. The mating success of females observed 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 required for larval development and 30.3 ± 0.14 h were spent in the 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. Conclusions: The type biotype, which is an effective vector in the Indian subcontinent is present in Sri Lanka. According to the mathematical approximation, An. stephensi found locally has a vectorial capacity of over 18. Therefore, this study warrants the health authorities and vector control programmes to continue the entomological surveys, monitoring of vector densities and implementing appropriate vector control interventions based on biology and bionomic information of vectors.Item Developmental responses and survival of Anopheles stephensi larval stages at different salinity levels(Royal Society of Tropical Medicine and Hygiene, 2022) Jude, J.; Gunathilaka, N.; Udayanaga, L.; Fernando, D.; Premarathne, P.; Wickremasinghe, R.; Abeyewickreme, W.BACKGROUND: Anopheles stephensi is a newly invaded vector in Sri Lanka. It has been identified in coastal areas in the northern and eastern parts of the country and evidences the ability to breed in brackish water environments. METHODS: Laboratory investigations were conducted with batches of 100 first and third instar larvae exposed to a salinity gradient (0-40 ppt). Survival rates at 1 h, 24 h and until pupation were recorded for first and third instar larvae at different salinity levels. The experiment was repeated four times for both instars. Data were analysed using the general linear model and probit analysis. RESULTS: Significant variations in adult emergence were observed from both larval stages at different salinity levels (p<0.05). The highest pupation rates were observed at 2.5 ppt salinity. The survival rate of first instar larvae after 24 h of salinity exposure was >80% up to 12.5 ppt, while 100% mortality was observed for from the ≥25 ppt level of salinity. More than 90% of the third instar larvae pupated from salinity levels <15 ppt. The lowest survival rate was reported as 15.8±2.47% at 25 ppt. CONCLUSIONS: This indicates a high potential of increasing density of A. stephensi in coastal ecosystems in lagoons and other saline water bodies. Hence it is high time to redesign vector control interventions for vector breeding in coastal ecosystems.Item Breeding habitat distribution of medically important mosquitoes in Kurunegala, Gampaha, Kegalle, and Kandy districts of Sri Lanka and potential risk for disease transmission: A Cross-sectional study(Hindawi Pub. Corp., 2020) Ranasinghe, K.; Gunathilaka, N.; Amarasinghe, D.; Udayanga, L.ABSTRACT: Some arbovirus infections, especially dengue, have increased rapidly over the last few decades in Sri Lanka. Prevalence and distribution of different mosquito species have been limitedly documented, which remains grossly inadequate in providing evidence for potential health risks. In this study, the diversity and species composition of mosquitoes in four selected districts in Sri Lanka (Kurunegala, Gampaha, Kegalle, and Kandy) were investigated. Entomological surveys were conducted from a total of 160 temporary and permanent mosquito breeding habitats identified in the study area from June 2017 to October 2018. Mosquito immature stages were sampled using standard dipping, siphoning, or pipetting methods and identified up to the species level. Percentage relative abundance and habitat characteristics such as species richness, dominance, and Shannon-Weiner diversity were calculated for each surveyed habitat type. Associations between co-occurring species were estimated by Hulbert's coefficient of interspecific association (C8). A total of 4663 mosquito larvae belonging to seven genera and fifteen species of mosquitoes were collected. The relative distribution of mosquito species differed significantly among the four studied districts (X 2 = 143.248; df = 33; P < 0.001). According to Kruskal-Wallis statistics (P < 0.05 at 95% of significance), all diversity indices for immature stages of medically important mosquitoes varied significantly across different breeding sites. Paddy fields had the significantly highest species richness of 4.0 ± 2.82. The coefficients of interspecific association among all the recorded medically important vector mosquitoes were found negative during the present study. The findings of the current study would be useful to identify the entomological potential for disease transmission and facilitate the implementation of appropriate vector control interventions. This would ultimately provide an avenue to improve the personal skills of health staff rather than limiting their knowledge to specified disease vectors, under which the control program is concerned.Item Illustrated key to the adult female Anopheles (Diptera: Culicidae) mosquitoes of Sri Lanka(Springer, 2017) Gunathilaka, N.The identification of adult female anopheline mosquitoes is an important aspect in malaria surveillance and control strategy throughout the world, and taxonomic keys are being regularly revised and updated as new information becomes available. However, the currently available key to the anophelines of Sri Lanka is of limited use, because they were published more than 25 years ago. This paper presents an illustrated key for the identification of 23 adult female Anopheles mosquitoes which are currently recognized as local anopheline species in Sri Lanka.Item Appearance of Anopheles jeyporiensis James from Sri Lanka; a new species to the mosquito checklist(The Japan Society of Medical Entomology and Zoology, 2015) Gunathilaka, N.; Abeyewickreme, W.; Hapugoda, M.; Wickremasinghe, A.R.Previous records of Sri Lankan Anopheles were most imperfect, and even the number and names of the species present were very doubtful. There was no systematic study conducted for Sri Lankan adult anophelines since 1990. Therefore, the objective of this study was to explore the species abundance and morphological variations of anopheline mosquitoes in Sri Lanka. Entomological surveys were conducted on a monthly basis from June 2010 to December 2013 in Trincomalee District, using five entomological techniques. Entomological surveys identified a total of 131,804 mosquito specimens belong to 18 anopheline species. One of which was An. jeyporiensis, a species that was not in the checklist in Sri Lanka. Its basic morphological features are similar to the members in Myzomyia series under the subgenus Cellia. Following characteristics were used to confirm the species as An. jeyporiensis; Centre of the scutum covered with short oblong white scales extending back to scutellum; Vein R 1 usually with accessory pale spot on preapical dark (PD) area; Foretarsomere 1 with apical pale band nearly 2.0 width of tarsomere diameter.Item Entomological investigations on malaria vectors in some war-torn areas in the Trincomalee district of Sri lanka after settlement of 30-year civil disturbance(Hindawi Publishing Corporation, 2015) Gunathilaka, N.; Hapugoda, M.; Abeyewickreme, W.; Wickremasinghe, R.Background. Malaria was an endemic problem in Trincomalee District, Eastern Province of Sri Lanka. Very few recent data concerning Anopheles are available which transmit malaria. Therefore, the aim of this study is to identify various Anopheles species and the dynamics of anophelines including malaria vectors in Trincomalee District for effective vector control under the current malaria elimination program embarked in the country. Method. Entomological surveys were conducted on a monthly basis, using five entomological techniques, namely, indoor hand collection (HC), window trap collection (WTC), cattle-baited net collection (CBNC), and cattle-baited hut collection (CBHC) from June 2010 to June 2012 in 32 study areas under five entomological sentinel sites. Results. Seventeen anopheline species were encountered, of which Anopheles subpictus was the predominant species in all sampling methods. It is noted that A. culicifacies and A. subpictus have adapted to breed in polluted water in urban settings which may cause serious implications on the epidemiology of malaria in the country. Conclusions. It is important to determine the abundance, biology, distribution, and relationship with climatic factors of main and secondary malaria vectors in Sri Lanka in order to initiate evidence based controlling programs under the current malaria elimination program in Sri Lanka.Item Revised morphological identification key to the larval anopheline (Diptera: Culicidae) of Sri Lanka(Asian Pacific Tropical Medicine Press, China, 2014) Gunathilaka, N.; Fernando, T.; Hapugoda, M.; Abeyewickreme, W.; Wickremasinghe, R.OBJECTIVE: To revise morphological identification keys to the anophelines in Sri Lanka. METHOD: Samples were collected from selected entomological sites in different districts in the country. Stage III and IV larvae were identified under a light microscope with an objective (×10) using standard larval keys developed for Sri Lankan anophelines. Key larval characters were recorded for each species based on original observations and previous usage in literature. RESULTS: This manuscript describes an illustrated key for the identification of 22 of 23 mosquitoes which are currently recognized as local anopheline species in Sri Lanka, as a guide to workers engaged in malaria surveillance and control in the country. CONCLUSIONS: Revised morphological keys to the larval of these species may be helpful in easy and accurate identification at the field level.