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This repository contains the published and unpublished research of the Faculty of Medicine by the staff members of the faculty

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Larvicidal activity of the pericarp extract of Garcinia mangostana against dengue vector Aedes aegypti in Sri Lanka
(Wolters Kluwer Medknow Publications, 2022) Gunathilaka, N.; Wijebandara, Y.; Amerasinghe, D.; Udayanga, L.; Muhandiramlage, T.P.
Objective: To assess the larvicidal activity of mangosteen (Garcinia mangostana) against larval stages of Aedes aegypti mosquitoes. Methods: A crude extract was prepared in ethanol from powdered mangosteen pericarps. A concentration gradient (0.01-4.92 g/L) was prepared from the stock solution. Seven batches of 25 third instar larvae of Aedes aegypti were used for larval bioassays. Larval mortality rates were observed after one and 24 hours. Cholesterol and total lipid contents in 20 randomly selected dead larvae at each trial were assessed by colorimetric method. The experimental setup was repeated five times. The General Linear Model and Probit analysis were used to evaluate the relationship of mortality with cholesterol level, total lipid level and cholesterol to total lipid ratio. Results: The percentage mortalities significantly varied with different concentrations (F7,32=385.737; P<0.001). The LC50 and LC99 values were (0.041 ± 0.006) g/L and (10.616 ± 1.758) g/L, respectively after 24 hours. There was no mortality recorded within the one-hour exposure time. Only the cholesterol content (F5,24=173.245; P<0.001) in larvae exposed to different concentrations denoted a significantly decreasing trend within 24-hour exposure. Larvae that were exposed to the lowest concentration (0.55 g/L) showed a higher cholesterol level (22.67 ± 1.33) µg. Conclusions: The Garcinia mangostana extract acts as an effective sterol carrier protein inhibitor that inhibits cholesterol uptake in Aedes aegypti mosquitoes. Hence, it could be explored for use as a key source for the development of an environment-friendly plantbased larvicide.
Human health importance zoonotic gastrointestinal helminths and ectoparasites among stray dogs in Galle District, Sri Lanka
(Department of Biosystems Engineering of the Faculty of Agriculture & Plantation Management Wayamba University, 2021) Rathnayaka, S.; Gunathilaka, N.; Udayanga, L.
BACKGROUND: A notably high stray and semi domesticated dog population exist in close proximity to humans in Sri Lanka. However, the prevalence of gastrointestinal and ecto-parasites among these stray dog population has been limitedly studied. Therefore, the present investigation focused on zoonotic potential among stray dog community in Sri Lanka. METHODS: A total of 110 stray dogs randomly captured from the Galle District of Sri Lanka during May to July 2018 was considered for the study. Freshly voided fecal samples were obtained. Ectoparasites were collected using a lose comb and stored in an alcohol solution. Presence of major gastrointestinal and ectoparasitic species were investigated using standard microscopic methods. The Chi-square test of independence was used for statistical analysis. RESULTS: The highest egg count as Eggs per Gram (EPG) were detected from A. caninum (264.65 + 86.02 EPG), followed by T. canis (58.38 + 7.22 EPG) and E. vermicularis (22.70 + 5.70 EPG). Approximately one third of the stray dog population (29.1%; n= 32) indicated ectoparasitic infestations, dominated by Rhipicephalus sanguineus (40.9%; n=45), Ctenocephalides canis (23.6%; n=26) and Ixodes scapularis (19.1%; n=21). The results of the Chi-square test of independence denoted that there was a significant difference on the prevalence of helminthic parasites, among male and female stray dog populations (χ2= 15.19, df = 7, P = 0.03). CONCLUSIONS: The present study revealed the potential risk on human health by intestinal helminthic and ectoparasites among stray dog populations. Hence, better understanding of such diseases and their control is essential.
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.
Development of an alternative low-cost larval diet for mass rearing of Aedes aegypti mosquitoes
(Hindawi Publishing, 2020) Senevirathna, U.; Udayanga, L.; Ganehiarachchi, G.A.S.M.; Hapugoda, M.; Ranathunge, T.; Gunawardene, N.S.
BACKGROUND: Aedes aegypti is a major vector of arboviruses that may be controlled on an area-wide basis, using novel approaches such as Sterile Insect Technique (SIT) and Incompatible Insect Technique (IIT). Larval diet is a critical factor to be considered in mass rearing of Aedes mosquitoes for SIT and IIT programs. Therefore, the current study is aimed at evaluating the effects of two novel diets developed from dry fish powder on the growth and development of immature stages and adult fitness-related characteristics of Ae. aegypti in Sri Lanka. METHOD: Three batches of the first instar Ae. aegypti larva, each containing 250 larvae, were exposed to three different larval diets as standard dry fish powder (D1), dry fish powder meal and brewer’s yeast (D2), and International Atomic Energy Agency- (IAEA-) recommended diet (D3), separately. Morphometric and developmental parameters of the 4th instar larvae, pupae, and adult mosquitoes reared under different dietary treatments were measured. The entire experimental setup was replicated thrice. A General Linear Model (GLM) in the form of two-way ANOVA was used for the statistical analysis. RESULTS: Significant diet-based variations were observed in the head length, head width, thoracic length, thoracic width, abdominal length, abdominal width, and total length (; ) of Ae. aegypti larvae. The highest pupation success and the larval size were observed from the larvae fed the D2 diet, while the lowest was reported from D1. All adult morphometric parameters of adult male and female Ae. aegypti mosquitoes also denoted significant dietary variations, reporting the best-sized adults from the D2 diet (; ). Further, significantly higher fecundity and male longevity were also shown by the adult Ae. aegypti (; ) mosquitoes reared under diet D2. CONCLUSION: Based on all the growth and developmental parameters, the D2 diet tends to perform similar to the IAEA-recommended diet in mass rearing of Ae. aegypti mosquitoes, while being more inexpensive. Therefore, larval diet D2 could be suggested as the ideal diet for mass rearing of Ae. aegypti for IIT and SIT-based vector control in Sri Lanka.
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.
Larvicidal potential of five selected Dragonfly Nymphs in Sri Lanka over aedes aegypti (Linnaeus) larvae under laboratory settings.
(Hindawi Pub. Co., 2018) Samanmali, C.; Udayanga, L.; Ranathunge, T.; Perera, S.J.; Hapugoda, M.; Weliwitiya, C.
INTRODUCTION: Limitations in breeding source reduction practices, development of insecticide resistance in mosquitoes, and ill effects of chemical controlling methods on human and ecosystem health have motivated Sri Lankan authorities working for dengue control to seek for alternative, ecofriendly, and sustainable approaches for controlling of Aedes vectors, to manage dengue epidemics. The present study attempted to investigate the predation efficiency of locally available dragonfly nymphs over Aedes aegypti under laboratory conditions, aiming to evaluate the potential of using dragonflies as biocontrol agents against dengue. METHODS: Nymphal stages of five locally abundant dragonfly species were collected from different stagnated water bodies in Belihuloya area. After morphological identification, a well grown individual of each species was starved for 12 hours and introduced into a glass tank containing 1L of pond water with 200 larvae (4th instar) of Aedes aegypti. Number of larvae survived in the tank was enumerated hourly up to 48 hours. In case where >75% of larvae are consumed by dragonfly nymphs, additional Ae. aegypti larvae were introduced into such tanks. Experiment was repeated for five times. Same procedure was followed with different stages of growth of the dragonfly nymphs characterized by the highest predation rate. General Linear Model followed by Tukey's pairwise comparison was used for statistical analysis. RESULTS: The predation rates of different dragonfly species varied significantly (p<0.05), whereby Anax indicus (110±7.14 per day) indicated the highest, followed by Pantala flavescens (54.07±5.15) and Gynacantha dravida (49.00±11.89), while Tholymis tillarga (23.47±2.48) had the lowest. Further, significant variations in the larval predation were found among different maturity stages (10-20; 25-35; and 35-45 mm in body length) of Ana. indicus (p<0.05). Regardless of statistical significance, a relatively higher larvicidal activity was observed at dusk than in dawn. Conclusion. Ana. indicus, which is characterized by the highest predation rate, and P. flavescens that has the widest geographical distribution within Sri Lanka along with a notable predation efficacy could be recommended as potential candidates for field trials in biological control of dengue outbreaks via suppression of Ae. aegypti larvae.
Larval indices of vector mosquitoes as predictors of dengue epidemics: An approach to manage dengue outbreaks based on entomological parameters in the districts of Colombo and Kandy, Sri Lanka
(Hindawi Pub. Co., 2020) Udayanga, L.; Aryaprema, S.; Gunathilaka, N.; Iqbal, M. C. M.; Fernando, T.; Abeyewickreme, W.
BACKGROUND: Early detection of dengue epidemics is a vital aspect in control programmes. Predictions based on larval indices of disease vectors are widely used in dengue control, with defined threshold values. However, there is no set threshold in Sri Lanka at the national or regional levels for Aedes larval indices. Therefore, the current study aimed at developing threshold values for vector indices in two dengue high-risk districts in Sri Lanka. METHODS: Monthly vector indices (House Index [HI], Container Index [CI], Breteau Index for Aedes aegypti [BIagp], and Ae. albopictus [BIalb]), of ten selected dengue high-risk Medical Officer of Health (MOH) areas located in Colombo and Kandy districts, were collected from January 2010 to June 2019, along with monthly reported dengue cases. Receiver Operating Characteristic (ROC) curve analysis in SPSS (version 23) was used to assess the discriminative power of the larval indices in identifying dengue epidemics and to develop thresholds for the dengue epidemic management. RESULTS: Only HI and BIagp denoted significant associations with dengue epidemics at lag periods of one and two months. Based on Ae. aegypti, average threshold values were defined for Colombo as Low Risk (2.4 ≤ BIagp < 3.8), Moderate Risk (3.8 ≤ BIagp < 5), High Risk (BIagp ≥ 5), along with BIagp 2.9 ≤ BIagp < 4.2 (Low Risk), 4.2 ≤ BIagp < 5.3 (Moderate Risk), and BIagp ≥ 5.3 (High Risk) for Kandy. Further, 5.5 ≤ HI < 8.9, 8.9 ≤ HI < 11.9, and HI ≥ 11.9 were defined as Low Risk, Moderate Risk, and High Risk average thresholds for HI in Colombo, while 6.9 ≤ HI < 9.1 (Low Risk), 8.9 ≥ HI < 11.8 (Moderate Risk), and HI ≥ 11.8 (High Risk) were defined for Kandy. CONCLUSIONS: The defined threshold values for Ae. aegypti and HI could be recommended as indicators for early detection of dengue epidemics and to drive vector management activities, with the objective of managing dengue epidemics with optimal usage of financial, technical, and human resources in Sri Lanka.
Climate change induced vulnerability and adaption for dengue incidence in Colombo and Kandy districts: the detailed investigation in Sri Lanka
(BioMed Central., 2020) Udayanga, L.; Gunathilaka, N.; Iqbal, M. C. M.; Abeyewickreme, W.
BACKGROUND: Assessing the vulnerability of an infectious disease such as dengue among endemic population is an important requirement to design proactive programmes in order to improve resilience capacity of vulnerable communities. The current study aimed to evaluate the climate change induced socio-economic vulnerability of local communities to dengue in Colombo and Kandy districts of Sri Lanka. METHODS: A total of 42 variables (entomological, epidemiological, meteorological parameters, land-use practices and socio-demographic data) of all the 38 Medical Officer of Health (MOH) areas in the districts of Colombo and Kandy were considered as candidate variables for a composite index based vulnerability assessment. The Principal Component Analysis (PCA) was used in selecting and setting the weight for each indicator. Exposure, Sensitivity, Adaptive Capacity and Vulnerability of all MOH areas for dengue were calculated using the composite index approach recommended by the Intergovernmental Panel on Climate Change. RESULTS: Out of 42 candidate variables, only 23 parameters (Exposure Index: six variables; Sensitivity Index: 11 variables; Adaptive Capacity Index: six variables) were selected as indicators to assess climate change vulnerability to dengue. Colombo Municipal Council (CMC) MOH area denoted the highest values for exposure (0.89: exceptionally high exposure), sensitivity (0.86: exceptionally high sensitivity) in Colombo, while Kandy Municipal Council (KMC) area reported the highest exposure (0.79: high exposure) and sensitivity (0.77: high sensitivity) in Kandy. Piliyandala MOH area denoted the highest level of adaptive capacity (0.66) in Colombo followed by Menikhinna (0.68) in Kandy. The highest vulnerability (0.45: moderate vulnerability) to dengue was indicated from CMC and the lowest indicated from Galaha MOH (0.15; very low vulnerability) in Kandy. Interestingly the KMC MOH area had a notable vulnerability of 0.41 (moderate vulnerability), which was the highest within Kandy. CONCLUSIONS: In general, vulnerability for dengue was relatively higher within the MOH areas of Colombo, than in Kandy, suggesting a higher degree of potential susceptibility to dengue within and among local communities of Colombo. Vector Controlling Entities are recommended to consider the spatial variations in vulnerability of local communities to dengue for decision making, especially in allocation of limited financial, human and mechanical resources for dengue epidemic management. KEYWORDS: Climate change; Dengue; Sri Lanka; Vulnerability.
Prevalence of cutaneous leishmaniasis infection and clinico-epidemiological patterns among military personnel in Mullaitivu and Kilinochchi districts of the Northern Province, early war-torn areas in Sri Lanka.
(BioMed Central, 2020) Gunathilaka, N.; Semege, S.; Pathirana, N.; Manamperi, N.; Udayanga, L.; Wijesinghe, H.; Premaratne, P.; Fernando, D.
BACKGROUND: The 30-year-old armed conflict in Sri Lanka resulted in a general breakdown of civil administration in the Northern and Eastern provinces, leading to mobilisation of many armed forces personnel to assist with reconstruction and resettlement. This occupational group has been identified as a priority risk group for leishmaniasis. METHODS: Individuals enlisted at all military establishments in Mullaitivu and Kilinochchi districts, Northern Province of Sri Lanka were included. Five thousand individuals were screened for skin lesions between September 2018 and August 2019. Persons with lesions suspected as cutaneous leishmaniasis (CL) were further investigated. Information on sociodemographic/other potential risk factors was obtained through an interviewer-administered structured questionnaire. The diagnosis was confirmed by microscopic visualization of parasitic stages from different samples obtained (skin scraping, lesion aspirate and tissue impression smears), histopathology and polymerase chain reaction DNA amplification. RESULTS: Among 5000 individuals screened, 74 individuals were suspected of having CL. Of these, 67.6% (n = 50) patients were confirmed for CL by microscopy. Around two third of both males (67.6%; n = 48) and females (66.6%; n = 2) were positive for Leishmania. The soldiers belonging to 26-35-year age group reported the highest susceptibility (83.3%; OR: 4.83, 95% CI: 3.49-6.20%). Of the sociodemographic factors, age, wearing short-sleeved upper body clothing as the uniform and non-use of insect repellents were identified as significant risk factors. Most of the CL patients had a single lesion (86.0%; n = 43) of an ulcerative type (34.0%; n = 17), mostly on their upper limb (67.9%; n = 34). Lesions were mostly 5-10 mm diameter (59.9%; n = 30) in size with poorly defined margins (72.0%; n = 36). Amongst the diagnostic techniques, microscopic examination of slit skin smear and tissue impression smear were able to discriminate the majority of patients (92.1%; n = 46) for CL. CONCLUSIONS: In order to highlight the true burden of leishmaniasis in the military personnel, cases of leishmaniasis from military institutes should be recognized as a different entity per say and be included in the national figures so as to depict the real magnitude of the disease burden amongst this high-risk group. KEYWORDS: Clinical; Cutaneous leishmaniasis; Epidemiological; War-torn areas.
Field-based evaluation of Novaluron EC10 insect growth regulator, a chitin synthesis inhibitor against Dengue vector breeding in leaf axils of pineapple plantations in Gampaha district, Sri Lanka
(BioMed Central, 2020) Gunathilaka, N.; Ranathunga, T.; Hettiarachchi, D.; Udayanga, L.; Abeyewickreme, W.
BACKGROUND: Insect growth regulators (IGRs) are considered a novel group of insecticides to control mosquitoes. Novaluron is an IGR with benzoylphenyl urea insecticide, which inhibits chitin synthesis in insects and can reduce insect population density; it is also known to have a high margin of safety for mammals. METHODS: The effective minimum concentration of novaluron formulation EC10 was tested. Six pineapple plantations [control (n = 3) and test (n = 3)] were selected from Meerigama Medical Officer of Health area in Gampaha District, Sri Lanka. Fifteen plots (10 × 10 m) were demarcated in each site with a 200 m distance apart. Leaf axils of 450 pineapple plants (30 plants × 15 plots) were screened for immature stages of Aedes mosquitoes weekly for 12 weeks. The required concentration (20 ppm) of novaluron was sprayed onto the selected pineapple plants (n = 1350) individually in 3 selected test sites for 5-10 s. The reduction in the vector population was interpreted as the percentage of reduction in immature stages of Aedes mosquitoes. RESULTS: The 100% mortality of the Ae. aegypti larvae within 24 h was observed at 20 ppm (0.05 ml of novaluron 100 g/l in 250 ml of water) as the minimum dose. Variation in the number of Aedes larvae present in the control and intervention sites was found to be significantly different throughout the entire observational period (χ2 = 128.29, df = 11, P < 0.001). The total elimination of Aedes larvae continued for up to 2 weeks and a 50% reduction was observed until the 8th week. CONCLUSIONS: The present study emphasizes that novaluron (10% EC) can be used as an effective larvicide at the treatment dose of 20 ppm. The residual effect of the IGR lasted for 12 weeks with a functional efficacy of 8 weeks. The 100% reduction of larval breeding was observed up to the 2nd week after application and the percentage reduction of immature stages remained > 50% until the 8th week. The lowest reduction (34.2%) was observed at 12 weeks after the initial treatment. Therefore, re-treatment may be recommended based on the reduction in the efficacy of the IGR. Keywords: Aedes; Field efficacy; Insect growth regulator; Novaluron; Pineapple plantation.

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