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This repository contains the published and unpublished research of the Faculty of Medicine by the staff members of the faculty

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Author: search.filters.author.de Silva, B.G.D.N.K.

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    Mitochondrial metabolic genes provide phylogeographic relationships of global collections of Aedes aegypti (Diptera: Culicidae)
    (Public Library of Science, 2020) Fernando, H.S.D.; Hapugoda, M.; Perera, R.; Black Iv, W.C.; de Silva, B.G.D.N.K.
    ABSTRACT: Phylogeographic relationships among global collections of the mosquito Aedes aegypti were evaluated using the mitochondrial Cytochrome C Oxidase 1 (CO1) and NADH dehydrogenase subunit 4 (ND4) genes including new sequences from Sri Lanka. Phylogeographic analysis estimated that Ae. aegypti arose as a species ~614 thousand years ago (kya) in the late Pleistocene. At 545 kya an "early" East African clade arose that continued to differentiate in East Africa, and eventually gave rise to three lineages one of which is distributed throughout all tropical and subtropical regions, a second that contains Southeast Asian/Sri Lankan mosquitoes and a third that contains mostly New World mosquitoes. West African collections were not represented in this early clade. The late clade continued to differentiate throughout Africa and gave rise to a lineage that spread globally. The most recent branches of the late clade are represented by South-East Asia and India/Pakistan collections. Analysis of migration rates suggests abundant gene flow between India/Pakistan and the rest of the world with the exception of Africa.
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    Gene flow patterns among Aedes aegypti (Diptera: Culicidae) populations in Sri Lanka
    (MDPI AG, 2020) Fernando, H.S.D.; Hapugoda, M.; Perera, R.; Black Iv, W.C.; de Silva, B.G.D.N.K.
    ABSTRACT:In Sri Lanka, dengue is the most serious arboviral disease. Recent increases in dengue cases suggest a higher infection rate and spread of the disease to new areas. The present study explores gene flow patterns of Ae. aegypti, the main vector of dengue disease, among 10 collection sites including major ports and inland cities using variations at 11 microsatellite loci. Discriminant analysis of principal components (DAPC) and k-means clustering estimated eight genetic clusters. Analysis of Molecular Variance (AMOVA) estimated equal variances among cities and among collections in Colombo, Sri Lanka. Significant evidence, although weak, was detected for isolation by distance. Analysis of gene flow rates and directions using MIGRATE-n indicated that populations throughout the island served as a source of immigrants for Colombo with abundant gene flow among major commercial cities in Sri Lanka, which appear to receive migrant mosquitoes from throughout Sri Lanka. The observed patterns probably arise through human movement of Ae. aegypti during commerce from throughout Sri Lanka into Colombo increasing the risk of spread. The patterns uncovered in this study are significant for global health as Sri Lanka is situated along a key international shipping route. KEYWORDS: Aedes aegypti; Sri Lanka; gene flow patterns; population structure.
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    A Preliminary study of genetic estimates of population structure of Aedes aegypti populations in three districts, Sri Lanka
    (Sri Lanka Association for the Advancement of Science, 2014) Fernando, H.S.D; Hapugoda, M.D.; de Silva, B.G.D.N.K.
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    Prevalence of Anopheline species in Ampara district, Sri Lanka
    (University of Kelaniya, 2012) Fernando, M.A.S.T.; Gunathilaka, P.A.D.H.N.; Hapugoda, M.D.; de Silva, B.G.D.N.K.; Wijeyerathne, P.; Abeyewickreme, W.
    Introduction: Investigating the presence of primary and secondary vectors of malaria in the selected areas where no entomological surveillance was carried out for about 30 years due to ethnic conflict. Objective: To study prevalence of malaria vector in Ampara District and to assess the risk of malaria in the area. Method: Surveillance was preformed from January 2011 to June 2012 in 4 selected areas (i.e. Panama, Thirukkovil, Mahaoya and Dehiattakandiya) in Ampara District. From each area 4 localities (total 16 localities) were selected for the sample collection in order to ensure full coverage of the District. Cattle Baited Hut Collection (CBHC) and Cattle Baited Net Collection (CBNC) were performed as sample collecting methods on monthly basis throughout the surveillance period. Results: Mosquito densities for each collected Anopheles species were calculated as density per hut or net for CBHT and CBNT respectively. 14 Anopheles species were recorded from CBHC with high prevalence for An. subpictus (68.58%), An. nigerrimus (14.02%) and An. vagus (6.73%). 16 Anopheles species were recorded from CBNC with high prevelance of An. nigerrimus (50.07%), An. peditaeniatus (16.12%), An. pseudojemesi (9.21%) and An. subpictus (7.68%). An. culicifacies (primary malaria vector in Sri Lanka) recorded with lesser densities but An. subpictus, the secondary vector for malaria in Sri Lanka was predominant thorough out this study. Conclusions: The presence of primary and secondary malaria vectors in the area may cause a malaria epidemic in these areas. Hence, it is essential to study the seasonal prevalence of Anopheles species in order to initiate timely controlling measures in Ampara District.
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    Study on house dwelling Anopheline species in Batticaloa District, Sri Lanka
    (University of Kelaniya, 2011) Fernando, M.A.S.T.; Gunathilaka, P.A.D.H.N.; Hapugoda, M.D.; Abeyewickreme, W.; de Silva, B.G.D.N.K.; Wijeyerathne, P.
    Even though the malaria cases are less, vectors which transmit the disease are still present. No proper vector surveys have been carried out in the eastern area of Sri Lanka for more than 30 years, due to the ethnic conflict. The objective is to study house dwelling Anopheline densities to assess the risk of malaria prior to eliminating malaria, and implementing vector control strategies. Surveillance was preformed from July 2010 to December 2010 in 3 selected areas (i.e. Mandur, Vakanery, and Vakarai) in Batticaloa District. Each area was divided into 4 sub sampling sites attaining a total of 12 sub sites in order to ensure full coverage of the whole district. Hand Catch and Window Trap collections were continued to collect mosquito specimens from 44 randomly selected houses in each sub site (n= 528) on a weekly basis. Mosquito densities for each collected Anopheles species were calculated as density per man hour and density per trap for both Hand Catch and Window Trap Collection respectively. Four species were recorded from Hand Catch (i.e. An. barbirostris (0.002), An. nigerrimus (0.081), An. subpictus (1.813) and An. vagus (0.005)). Four species observed from Window Trap Collection (i.e. An. nigerrimus (0.067), An. subpictus (0.700), An. vagus (0.010) and An. varuna (0.174)). An. subpictus, the secondary vector for Malaria in Sri Lanka was predominant throughout this study. The presence of some Anopheline mosquitoes which can act as potential malaria vectors may cause malaria epidemics in these areas. Hence, it is essential to continue more surveillance related to Larval and Trap collections to get the entire picture of Vector composition and prevalence in Batticaloa District.
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    A Simplified non radioactive DNA probe technique for the field detection of sibling species A of the Anopheles culicifacies (Diptera: Culicidae) complex
    (University of Sri Jayewardenepura, 2010) de Silva, B.G.D.N.K.; Hapugoda, G.P.G.M.D.; Karunanayake, E.H.
    Three cloned highly repetitive DNA sequences Rp36, Rp217 and Rp234 isolated from An. culicifacies Giles, sensu lato were developed as non radioactive DNA probes by using a biotinylated labeling and colorimetric detection system. These non radioactive DNA probes distinguish sibling species A from species B and C of the An. culicifacies complex in a dot blot hybridization assay using single mosquito DNA extracts diluted 50 fold. The biotinylated Rp217 probe was further assayed in a more simple procedure which involves the hybridization of blots prepared from squashed mosquito heads. This technique avoids the separate extraction of mosquito DNA and facilitates a number of samples to be processed rapidly while also allowing several field analyses to be carried out on one mosquito specimen.
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    ITS-2 secondary structures and phylogeny of Anopheles culicifacies species
    (Biomedical Informatics Pub. Group, 2008) Dassanayake, R.S.; Gunawardene, Y.I.N.S.; de Silva, B.G.D.N.K.
    BACKGROUND: Second internal transcribed spacer (ITS2) has proven to contain useful biological information at higher taxonomic levels. OBJECTIVES: This study was carried out to unravel the biological information in the ITS2 region of An. culicifacies and the internal relationships between the five species of Anopheles culicifacies.METHODOLOGY: In achieving these objectives, twenty two ITS2 sequences (approximately 370bp) of An. culicifacies species were retrieved from GenBank and secondary structures were generated. For the refinement of the primary structures, i.e. nucleotide sequence of ITS2 sequences, generated secondary structures were used. The improved ITS2 primary structures sequences were then aligned and used for the construction of phylogenetic trees. RESULTS AND DISCUSSIONS: ITS2 secondary structures of culicifacies closely resembled near universal eukaryotes secondary structure and had three helices, and the structures of helix II and distal region of helix III of ITS2 of An. culicifacies were strikingly similar to those regions of other organisms strengthening possible involvement of these regions in rRNA biogenesis. Phylogenetic analysis of improved ITS2 sequences revealed two main clades one representing sibling B, C and E and A and D in the other. CONCLUSIONS: Near sequence identity of ITS2 regions of the members in a particular clade indicate that this region is undergoing parallel evolution to perform clade specific RNA biogenesis. The divergence of certain isolates of An. culicifacies from main clades in phylogenetic analyses suggests the possible existence of camouflaged sub-species within the complex of culicifacies. Using the fixed nucleotide differences, we estimate that these two clades have diverged nearly 3.3 million years ago, while the sibling species in clade 2 are under less evolutionary pressure, which may have evolved much later than the members in clade 1.
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    Seasonal Trends of Anopheles Culicifacies population at Gomadiyagala, a village in a North Western Province of Sri Lanka
    (University of Sri Jayewardenepura, 1998) de Silva, B.G.D.N.K.; Gunasekera, M.B.; Abeyewickreme, W.; Wickremasinghe, M.B.
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    Screening of Anopheles crlicifacies population of Sri Lanka for sibling species A.
    (Thacker's Press and Directories for Indian Research Fund Association, 1998) de Silva, B.G.D.N.K.; Gunasekera, M.B.; Abeyewickreme, W.; Abhayawardena, T.A.; Karunanayake, E.H.
    A total of 1119 Anopheles culicifacies mosquitoes collected from various malaria endemic regions in Sri Lanka were examined using two DNA probes Rp217 and Rp234, which enable the differentiation of sibling species A from B and C species of An. culicifacies. Sibling species A was found to be absent.
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    Development of DNA probes for the identification of sibling species A of the Anopheles culicifacies(Diptera Culicidae) Complex
    (CABI Publishing, 1995) Gunasekera, M.B.; de Silva, B.G.D.N.K.; Abeyewickreme, W.; Subbarao, S.K.; Nandadasa, H.G.; Karunanayake, E.H.
    Three highly repetitive DNA sequences, Rp36, Rp217 and Rp234, were isolated from A. culicifacies s.l. The cloned DNA sequences were found at a higher copy number in species B and C, than in species A of the A. culicifacies complex. These sequences may therefore be used as DNA probes to distinguish species A from the other 2 species, using a 200-fold dilution of a single mosquito DNA extract in a dot-blot hybridization assay. Rp36 and Rp217 were completely sequenced. Internal repeats were absent in Rp36. Two related core sequences of 134 and 16 bp were found tandemly repeated in Rp217. These probes enable the rapid detection of species A of A. culicifacies in field investigations
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