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This repository contains the published and unpublished research of the Faculty of Medicine by the staff members of the faculty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 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 Characterization of the sibling species status of Anopheles culicifacies breeding in polluted water bodies in Trincomalee District of Sri Lanka(Sri Lanka Association for the Advancement of Science, 2015) Gunathilaka, P.A.D.H.N.; Prashath, K.; Abeyewickreme, W.Anopheles culicifacies, the major vector of malaria in Sri Lanka, is known to breed in clean and clear water. However, recent findings have confirmed breeding in waste water containing drains. However, no study has been conducted to identify whether it is vector or non vector siblings. Therefore, the objective of the study was to identify the sibling species status of An. culicifacies breeding in waste water containing drains. An. culicifacies adult samples (Reared from larvae) were obtained from the Padavisiripura Entomological team attached to Tropical and Environmental Diseases and Health Associates (TEDHA) Malaria Elimination Program in the Trincomalee District. The collected mosquito specimens were processed for the extraction of genomic DNA individually. The PCR amplifications were carried out using different primer combinations for differentiating species A from D, species B from C, species B from E, and species B, C, and E from each other. The results obtained from the gel electrophoresis were compared with the marker, and band sizes of 359 bp, 248 bp, 95 + 248 bp, 166 + 359 bp and 178 + 248 bp were used to identify the sibling species A, B, C, D and E respectively. The molecular biological identification of the field caught An. culicifacies samples indicated that only 6.25% (1/16) represented sibling species B. About 93.75% (15/16) of the samples were An. culicifacies sibling species E. According to the results, the majority of the species belongs to sibling species E which is considered as the vector sibling species of An. culicifacies. This is the first time that An. culicifcicies E breeding in waste water was confirmed by a molecular method. However, malaria control programs focus on rural communities as a result of bio-ecology of Anopheles mosquitoes. Therefore, unusual breeding habitats such as waste water collections may mislead the current vector controlling programs. These results reconfirm that An. culicifacies has adapted to breed in water bodies including waste water collections. Since a majority of them belong to sibling E, which is considered as the vector, this may adversely affect the current malaria elimination program. Therefore, new strategies should be adopted to control malaria vector breeding in these unusual breeding habitats under the current malaria elimination program in Sri Lanka.Item Breeding habitat diversity and species composition of Anopheles mosquitoes in Trincomalee district, Sri Lanaka(HABITATS Conservation Initiative, 2014) Gunathilaka, P.A.D.H.N.; Fernando, M.A.S.T.; Hapugoda, M.D.; Wijeyerathne, P.; Wickremasinghe, A.R.; Abeyewickreme, W.Entomological studies on the abundance of malaria vector Anopheles mosquitoes have not been studied in some malaria endemic areas of Sri Lanka over past 30 years in view of the security situation. The aim of this study was to explore the habitat diversity and distribution of anopheline species in Trincomalee District in order to prioritize vector breeding habitats for developing timely and cost effective larval controlling measures. Potential larval habitats for Anopheles mosquitoes were surveyed from June 2010 - December 2010, in selected sampling sites in the Trincomalee District; Gomarankadawala, Echchallampaththu, Mollipothana, Thoppur and Padavisiripura, within a radius about 20 km on weekly basis. The species distribution and density were calculated. A total of 3,701 larval specimens representing twelve Anopheles species were reported form 19 breeding habitats (Tank margin, main canal, paddy field, vegetative canal, lake, built well, burrow pit, distribution canal, pond, rock pool, canal, un-built well, common well, river margin, sand pool, animal foot print, rain water collection, quarry pit and marshy land). Ten habitats were categorized under structurally complex group based on the presence of biotic communities. Only An. subpictus can be regarded as constant according to Distribution (C) (C= 80.1-100%).An. nigerrimus, An. peditaeniatus, An. pallidus and An. vagus were frequent (C= 60.1 – 80%). An. varuna, An. barbirostris, An. annularis and An. barbumbrosus were shown as infrequent species (C= 20.1 – 40%) and other namely An. aconitus, An. culicifacies and An. jamesii can be categorized under sporadic appearance (C= 0 – 20%). According to Density (D) criterion, five species (An. subpictus, An. nigerrimus, An. varuna, An. pallidus, An. barbumbrosus) were within the dominant class (D > 5%). Four species (An. vagus, An. peditaeniatus, An. annularis, An. aconitus) were in the subdominant class (1< D <5%). Only An. jamesii and An. culicifacies were the satellite species (D < 1%).Item Breeding of Anopheles culicifacies in different waterbodies in the district of Trincomalee(University of Kelaniya, 2012) Gunathilaka, P.A.D.H.N.; Fernando, M.A.S.T.; Hapugoda, M.D.; Wijeyerathne, P.; Wickremasinghe, A.R.; Abeyewickreme, W.Introduction: Anopheles culicifacies (Diptera: Culicidae), the major vector of malaria in Sri Lanka is known to breed in clean and clear water. This study was focused to understand the larval habitats of the major malaria vector with the eco system changes in the Trincomalee district of the Eastern Province. Method: Potential larval habitats for Anopheles mosquitoes were surveyed on a monthly basis for 17 months (January 2011 –June 2012) in 4 different selected sampling sites (Murthankulam, Kommnaimottai, Paranamadawachchiya and Kokmotawewa). Collected larvae were identified using standard taxonomic keys. The species Distribution (C) and Density (D) were calculated. Results: A total of 2996 larval specimens representing 13 Anopheles species were reported from 16 different breeding habitats namely, waste water (n= 635), built well (n= 1229), earth well (n=149), agricultural well (n=9), rain water collection (n=89), animal hoof print (n=17), burrow pit (n=256), rock pool (n=10), canal (n=15), irrigation canal (n=27), lake margin (n=27), tank margin (n=448), pond margin (n=15), marshy land (n=13), paddy field (n=15) and slow moving water (n=42). An. culicifacies was observed as the most predominant species throughout the survey. According to Density criterion, An. culicifacies (44.0%), An. subpictus (19.2%), An. barbirostris (13.2%), An. peditaeniatus (10.28%) and An. nigerrimus (8.7%) were within the dominant class; (D > 5%). Two species (An. vagus, An. pallidus) were in the subdominant class (1< D <5%). Only An. annularis, An. varuna, An. barbumbrosus, An. pseudojamesi, An. jamesii and An. tessellatus were the satellite species (D < 1%). An. nigerrimus, An. subpictus and An. peditaeniatus can be regarded as constant according to distribution (C= 80.1-100%). Only An. vagus was the most frequently reported (C= 60.1 – 80%) species. All other Anopheles including An. culicifacies were observed as infrequent species (C= 20.1 – 40%) and no species was identified as sporadic appearance (C= 0 – 20%). Most productive breeding site for An. culicifacies were drains covered with waste water (Density= 81.57%) in remote areas. Interpretation & conclusion: These results indicate that An. culicifacies has adapted to breed in a wide range of water bodies including waste water collections although they are considered to breed in clean and clear water. The survival of the major vector mosquito in widespread water bodies could be responsible for the increase in the incidence of malaria in the future.Item Blood-feeding patterns of Anopheles mosquitoes in malaria-endemic areas of Sri Lanka(University of Kelaniya, 2012) Gunathilaka, P.A.D.H.N.; Fernando, M.A.S.T.; Hapugoda, M.D.; Wijeyerathne, P.; Wickremasinghe, A.R.; Abeyewickreme, W.Background: Studies on host preference patterns in blood-feeding of anopheline mosquitoes are crucial for incriminating them as malaria vectors. However, little information is available on the host preferences of Anopheles mosquitoes in Sri Lanka. Therefore, the objective of the present study was to determine the hematophagic tendency of the anophelines. Methods: Adult Anopheles mosquitoes were collected using Cattle Baited Trap Collection (CBTC), Cattle Baited Net Collection (CBNC), Window Trap Collection (WTC), and Hand Collection (HC) from selected sentinel sites in Mannnar (3) and Trincomalee (5) Districts during June 2011- June 2012. Each blood fed mosquito was processed in to 9 cm whatman filter papers within 24 hours after blood meal has taken. DNA was extracted using the dried blood meal protocol of the QIAmp DNA mini kit. A multiplexed, Real Time Polymerase Reaction (RT- PCR) assay targeting 8 animals was developed for two panels (Panel 1: Bovine, cat, pig, monkey: Panel 2: Human, rat, dog, chicken) to identify the host meal of Anopheles. Human Blood Index (HBI), Forage Ratio (FR) and Host Feeding Index (HFI) were calculated. Results: A total of 216 field caught freshly engorged females mosquitoes belonging to 12 Anopheles species was analyzed. The host preference of anophelines observed in this study was bovine (86.17%), human (1.84%), cat (0.46%) and pig (0.46%). Only 6.91 % was positive for both human and bovine. In addition 5.0 % of the total samples tested were unknown. The overall HBI and HFI in the present study were low indicating the humans were not the preferred host for the tested anopheline species. Nevertheless, a small proportion engorged An. aconitus (0.37), An. culicifacies (0.27), An. barbirostris (0.2), An. annularis (0.125) and An. subpictus (0.12), An. peditaeniatus (0.08), An. pseudojamesi (0.04) and An. barbumbrosus (0.04) contained human blood, The FRs for human were <1.0 for most of the anophelines, except An. aconitus (1.04). Conclusion: The presence of human blood, in mosquito species indicates the possibility of them transmitting malaria. Hence, further studies on vector competence are needed to determine the role of each of the above anopheline species currently as efficient vectors of malaria.Item 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.Item Morphological differences among Anopheles subpictus sibling species B breeding in waste water habitats in Mannar District, Sri Lanka(University of Kelaniya, 2011) Gunathilaka, P.A.D.H.N.; Fernando, M.A.S.T.; Premasiri, D.S.; Hapugoda, M.D.; Wijeyerathne, P.; Wickremasinghe, A.R.; Abeyewickreme, W.Anopheles culicifacies and An. subpictus are considered as the principal and subsidiary vector for malaria in Sri Lanka respectively. An. subpictus sibling species B has been specifically implicated in transmitting malaria in the coastal areas in the west coast of Sri Lanka. The main objective of this study was to identify morphological similarities and differences of An. subpictus B, breeding in waste water habitats in Mannar District. Waste water breeding habitats in three sampling sites having a radius of 20 km in Mannar District were studied for one year (June 2010 to July 2011). These sampling sites were Mannar town, Vankalai and Silawathura. Anopheles larvae and water samples were collected from each breeding site. Larvae were reared until the adults emerged and identified to the species level by taxonomic keys. Densities of Anopheles larvae were calculated. Adult An. subpictus were prepared for egg laying. Sibling status was basically determined based on the number of ridges in the floats of egg with reference to the available keys. Further, other morphological characters were also examined. Water samples were checked for fourteen abiotic variables (pH, dissolved oxygen, conductivity, hardness, free Ammonia, total dissolved solids, colour, odour, suspended solids, alkalinity, conductivity, chloride, total iron and salinity). Breeding of Anopheles species in waste water habitats was observed only in Silawathura and Vankalai sampling sites. A considerable number of Anopheles larvae were collected (n=1197): An. subpictus (96.6%), An. nigerrimus (2.25%), An. barbirostris (0.67%) and An. pallidus (0.5%). According to standards available for surface waters, qualities of water in selected habitats were in the ranges of third class quality. Egg character based on similarities in number of ridges in the egg, all An. subpictus belong to sibling species B. Although they belong to the same sibling species, they showed some morphological differences in their proboscis and palps. Some mosquitoes showed stunted lebellum in the proboscis and their palps had extended more than the length of proboscis (n= 632). Other members had extended lebellum in their proboscis compared to the length of pals (n=357). With ecological changes mosquito sibling species may shift their breeding habitats in order to reduce competition and to attain a wide dissemination in the environment. It is difficult to determine sibling species status using morphological characters. The existing morphological variations and their use for identifying closely related anopheline mosquitoes, especially when they exist as species complexes, are imprecise and need to be replaced with DNA sequence-based techniques.Item 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.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.