Journal/Magazine Articles
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This collection contains original research articles, review articles and case reports published in local and international peer reviewed journals by the staff members of the Faculty of Medicine
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Item Occurrence of major and potential malaria vector immature stages in different breeding habitats and associated biotic and abiotic characters in the district of Trincomalee Sri Lanka(New Delhi : National Institute of Malaria Research, 2020) Ranathunge, R.M.T.B.; Kannangara, D.N.; Gunathilaka, P.A.D.H.N.; Abeyewickreme, W.; Hapugoda, M.D.BACKGROUND & OBJECTIVES: Understanding the effect of biotic and abiotic factors on the biology and ecology of immature stages of anopheline larvae is very important in controlling malaria vector mosquitoes. Therefore, this study was focused on the monitoring of ecological factors affecting the distribution, dynamics, and density of malaria vector mosquitoes in the District of Trincomalee, Sri Lanka. METHODS: Permanent and temporary breeding habitats were identified and selected from five possible malaria sensitive sites in the district of Trincomalee. Anopheles larvae and macro-invertebrates were collected using standard methods for 16 months (from October 2013 to January 2015) and they were identified microscopically. Eight physico-chemical parameters of the breeding habitats were measured. RESULTS: Overall, a total of 4815 anopheline larvae belonging to 13 species were collected from 3,12,764 dips from 18 permanent and temporary breeding habitats. The abundance of anopheline larvae showed a significant positive correlation (p <0.05) with physico-chemical parameters in breeding habitats, such as temperature, dissolved oxygen, and turbidity. A total of 35 macro-invertebrate taxa were collected from the anopheline mosquito breeding habitats. INTERPRETATION & CONCLUSION: This study represents the first systematic update of water quality parameters, macro-invertebrate communities associated with Anopheles mosquito oviposition sites in the District of Trincomalee, Sri Lanka. Rainfall intensity and wind speed are critical meteorological factors for the distribution and abundance of malaria vectors. Knowledge generated on the ecology of Anopheles mosquitoes will help to eliminate malaria vectors in the country. KEYWORDS: Macro-invertebrates; Sri Lanka; malaria vectors; physico-chemical parameters.Item Multivariate spatio-temporal approach to identify vulnerable localities in dengue risk areas using Geographic Information System (GIS)(Nature Publishing Group, 2021) Withanage, G.P.; Gunawardana, M.; Viswakula, S.D.; Samaraweera, K.; Gunawardene, N.S.; Hapugoda, M.D.ABSTRACT: Dengue is one of the most important vector-borne infection in Sri Lanka currently leading to vast economic and social burden. Neither a vaccine nor drug is still not being practiced, vector controlling is the best approach to control disease transmission in the country. Therefore, early warning systems are imminent requirement. The aim of the study was to develop Geographic Information System (GIS)-based multivariate analysis model to detect risk hotspots of dengue in the Gampaha District, Sri Lanka to control diseases transmission. A risk model and spatial Poisson point process model were developed using separate layers for patient incidence locations, positive breeding containers, roads, total buildings, public places, land use maps and elevation in four high risk areas in the district. Spatial correlations of each study layer with patient incidences was identified using Kernel density and Euclidean distance functions with minimum allowed distance parameter. Output files of risk model indicate that high risk localities are in close proximity to roads and coincide with vegetation coverage while the Poisson model highlighted the proximity of high intensity localities to public places and possibility of artificial reservoirs of dengue. The latter model further indicate that clustering of dengue cases in a radius of approximately 150 m in high risk areas indicating areas need intensive attention in future vector surveillances.Item Use of novaluron-based autocidal gravid ovitraps to control Aedes dengue vector mosquitoes in the district of Gampaha, Sri Lanka(Hindawi Pub. Co., 2020) Withanage, G.P.; Viswakula, S.D.; Gunawardene, Y.I.N.S.; Hapugoda, M.D.ABSTRACT:Dengue is the most important mosquito-borne viral infection in Sri Lanka causing an enormous social and economic burden in the country. In the absence of therapeutic drugs and the developed vaccines are under investigation, vector control is the best strategy to reduce the disease transmission. Therefore, the development of novel tools to control dengue vector mosquitoes has become the need of the hour. Novaluron is a recently developed Insect Growth Regulator (IGR) which inhibits chitin synthesis in immature stages of insects. The aim of the study was to identify the efficacy of a simple and cost-effective Autocidal Gravid Ovitrap (AGO) developed using Novaluron to control dengue outbreaks in the District of Gampaha, Sri Lanka. Laboratory and semifield experiments were performed to identify the activity range, optimum field dosage, and residual effects of Novaluron following the World Health Organization guidelines, and field experiments were performed in the Ragama Medical Officer of Health (MOH) area. Two study areas 800 m apart were selected and assigned as treated and control areas randomly. In each study area, 30 households were selected randomly. Each household was given two ovitraps, one placed indoors and the other placed outdoors. Mortality and survival counts were recorded separately for one-year time period and data were analyzed using a two-way repeated measures analysis of variance model. During the laboratory experiments, the adult emerging inhibition was 100% in all tested concentrations. The optimum field dosage was 2 ppm and the residual effect was 28 days. In the field experiments, significantly higher mortality counts were recorded in treated areas both indoor- and outdoor-placed AGOs. Two-factor repeated measures ANOVA followed by Tukey's test confirmed that the mean mortality count is high for the developed AGOs both indoor and outdoor settings. The developed AGO can be deployed to control both indoor and outdoor dengue vector mosquito populations, and in dengue-risk areas, the ovitrap will be supportive to local health authorities to enhance the efficiency of future vector control programs.Item A forecasting model for dengue incidence in the District of Gampaha, Sri Lanka(BioMed Central, 2018) Withanage, G.P.; Viswakula, S.D.; Nilmini Silva Gunawardena, Y.I.; Hapugoda, M.D.BACKGROUND: Dengue is one of the major health problems in Sri Lanka causing an enormous social and economic burden to the country. An accurate early warning system can enhance the efficiency of preventive measures. The aim of the study was to develop and validate a simple accurate forecasting model for the District of Gampaha, Sri Lanka. Three time-series regression models were developed using monthly rainfall, rainy days, temperature, humidity, wind speed and retrospective dengue incidences over the period January 2012 to November 2015 for the District of Gampaha, Sri Lanka. Various lag times were analyzed to identify optimum forecasting periods including interactions of multiple lags. The models were validated using epidemiological data from December 2015 to November 2017. Prepared models were compared based on Akaike's information criterion, Bayesian information criterion and residual analysis. RESULTS: The selected model forecasted correctly with mean absolute errors of 0.07 and 0.22, and root mean squared errors of 0.09 and 0.28, for training and validation periods, respectively. There were no dengue epidemics observed in the district during the training period and nine outbreaks occurred during the forecasting period. The proposed model captured five outbreaks and correctly rejected 14 within the testing period of 24 months. The Pierce skill score of the model was 0.49, with a receiver operating characteristic of 86% and 92% sensitivity. CONCLUSIONS: The developed weather based forecasting model allows warnings of impending dengue outbreaks and epidemics in advance of one month with high accuracy. Depending upon climatic factors, the previous month's dengue cases had a significant effect on the dengue incidences of the current month. The simple, precise and understandable forecasting model developed could be used to manage limited public health resources effectively for patient management, vector surveillance and intervention programmes in the district.Item Identification of cattle, buffaloes and rodents as reservoir animals of Leptospira in the District of Gampaha, Sri Lanka(Biomed Central, 2017) Denipitiya, D.T.H.; Chandrasekharan, N.V.; Abeyewickreme, W.; Hartskeerl, R.A.; Hapugoda, M.D.BACKGROUND: Leptospirosis is an important emerging infectious disease in Sri Lanka. Rats are the most important reservoir of Leptospira but domestic and wild mammals may also act as important maintenance or accidental hosts. In Sri Lanka, knowledge of reservoir animals of leptospires is poor. The objective of this study was to identify potential reservoir animals of Leptospira in the District of Gampaha, Sri Lanka. FINDINGS: Blood and kidney samples were collected from 38 rodents and mid-stream urine samples were randomly collected from 45 cattle and five buffaloes in the District of Gampaha. Kidney and urine samples were tested by real-time polymerase chain reaction (PCR) and serum samples were tested by the microscopic agglutination test (MAT). Of the 38 rodent kidney samples, 11% (4/38) were positive by real-time PCR. The prevalence of leptospiral carriage was 11% (3/26) and 8% (1/12) in female and male rodents, respectively. Three rodent serum samples were positive by MAT. Of the 50 cattle/buffalo urine samples tested, 10% (5/50) were positive by real-time PCR. The prevalence of leptospiral carriage was 9% (4/45) and 20% (1/5) in cattle and buffaloes, respectively. CONCLUSION: Results of PCR and MAT showed that Leptospira were present in a significant proportion of the rodents and farm animals tested in this study and suggest that these (semi-) domestic animals form an infection reservoir for Leptospira. Therefore, there is a potential zoonotic risk to public health, most notably to farmers in this area.Item Composition of malaria vectors and diversity of anopheline breeding habitats in the district of Mannar, Sri Lanka(Central Environmental Authority (CEA), 2016) Gunathilaka, P.A.D.H.N.; Hapugoda, M.D.; Wickremasinghe, A.R.; Abeyewickreme, W.In the malaria elimination phase in Sri Lanka, investigation on biological and ecological factors of malaria vectors are important in planning appropriate vector controlling strategies. Lack of sufficient biological and ecological information on malaria vectors in the Northern Province of the country, a malaria endemic region, is a major constrain in successful implementation of malaria control programmes. Therefore, the objective of this study was to explore the diversity of breeding habitats and species composition of malaria vector mosquitoes in the District of Mannar, Sri Lanka. Potential habitats for Anopheles mosquito larvae were surveyed from June, 2010 to July 20 J2 on a monthly basis in selected sampling sites in the Mannar District: Mannar Town, Vankalai and Silawathiura, within a radius about 20 km. In each site, 4 sub sites were selected A total of 37,788 Anopheles representing ten species was recorded from 12 breeding habitat categories. Built wells and waste water collections were conducive for anopheline breeding. Anopheles subpictus (96.2%, n= 36,351) was the dominant species followed by An. peditaeniatus (1.47%, n= 557), An. barbirostris (1.23%, n= 463), An. nigerriums (0.75%,n = 285), An. varuna (0.19%, n= 74), An. barbumbrosus (0.1%, n= 38), An. vagus' (0.03%, n= 12), An. pallidus (0.01%, n= 4), An.jamesii (0.05%, n= 2) and An. pseudojamesi (0.05%, n= 2). Use of wells and waste water drains as breeding places by potential malaria vectors indicates that both of these habitats act as larval reservoirs during the dry season. Presence of theses habitats in close proximity to human habitats create a potential risk of malaria transmission among humans. Therefore, health authorities need to be vigilant on these new habitats in vector control programmes.Item Application of a real time Polymerase Chain Reaction (PCR) assay for the early diagnosis of human leptospirosis in Sri Lanka(Academic Press, Elsevier, 2016) Denipitiya, D.T.H.; Chandrasekharan, N.V.; Abeyewickreme, W.; Hartskeerl, C.M.; Hartskeerl, R.A.; Jiffrey, A.M.; Hapugoda, M.D.Leptospirosis has a major impact on health in Sri Lanka but is probably grossly under-recognized due to difficulties in clinical diagnosis and lack of diagnostic laboratory services. The objective of this study was to establish and evaluate a SYBR Green-based real-time Polymerase Chain Reaction (rt-PCR) assay for early, rapid and definitive laboratory diagnosis of leptospirosis in Sri Lanka. The rt-PCR assay was established and analytical specificity and sensitivity were determined using reference DNA samples. Evaluation of the assay for diagnosis of clinical samples was performed using two panels of serum samples obtained from 111 clinically suspected adult patients. Patients were confirmed as leptospirosis (n = 65) and non-leptospirosis (n = 30) by the Patoc - MAT. Other 16 samples gave ambiguous results. The analytical sensitivity of the rt-PCR was approximately 60 genome copies and no cross-reactivity was observed with saprophytic Leptospira spp. and other pathogenic microorganisms. Based on confirmation with Patoc-MAT on paired samples this corresponds to a diagnostic sensitivity and specificity of 67.7% (44/65) and 90.0% (27/30), respectively. This study showed that rt-PCR has the potential to facilitate rapid and definitive diagnosis of leptospirosis during early phase of infection 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 A Comparative retrospective study of RT-PCR-based liquid hybridization assay for early, definitive diagnosis of dengue(Oxford University Press, 2010) Hapugoda, M.D.; de Silva, N.R.; Khan, B.; Dayanath, M.Y.D.; Gunesena, S.; Prithimala, L.; Abeyewickreme, W.Dengue is an important flaviviral infection in tropical and subtropical regions. Early diagnosis of dengue infection helps in monitoring the disease, determining when hospital admission is necessary and reducing case fatalities. The objective of this study was to carry out a retrospective comparison of an RT-PCR-based liquid hybridization (RT-PCR-LH) assay with PCR amplification, virus isolation and serological techniques for laboratory diagnosis of dengue infection. Amplified products of non-structural 3 gene were hybridized with a mixture of four dengue type-specific DNA probes in liquid phase. The assay was validated in a comparative retrospective study using acute serum samples collected from 119 fever patients with or without dengue, confirmed by haemagglutination inhibition (HAI) assay, the gold standard assay for diagnosis of dengue infection. The RT-PCR-LH assay was highly specific for dengue and, as an early laboratory diagnostic method, had 100% sensitivity in detecting dengue patients confirmed by HAI assay. A high analytical sensitivity of two fluorescent focus units of dengue virus/reaction was achieved. This RT-PCR-LH assay using a single serum specimen offers distinct advantages of specificity and sensitivity over other diagnostic techniques for early definitive laboratory diagnosis of dengue infection when serological methods are of little value.Item Re emergence of Chikungunya virus in South-east Asia: virological evidence from Sri Lanka and Singapore(Cambridge University Press, 2010) Hapuarachchi, H.C.; Bandara, K.B.A.T.; Sumanadasa, S.D.; Hapugoda, M.D.; Lai, Y.L.; Lee, K.S.; Tan, L.K.; Lin, R.T.; Ng, L.F.; Bucht, G.; Abeyewickreme, W.; Ng, L.Chikungunya fever swept across many South and South-east Asian countries, following extensive outbreaks in the Indian Ocean Islands in 2005. However, molecular epidemiological data to explain the recent spread and evolution of Chikungunya virus (CHIKV) in the Asian region are still limited. This study describes the genetic Characteristics and evolutionary relationships of CHIKV strains that emerged in Sri Lanka and Singapore during 2006-2008. The viruses isolated in Singapore also included those imported from the Maldives (n=1), India (n=2) and Malaysia (n=31). All analysed strains belonged to the East, Central and South African (ECSA) lineage and were evolutionarily more related to Indian than to Indian Ocean Islands strains. Unique genetic characteristics revealed five genetically distinct subpopulations of CHIKV in Sri Lanka and Singapore, which were likely to have emerged through multiple, independent introductions. The evolutionary network based on E1 gene sequences indicated the acquisition of an alanine to valine 226 substitution (E1-A226V) by virus strains of the Indian sublineage as a key evolutionary event that contributed to the transmission and spatial distribution of CHIKV in the region. The E1-A226V substitution was found in 95.7 % (133/139) of analysed isolates in 2008, highlighting the widespread establishment of mutated CHIKV strains in Sri Lanka, Singapore and Malaysia. As the E1-A226V substitution is known to enhance the transmissibility of CHIKV by Aedes albopictus mosquitoes, this observation has important implications for the design of vector control strategies to fight the virus in regions at risk of chikungunya fever.