Conference Papers
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This collection contains abstracts of conference papers, presented at local and international conferences by the staff of the Faculty of Medicine
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Item Male isolation of dengue vector Aedes mosquitoes for sterile insect technique by spiking blood with ivermectin(Sri Lanka Association for the Advancement of Science, 2015) Abeyewickreme, W.; Wijegunawardana, N.D.A.D.; Ranathunge, R.M.T.B.There is an increasing demand for exploration of the potential for applying the Sterile Insect Technique (SIT) in area-wide integrated vector management (AW-IVM) in many countries. However, because female mosquitoes, unlike male mosquitoes, can transmit disease, means to eliminate them from the mass production process are a critical pre-requisite. In addition, the efficiency of the SIT programme could be increased by not releasing female mosquitoes due to the fact that sterile males can then only focus on wild females to achieve mating. Therefore, mosquito SIT programmes success will depend on exclusive release of sterile males, which is impossible on a large scale without efficient sex separation methods. Many different sex separations for different stages of mosquitoes are currently being attempted to successfully establish a sexing mechanism for the above purpose. Among them, the mostly attempted methods broadly include genetic sexing methods, molecular methods, mechanical methods and behavioral methods. For all blood feeding mosquitoes, sex separation could occur at the adult stage by spiking blood with insecticides (malathion, dieldrin) or other mosquito toxins (ivermectin, spinosad), as behavioral tools. In this study, a veterinary preparation of ivermectin (Ivotec,1% w/v) which is used to treat dogs infested with the filarial worm Dirofilaria repens in Sri Lanka was used as a tool for sex separation of adult Aedes albopictus and Aedes aegypti mosquitoes by feeding on spiked blood. In an initial attempt by spiking blood with 5 parts per million (5 ppm) ivermectin, 40% of the blood–fed females could survive beyond 24 hours post feeding. However, when the dosage of ivermectin was increased to 7 ppm the survival rate decreased below 40%. Since there had been high mortality of both females and males even in the control cages in which mosquitoes were blood-fed without ivermectin it was suggested that the age of the mosquitoes used may be a factor for high mortality of mosquitoes in the control experiment. When the experiment was repeated with 7 ppm ivermectin in blood using 4-5 day old mosquitoes more than 65% mortality could be observed within 12 hours post feeding in the experimental cage with a significant difference in mortality compared to the controlItem Knowledge and practices of dengue control and their effect on breeding sites and vector populations(Sri Lanka Medical Association, 2010) Pinidiyapathirage, M.J.; Gunethilake, M.A.G.N.; Wijegunawardana, N.D.A.D.OBJECTIVE: To describe the association between knowledge and practices of dengue control with the observed dengue breeding sites and vector populations in a community. METHODS: A cross-sectional survey was conducted among households in Negombo area in July 2009 during the height of the dengue epidemic in the country. Knowledge and practices in this community were measured using two methodologies. The first was a questionnaire, to be answered by the household respondent; the second, a mosquito larval survey, to identify potential and actual mosquito breeding sites in the corresponding household. The use of the two instruments allowed comparison of respondent knowledge and reported practice with the actual condition of the compound. RESULTS: All respondents (n=120) have heard of dengue, 89% knew at least one symptom of dengue and 93% knew that a mosquito was responsible for transmission. 60% correctly stated the preferred biting times of the vector and 80% knew that discarded tyres, bottles and plastic containers with water collections were the potential vector breeding sites. On inspection, 104 (87%) households had at least one potential breeding source. However, Aedes aegypti/albopictus larvae/pupae were observed only in water samples collected from 3 (2.5%) households. Knowledge about dengue symptoms, methods of prevention or level of education had no association with the potential breeding sites found. Low income was significantly associated with having at least one potential breeding source in the household. CONCLUSION: Although the level of knowledge about dengue was high in this community, we found only httle evidence that this knowledge was put into practice.Item Impact of repeated annual Diethylcarbamazine-Albendazole mass treatment on transmission of Wuchereria bancrofti in the Gampaha district.(Faculty of Veterinary Medicine and Animal Science, University of Peradeniya, 2007) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Abeyewickreme, W.Entomological and parasitological surveys are critical for the baseline evaluation of impact of repeated annual. Diethylcarbamazine-Albendazole mass treatment on the reduction of microfilaria density and level transmission of Wuchereria bancrofti in Culex quinquefaciatus. The objective of this study was to assess the current situation, following the mass drug administration programme in the Gampaha district, with regard to lymphatic filariasis, using entomological and parasitological data. A pilot survey was carried out using parasitological, 'clinical and entomological indicators in 21 sites in 7 Medical Officer of Health areas of Gampaha district to assess the current filariasis situation. The localities were selected from. the Medical Officer of Health areas based on previous data obtained from the regional Anti Filariasis Campaign office. Results indicate that 76.19% (16/21) sites were infested with mosquitoes positive for Wuchereria bancroft and the positivity of 1.44% (31/2157) was observed among the mosquitoes caught from households in the selected sites. The microfilariae wasa determined to be 15.5 per positive mosquito. The parasitological result was indicated 0.017 % prevalence of lymphatic fllariasis in the selected population. Data recorded by the Anti Filariasis Campaign Gampaha in 1994, suggested that significant decrease of infective rate, positivity of mosquito and microfilaria density, which are respectively 90%, 3.05% and 23. Study confirms that active transmission of Wuchereria bancrofti is currently taking place in the Gampaha district, despite, the mass drug administration Programme been implemented since 2002. This study highlights the urgent requirement of a proper screening programme combined with anti filarial treatment and vector control programme to minimize filarial morbidity and interrupt filarial transmission within the country.Item GIS mapping of Lymphatic Filariasis endemic areas in Gampaha district, Sri Lanka; based on the epidemiological and entomological screening(Faculty of Tropical Medicine, Mahidol University, 2009) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Manamperi, A.; Abeyewickreme, W.BACKGROUND: The health issues related to vector borne diseases appear always to be related to space and time. Therefore it is ideal to link Geographical Information Systems (GIS) with epidemiological and entomological data to monitor spread of infection and target control strategies. OBJECTIVE: The objective of this study was to develop a site directed GIS map for lymphatic filariasis (Lf) dispersed areas in Gampaha district, Sri Lanka as a guide to target control activities. METHODOLOGY: Epidemiological and entomological screening of Lf was done in nine pre-identified endemic areas in Gampaha district, using night blood screening and pool-screening PCR-ELISA protocols respectively. RESULTS: Overall, 1073 (286 children, 787 adults) from 9 sites were examined. Mf-positive cases were detected in 2 sites, with a prevalence rate of 10.5% (Hekiththa) and 3.4% (Peliyagoda) with over 30% Mf prevalence in adult mosquito populations. The overall prevalence of mosquitoes with L1-L2 larvae of W. bancrofti ranged from 0%-8.54% by dissection and point estimates of infection prevalence, as assayed by PCR-ELISA, ranged from 0% - 35.4%. According to geographical data, the highest number of cases was found at altitudes between 2.5-3.5 m and highly populated areas where transmission appears to be taken place. Questionnaires indicated limited community awareness can be a reason for the fairly static infection rate prevalent in Peliyagoda sentinel site. DISCUSSION: The maps derived indicate the substantial extent as well as the marked variability in the geographical distribution of Lf in Gampaha, demonstrating site related trends.Item Large-scale entomological assessment of Wuchereria bancrofti transmission by dissection and PCR-ELISA in Gampaha district, Sri Lanka(Sri Lanka Association for the Advancement of Science, 2008) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Manamperi, A.; Hapuarachchi, H.A.C.; Bandara, K.B.A.T.; Abeyewickreme, W.Entomological surveys are important tools for monitoring progress of lymphatic filariasis (Lf) eradication programs. In this study, dissection of Culex quinquefasciatus was compared with a Polymerase Chain Reaction - Enzyme Linked Immunosorbent Assay (PCR-ELISA) for pooled mosquitoes to assess filarial infection levels in the major vector of Wuchereria bancrofti in Gampaha district, following mass-treatment programme with diethylcarbamazine (DEC) and albendazole. Mosquitoes were collected in 30 sentinel and 15 non-sentinel sites in 15 Medical Officer of Health (MOH) areas of Gampaha district known for the presence of W. bancrofti transmission. Captured mosquitoes were dissected to determine the W. bancrofti larvae (L1, L2, L3). PCR was carried out using Deoxyribonucleic acid (DNA) extracted from mosquito pools (15 body parts/pool) utilizing primers specific for the Wb-SspI repeat. PCR products were analyzed by hybridization ELISA using fluorescein-labeled wild type specific probes. The prevalence of infected/infective mosquitoes in PCR pools (3pools/site) was estimated using the PoolScreenTM algorithm and a novel probability-based method. The prevalence of infected mosquitoes with L1-L2 larvae of W. bancrofti ranged from 0%-8.54% by dissection and point estimates of infection prevalence as assayed by PCR-ELISA, ranged from 0% - 25.4%. Mosquitoes collected from all MOH areas (80%, N = 12), except for Minuwangoda, Dompe and Ragama, were positive for W. bancrofti larvae, with a prevalence rate ranging from 0.78% to 16.97% in both methods. Of 30 sentinel sites, 43.3% (N = 13) were positive for W. bancrofti transmission whereas it was evident in 40% (N = 6) of non-sentinel sites. The proportion of positive pools detected by the PCR-ELISA assay was higher than that obtained by the dissection indicating that PCR-ELISA assay is more sensitive than the dissection method in detecting infected/infective mosquitoes. Also results of this study showed that autochthonous transmission of W. bancrofti continues in the Gampaha district despite completion of the 5 year mass drug administration (MDA) programme. Therefore, we emphasize the use of more sensitive tools such as PCR-ELISA to monitor the impact of the MDA programme on disease transmission. This study also emphasizes that control measures should be further continued until the microfilareamic population is reduced to a level which could interrupt transmission in the area. Financial assistance received from WHO/SEARO/TDR (grant no. SN 1152) and University of Kelaniya (Grant no. RP/03/04/06/01/2006) is acknowledgedItem Comparison of five DNA extraction methods from human blood for the detection of Wuchereria bancrofti by polymerase chain reaction assays(Sri Lanka Association for the Advancement of Science, 2008) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Manamperi, A.; Hapuarachchi, H.A.C.; Gunawardena, N.K.; Abeysundara, S.; Abeyewickreme, W.Introduction: Lymphatic filariasis (Lf) is the second most common vector-borne disease globally. Approximately 90% of global burden of Lf is caused by Wuchereria bancrofti. W. bancrofti is routinely diagnosed by morphological identification of microfilariae (Mf) by microscopy which is a labour intense, low sensitive and time consuming method. Detection of W. bancrofti Deoxyribonucleic acid (DNA) using polymerase chain reaction (PCR) technique has become popular today, because of its high sensitivity and specificity. The overall success of the PCR strategy in detecting a filarial parasite in human blood varies between sample preparation methods. The objective of this study was to compare five DNA extraction methods (Lysis + centrifugation, Chelex method, Mf pellet method, Q1Aamp DNA Mini Kit commercial system, and Phenol-chloroform) with regard to duration of completion, labor involvement and PCR analytical sensitivity in-relation to DNA quality and quantity for the detection of W. bancrofti in human blood. Five blood samples positive for mf of W. bancrofti were tested for each DNA extraction method and were compared with respect to the sensitivity, time and quality/quantity of DNA and also by PCR analysis. Of the 5 methods tested, Mf pellet method was found to be the most simple and effective technique for the isolation of W. bancrofti Mf in human blood. This method was quick (15 min to complete), simple (5 min of manual labor), and very economical. It does not require any organic solvents, and the entire extraction procedure uses only two steps requiring supernatant transfer between tubes, hence minimizing the possibility of cross-contamination. Moreover, the PCR analytical sensitivity of the Mf pellet method was comparable to that of the commercial kit used. No PCR inhibitors were detected, independently of Mf count in the blood. Same method (optimal DNA extraction method) can be also used for the detection of parasite DNA from the field collected Mf positive mosquitoes using a PCR. Therefore, we recommend the Mf pellet method for processing large numbers of blood samples in community surveys aimed at determining the prevalence of W. bancrofti infection.Item Efficacy and potential use of VectoBac WGr for the control of Culex quinquifaciatus mosquitoes in three different localities of Gampaha district, Sri Lanka(Sri Lanka Association for the Advancement of Science, 2009) Wijegunawardana, N.D.A.D.; Hapangama, H.A.D.C.; Gunawardene, Y.I.N.S.; Manamperi, A.; Abeyewickreme, W.Some methods of mosquito population control, especially the application of pesticides for adult mosquitoes, can have an impact on the environment and individuals with a heightened sensitivity to pesticides. Of the available control tools, biological controls are considered to be generally host-specific and environmental friendly. Although biological controls are not feasible on a large scale, they are often very effective in localized areas. Therefore, efficacy and potential use of water dispersible granular (WDG) formulations of bacterial larvicide, Vectobac- WGr (Bacillus thuringiensis israelensis [Bti]) (Valent BioSciences Cooperation in USA) was tested against Culex quinquefasciatus in three selected localities in the district of Gampaha. Pre-treatment, treatment and post-treatment adult C. quinquefasciatus mosquito densities were recorded for 20 consecutive days within the study period between May to December 2008. The study period covered both rainy and dry seasons. The larvicide was applied to three selected treatment sites and three control sites with a backpack sprayer to test the efficacy of Bti treatment. The six Pre-treatment surveillances in the three treatment and three control sites were done once a week in the first month and once in two weeks for the second month. Adult mosquitoes collected were identified in the laboratory to the species level and the numbers were recorded. For each site, 30 households were selected, with a total of 180 households. During the first month, treatment and surveillance cycles were carried out at weekly intervals, and once in two weeks during the next two months. Six posttreatment surveillances were carried out in the same way as the pre-treatment surveillances. According to the results obtained in this study, out of three treatment sites, two sites were shown to have Culex mosquito density reduction of 19% and 4%, while an increase in mosquito density was observed in the third site. Further, the three control sites, showed an average of 17% mosquito density reduction even without the application of Vectobac-WGr treatment. These results suggest that the product Vectobac-WGr is not effective on Culex quinquefasciatus as a larvicide to control filariasis in Sri Lanka.Item Lymphatic filariasis in selected endemic communities in Gampaha district, Sri Lanka(University of Kelaniya, 2009) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Manamperi, A.; Abeyewickreme, W.Background: Epidemiological surveys are important tools for monitoring progress of lymphatic filariasis (Lf) eradication programs. Objective: The objective of this study was to identify the current status of Lf in Gampaha district, following the completion of 5 year mass-treatment program (MDA), by using traditional night blood screening test. Study design: Study sites were selected within the Lf endemic area while following guidelines of Anti Filariasis Campaign and study population consist of all individual living within the 500 m radius randomly selected land area. Methodology: Night blood screening was carried out between May to August 2009 in 9 sites in 3 closely situated Medical Officer of Health (MOH) areas of Gampaha district. All participants were screened for Microfilariae (mf) after examination by a medical officer for clinical manifestations of Lf and the awareness and practices of participating individuals of >15 years with regard to MDA programme surveyed using an interviewer administrated structured questionnaire. Results: Of the 1073 participants (286 children, 787 adult) screened, 6 were positive in 2 sites for mf, giving mf positive rates of 0.5% and 3.4% respectively in Hekiththa and Peliyagoda sites. While giving mean mf density (mf/60 μl blood) of 2 and 7 respectively. Questionnaire analysis revealed that, of the 1073 participants, 78% were aware of MDA and from that 65% had received the drugs and from that nearly 50% had taken the drugs. Out of those 50%, only 34% had taken it continuously all five years. According to the clinical investigation of 1073 participants, 7%, 3% and nearly 1% had symptoms of headlice, Lyphoedema and Hydrocoela respectively. Discussion: mf rate of Lf in this study population is greater than the currently reported in the country (0.18%). Therefore, an intensive MDA programme is recommended to contain the spread of infection.