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 Ovi-trap based surveillance for Aedes in dengue endemic Gampaha District, Sri Lanka during rainy season(Faculty of Tropical Medicine, Mahidol University, 2008) Hapangama, H.A.D.C.; Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Benjamin, S.; Abeyewickreme, W.Dengue is endemic in Gampaha District, Sri Lanka. Aedes aegypti and Aedes albopictus have been incriminated as vectors in urban and suburban environments. An ovitrap-based weekly surveillance was carried out to determine the distribution and abundance of Dengue vectors, in six dengue endemic areas; Galudupita, Gongitota, Wanawasala, Kerangapokuna, Mabole and Welikadamulla in the Gampaha District during May and June 2008 in both indoors and outdoors. Galudupita and Gongitota gave the highest ovitrap indices, both indoors and outdoors as 97% and 73% respectively. Of the total positive ovitraps(1320), positivity for Ae. albopictus, Ae. aegypti and both were 63.5%, 32.9% and 3.6% respectively. Highest mean number of Ae. aegypti and Ae. albopictus larvae per ovitrap in both indoor and outdoor ovitraps were observed Galudupita and Gongitota respectively. However, statistical analysis showed that ovitrap index of Ae. aegypti in six study was not significantly different from each other (P > 0.05). Outdoor mean number of Ae. aegypti larvae per ovitrap in Galudupita, was significantly higher than other sites (F=3.587, P=0.012). Indoor Ae. albopictus ovitrap index of Gongitota was significantly higher than of Welikadamula (F=2.59, P=0.046) while outdoor Ae. albopictus ovitrap index of Gongitota and Wanawasala was significantly higher than of Welikadamula F=3.19 P=.0.02). Results irnplicate that Ae. albopictus prefers more vegetation as observed in Gongitota and Wanawasala. In highly populated and urbanized Galudupita, area with less vegetation, Ae. albopictus population was less than Ae. aegypti even outdoors. Study implicates that Ae. albopictus is the predominant indoor and outdoor breeder during rainy season.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.