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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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 control
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.
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.
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.
Entomological assesment of Wuchereria bancrofti transmission following mass treatment in Gampaha District, Sri Lanka.
(Faculty of Tropical Medicine, Mahidol University, 2007) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Abeyewickreme, W.
Global program to eliminate Lymphatic filariasis (Lf) relies mainly on Mass Drug Administration (MDA). Success of filariasis control programs depends on careful monitoring of infection levels in human populations as well as vectors following the introduction of the drug intervention. This study was conducted to assess the current level of Lf transmission following mass distribution of Diethylcarbamazine-Albendazole in the Gampaha district, Sri Lanka. Field study was conducted in 45 sites in all Medical Officer of Health (MOH) areas of the Gampaha district identified by the Anti Filariasis Campaign (AFC) as high risk for bancroftian filariasis. Investigation revealed 42.22% (19/45) of the sites were infested with mosquitoes positive for Wuchereria bancrofti. Only the sites in urban and semi urban areas were positively infested while rural areas were free of infection. An infection rate of 5.26% was observed among the mosquitoes caught from households and the larval density was 8.7 per positive mosquito. According to a study conducted by the AFC in a sample population (14 sites), the prevalence of Lf was 0.038%. Data recorded by the AFC in 1994 indicated that the infective rate, positivity of mosquitoes and microfilaria density were 90%, 3.05% and 23 respectively. The present study confirms that the level of transmission of W. bancrofti has not decreased in the Gampaha district, despite the MDA Programme been implemented since 2002. Therefore, a proper screening-programme combined with anti filarial treatment and. vector control programme is urgently required to minimize filarial morbidity and interrupt filarial transmission within the country.
Patterns of monthly Culex mosquito density variation in Gampaha district, Sri Lanka.
(Faculty of Tropical Medicine, Mahidol University, 2009) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Manamperi, A.; Abeyewickreme, W.
BACKGROUND: The ecology, development, behavior, and survival of mosquitoes and the transmission dynamics of the diseases they transmit are strongly influenced by climatic factors. OBJECTIVE: The objective of this study was to identify the population density variation of Culex mosquitoes within a period of one year in Gampaha district, Sri Lanka together with potential climatic factors that influenced the Culex population density variation. METHODOLOGY: Culex mosquitoes were routinely collected on monthly basis from 9 sites in Gampaha district. Climate data was obtained from the Department of Meteorology. RESULTS: An exponential growth of Culex population densities was observed in all sites starting in December to February during the study period. The maximum density occurred in January and decreased from March until July. It again increased during August and thereafter decreased until December. Among the study sites the maximum Culex density (mosquitoes/man-hour) was observed in Hekiththa ranging between 89 to 22 and the minimum was from Kurukulawa ranging from 6 to 1. Climatic data suggest that temperature is a limiting factor for the Culex population growth while it was strongly influenced by the rain fall pattern. DISCUSSION: Similar Culex population density variation pattern was observed in all sites but exhibited enormous variation between sites, probably due to different local conditions. Also it was suggested that estimation of W, bancrofti transmission levels in Culex mosquitoes should be practiced in field settings where high mosquito density was observed. Since mosquito density appears difficult to be analyzed by individual dissection use of pool-screen PCR-ELISA would be a better method.
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.
Polymerase Chain Reaction and mosquito dissection as tools to monitor filarial Infection levels following mass treatment in Gampaha District, Sri Lanka
(Elsevier, 2008) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Manamperi, A.; Bandara, K.B.A.T.; Liyanage, T.; Abeyewickreme, W.
BACKGROUND: Mass Drug Administration (MDA)-based Global Lymphatic filariasis (Lf) eradication programmes are aimed at stopping transmission of Wuchereria bancrofti by its mosquito vector. The study was designed to compare one year post treatment (mass distribution of Diethylcarbamazine-Albendazole) infection rates of Wuchereria bancrofti in Culex quenquifaciatus, the main vector of Lf in Sri Lanka using Conventional dissection techniques and a Polymerase Chain Reaction (PCR) assay based on parasite specific Ssp1 repeat which amplifies a fragment of 188 bp. METHODS: Field study was conducted in 45 sites in all Medical Officer of Health (MOH) areas in the Gampaha district, Sri Lanka; identified by the Anti Filariasis Campaign (AFC) as having high-risk for bancroftian filariasis transmission. Indoor-resting mosquitoes were collected by aspiration from 20 houses per each site. Part of the mosquitos were used for dissection and the remainder was used for PCR to detect the filarial parasites in mosquito. RESULTS: Mosquito dissection data revealed 42.22% (19/45) of the sites were infested with mosquitoes positive for Wuchereria bancrofti, indicating 8 transmission active MOH areas (53.33%; 8/15). An infection rate of 5.26% was observed among the mosquitoes caught from households and the larval density was 8.7 per positive mosquito. PCR investigation revealed that 46.67% (21/45) of the sites were positive for W. bancrofti DNA, indicating 11 transmission active areas (73.33%; 11/15). The PCR was found to be more sensitive compared to microscopy in detecting the filarial parasite in field collected mosquito samples with respect to the MOH areas. CONCLUSION: The PCR technique employed offers scope for detection of the filarial parasites with higher sensitivity and specificity; is efficient and rapid. This technique applied for the first time in Sri Lanka, can be adopted as a diagnostic tool for the detection of filarial parasites in the vector population in surveillance to enable effective control of filariasis in the country. Acknowledgements: Authors acknowledge the WHO/SEARO/TDR (grant no. SN 1152) and University of Kelaniya (Research grant no. RP/03/04/06/01/2006) and to Ms. H.M.Renuka and Mr. H.P.Anura U. Pathirana, Mr. M.I.M.Peris and Mr. Y.L.Rassapana for their support during field study activities. © 2008 Elsevier Inc.
Night blood survey of a selected high-risk population for lymphatic filariasis
(Sri Lanka Association for the Advancement of Science, 2007) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Abeyewickreme, W.; Gunawardena, N.K.; Hapuarachchi, H.A.C.; Abeysundara, S.
Human infection with Wuchereria bancrofti causes a disabling parasitic disease known as lymphatic filariasis, which is a major public health and socio-economic problem in many parts of the world. Little is known about the prevalence of filariasis among high-risk populations for filariasis. Objective of this study was to determine such prevalence of lymphatic filariasis among Mahara prison inmates whom the Anti Filaria Campaign (AFC) has identified as a high-risk group. All inmates of Mahara Prison were screened for Microfilariae (Mf) except those in special cells, by night blood film microscopy to determine the prevalence of infection from February to May 2007. All inmates were males of greater than 15 years. Of the 423 inmates screened, 15 were positive for Mf, giving a Mf positive rate of 3.55% in the study population and a mean Mf density of 5 Mf/60 æl blood, ranging between 4 to 9.2 Mf /60 æl of blood with a standard deviation of 2.49. The highest number of infected inmates was residents of Colombo and Gampaha districts where transmission is currently taking place. This is one of the few studies undertaken to date to determine the prevalence of bancroftian filariasis among inmates of a prison, a neglected population in Sri Lanka. This study indicates that the Mf rate of bancroftian filariasis in this study population is far greater than the 0.18% currently reported in the country. Therefore, an intensive programme is recommended to contain the spread of infection within this study population. For this, a proper screening programme combined with antifilarial treatment and vector control programme is urgently required. Acknowledgements: Authors wish to acknowledge the financial assistance received from WHO/SEARO/TDR (grant no. SN 1152) and University of Kelaniya (Research grant no. RP/03/04/06/01/2006). Authors wish to thank Dr. Ravi Mudaliage, Senior Medical Officer, Prison's Hospital, Mahara, Ragama for his support and encouragement during field study activities. Authors also wish to thank Mr. M. Y. D. Dayanath, Ms. N.M. Ashoka Malanie, Mr. M.I.M.Peris, Mr. Y.L.Rassapana and other staff members of the Molecular Medicine Unit and Department of Parasitology, Faculty of Medicne, University of Kelaniya, Ragama for their assistance
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 acknowledged

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