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This repository contains the published and unpublished research of the Faculty of Medicine by the staff members of the faculty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 Oviposition preferences of dengue vectors; Aedes aegypti and Aedes albopictus in Sri Lanka under laboratory settings.(CABI Publishing, 2018) Gunathilaka, N.; Ranathunge, T.; Udayanga, L.; Wijegunawardana, A.; Abeyewickreme, W.Investigations on oviposition behaviour of dengue vectors are critical for effective controlling of vector breeding. Therefore, the aim of the present study was to determine the oviposition behaviour of dengue vectors, Aedes aegypti and Aedes albopictus in Sri Lanka. Batches of 1000 adult mosquitoes (1 : 1, male: female ratio) housed in rearing cages were used for each experimental setup from Ae. aegypti and Ae. albopictus. Oviposition responses with respect to the size of the ovitrap, colours of the ovitrap, water source, sodium chloride (NaCl) concentration and presence/absence of larvae were evaluated by enumerating the number of eggs laid in the ovitraps. The analysis of variance and cluster analysis were used to investigate the significance in the variations among oviposition. The number of eggs laid by both species were improved with the increasing size of ovitraps. Ae. albopictus indicated the highest mean number of eggs in 0.2% of NaCl than in the ovitraps filled with distilled water. However, the egg laying preference was reduced with increasing salinity in both species. Drain water with low dissolved oxygen (DO) level (0.43 ± 0.12 mg l-1) was the preferred water source for both species, while a significantly high oviposition rate was observed in ovitraps with larvae. Black colour ovitraps attracted the majority of gravid females, while white was least preferred. There were no significant variations among oviposition behaviours of Ae. albopictus and Ae. aegypti. The ability of these vectors to breed in waste water with low DO levels may lead them to attain wide dissemination in the natural environment, enhancing their potential threat to human life.Item Detection of dengue virus in Aedes albopictus mosquitoes by Reverse Transcription Polymerase-Chain Reaction-Liquid Hybridization (RT-PCR-LH) based assay.(Sri Lanka College of Microbiologists, 2003) Hapugoda, M.D.; Gunasekera, M.B.; de Silva, N.R.; Gunasena, S.; Prithimala, L.D.; Dayanath, M.Y.D.; Abeyewickreme, W.Dengue is an important public health problem. In this study an RT-PCR-LH assay was developed for the detection of dengue virus in Ae.albopictus, a vector of dengue. Laboratory bred Ae.albopictus (adults inoculated with dengue prototypes were tested by RT-PCR-LH assay. RT-PCR products of NS3 gene of 4 dengue prototypes were hybridized in liquid phase with 32P) labelled cocktail of dengue serotype-specific ologonucliotides. Semi-Nested-PCR agarose gel electrophoresis (Semi-Nested-PCR-AGE) assay with dengue type specific oligonucliotides was carried out for typing of RT-PCR products. Wild-caught Ae.albopictus (larvae (n=89 pools) and adults (n=69 pools) collected from dengue case reported stations during the period of 1999-2002 were also tested by RT-PCR-LH and typed by Nested-PCR-AGE assay). A DNA band (470bp) specific for dengue virus was observed in all pools of Ae.albopictus (inoculated with dengue prototypes in RT-PCR-LH assay. When RT-PCR products of dengue prototypes inoculated mosquitoes were typed by Semi-Nested-PCR-AGE assay, bands of 169,362, 265, 426 bp sizes corresponding to DEN1, DEN2, DEN3 and DEN4 respectively were observed. The DNA band specific for dengue virus (470bp) was also observed in 6 pools of wild-caught adults in RT-PCR-LH assay. They were found to be infected with DEN3 (265bp DEN3 specific DNA band was detected) by Semi-Nested-PCR-AGE assay. None of the wild-caught larvae showed dengue specific DNA band (470bp) in RT-PCR-LH assay). RT-PCR-LH with Semi-Nested-PCR-AGE assays are useful for the detection and typing of dengue virus in Ae.albopictus. Ae.albopictus (in Sri Lanka is competent in transmitting DEN3 and possibly other serotypes. Detection of dengue virus for the first time in Ae.albopictus in Sri Lanka confirms earlier observations that it may play an important role in transmitting dengue). Acknowledgements: Financial assistance by the International Atomic Energy Agency (Technical Co¬operation grant no SLR/ 06 / 024) and University of Kelaniya (Research grant no RP/03/04/06/01/00) is gratefully acknowledged.Item Silent transmission as a risk factor affecting transmission of dengue fever.(Faculty of Veterinary Medicine and Animal Science, University of Peradeniya, 2007) Hapangama, H.A.D.C.; Hapugoda, M.D.; Gunawardene, Y.I.N.S.; Premaratna, R.; Dayanath, M.Y.D.; Abeyewickreme, W.The global incidence of dengue fever has increased by more than four-folds over the last 30 years, making it the most threatening mosquito-borne viral disease at present. Objective of this study is to determine the role of silent transmission •on' incidence of dengue. A total of 40 households, living within a 300 m radius of seven selected ‘confirmed dengue cases at different dengue high risk localities in Gampaha District were recruited for this study. A minimum of three inhabitants were tested for anti-dengue antibodies using a commercial kit to determine the prevalence of silent transmission on dengue infection in each households. Entomological surveillance was carried out in all seven localities. Out of 40 households, 26 (65%) houses were positive for dengue viral infection. Total of 148 inhabitants (68 Males); mean age; 35.9 years were enrolled. Of the 148, 41 (27.7%) had evidence of exposure to dengue virus [positive for IgM: 28/41(68.4%), IgM'& IgG: 7/41(17%) and IgG: 6/41(14.6%)]. Out of 28 primary infections, 20(71.4%) were asymptomatic. Of the 7 secondary infections, 1(14.28%) was asymptomatic. Of the 6 previous exposures to dengue 4(66.67%) were asymptomatic. Of the 7 localities investigated, 1 had >50%, 4 had >25% and 2 had <25% clustering of cases. Ae. albopictus found in all seven localities and Ae. aegypti found only in two localities. This study suggests presence of silent transmission of dengue virus with a trend towards clustering around cases and also this shows that the presence of vectors increases the incidence of dengue.Item Detection of dengue viruses in vector mosquitoes collected from localities with reported dengue cases in the Gampaha District, 2008-2009(Sri Lanka Association for the Advancement of Science, 2010) Hapugoda, M.D.; Abeyewickreme, W.; Peris, I.; Warakagoda, S.; Perera, V.; Weerasinghe, I.Dengue is an important mosquito-borne flaviviral infection in Sri Lanka. Aedes aegypti is considered as the predominant vector of dengue and Ae. albopictus is considered as a subsidiary vector of dengue in Sri Lanka. Detection of dengue virus in these two vector species is important for control activities. Objective of this study was to examine transmission of dengue viruses by Ae. aegypti and Ae. albopictus mosquitoes in the field. Hundred dengue patients confirmed by both clinically and serologically were selected. Mosquito surveillance was conducted by visiting patient's premise within one week of notification of a case. A buffer zone covering 500 m radius in each confirmed patient's premise was surveyed. Larvae and adults were collected using standard larval surveillance techniques and a back-pack aspirator respectively. Adult and larvae were pooled (1-50 larvae/adult per pool). Single step single tube R -PCR assay followed by Semi-Nested-PCR agarose gel electrophoresis was performed. Ethical permission for this study was obtained from the Ethical Review Committee of the Faculty of Medicine, University of Kelaniya. Informed written consent was obtained from each patient for conducting mosquito surveillance at his/her premise. From 100 confirmed dengue case reported stations, 10% (10/100) and 60% (60/100) pools of Ae. aegypti and Ae. albopictus larvae were collected respectively. Adult mosquito collection showed 8% (8/100) and 30% (30/100) of Ae. aegypti andAe.albopictus respectively. These results showed high density of Ae. albopictus mosquitoes. Dengue 3 viral infection was detected in 1 and 7 pools of Ae. aegypti and Ae. albopictus respectively. Transmission of dengue serotype 3 virus by Ae. albopictus and high density of this species in selected areas were observed. Although Ae. aegypti is still the main vector initiating outbreaks and transmitting the disease in city centers, the possibility of Ae. albopictus playing a major role in this region should not be ignored.Theseadultmosquitoes may acquire dengue viruses through horizontal or vertical transmission. Alargenumber of mosquito pools needed to test for confirmation.Acknowledgements: Financial assistance from the WHO/SEARO (WHO/SEARO SN1167)and technical assistance from the IAEA (IAEA TC SRL TC 5/042) are gratefullyacknowledged.Item Co-existence of double serotypes of dengue in patients of Gampaha District(Sri Lanka Association for the Advancement of Science, 2007) Jayasooriya, D.; Gunawardene, Y.I.N.S.; Hapugoda, M.D.; Premaratna, R.; Manamperi, A.; de Silva, H.J.; Abeyewickreme, W.Dengue virus (DENV) known to cause a productive cytolytic infection in humans exists in four different serotypes Dengue 1 (D1), Dengue 2 (D2), Dengue 3 (D3) and Dengue 4 (D4). Among 4 serotypes of DENV, D 3 thought to be associated with explosive DHF epidemics and severe disease in many countries. Our objective was to determine the prevalence of dengue serotypes in Gampaha District and to correlate them with disease severity. Serum samples were collected from patients who were within 4 days of onset of fever and clinically suspected of dengue according to WHO criteria. Total viral RNA extracted from each serum sample was subjected to RT-PCR followed by a semi-nested PCR using specific primers. Out of 91 samples collected between Nov 2005 and Dec 2006, 16 samples were confirmed positive for DENV RNA by RT-PCR. Our results of multiplex semi-nested PCR indicated that 9/16 (56.25 %) of the positive cases were co-infected with serotype 2 and 3 (D2 & D3), while 4/16 (25%) were infected with D 3 and 3/16 (18.75 %) with D 2. 3/4 of D 3 cases had DHF , 1/3 of D2 cases were DHF while there were no DHF cases among the D2 and D3 co-infected patients. The mean Packed cell Volume (PCV) values of D3, D2 and D2 & D3 co-infected were 53.8 %, 48 % and 39.6% respectively while the mean platelet values of those were 66,000 mm3, 123,000 mm3 and 174.000 mm3 , respectively. Dengue infection by a single serotype is common among patients. Although few cases of co-infection by more than one serotype had been previously reported in a few other countries, this is the first description of simultaneous co-infection by D2 and D3 in Gampaha district. In this limited study we have observed a reduction of disease severity in D2 and D3 simultaneously co-infected patients. Could simultaneous co-infection by more than one serotype or a combination of two particular serotypes have lead to a decrease in disease severity among dengue patients is a matter yet to be studied. Further studies are needed to support these conjectures and to establish the clinical implications of simultaneous co-infection on the prevalence of DHF and disease severity. Acknowledgement: NSF (grant SIDA/2006/BT/02) & IAEA (SRL TC 6/028)Item Effect of silent transmission and clustering of cases on transmission of dengue in Gampaha district(Sri Lanka Association for the Advancement of Science, 2007) Hapangama, H.A.D.C.; Gunawardene, Y.I.N.S.; Hapugoda, M.D.; Premaratna, R.; Dayanath, M.Y.D.; Abeyewickreme, W.Silent transmission of dengue virus and clustering of cases have been suggested as possible factors for the increasing incidence of dengue fever. Objective of this study was to determine the presence of silent transmission and clustering of cases of dengue fever in the Gampaha District. Study was carried out using cluster investigation method. A cluster consists of family members and immediate neighbours (minimum of 20) of a dengue index-case. Serum samples from volunteers were tested for anti-dengue antibodies using Dengue-Duo-IgM/IgG Rapid Cassette (Panbio diagnostics, Australia). Using 7 index cases, 148 volunteers (68 Males); mean age: 35.9 years were enrolled. Of the 148, 41 had evidence of exposure to dengue virus [positive for IgM: 68.4% (28/41), IgM & IgG: 17% (7/41) and IgG: 14.6% (6/41)]. Out of 28 primary infections, 71.4% (20/28) were asymptomatic. Of the 7 secondary infections, 14.28% (1/7) was asymptomatic. Of the 6 previous exposures to dengue, 4 (66.67%) were asymptomatic. There was no significant association between sex and exposure to infection [31% (21/68) males vs 25% (20/80) females, p>0.05] or between sex and occurrence of symptoms among exposed individuals [71% (15/21) males vs 50% (10/20) females, p>0.05]. Older individuals aged over 40 years, were most likely to be asymptomatic than younger persons (94% (14/15 exposed) vs 50% (13/26 exposed), P<0.01). Out of 7 clusters investigated, 1 had >50%, 4 had >25% and 2 had <25% clustering effects. A high proportion of asymptomatic infections were observed among adults over 40 years without gender difference. Study suggests persistence of silent transmission of dengue virus with a trend towards clustering around cases. Acknowledgement: World Health Organization (WHO/SEARO SN1144) and technical co-operation by International Atomic Energy Agency (TC/SRL 06/28)Item Knowledge, attitudes and practices (KAP) on dengue control in Gampaha district.(Sri Lanka Association for the Advancement of Science, 2008) Abeyewickreme, W.; Hapangama, H.A.D.C.; Gunawardene, Y.I.N.S.; Hapugoda, M.D.; Gunawardena, N.K.; Wickremasinghe, A.R.Dengue/Dengue Hemorrhagic Fever (DHF) has become a major public health problem in many parts of the tropics. In Sri Lanka, it is endemic in some parts of the country with outbreaks of dengue/ DHF. The present study was done to assess 1) knowledge regarding dengue among the general population in the district of Gampaha, 2) whether simple preventive measures are being practiced in the community. A cross-sectional survey was conducted in selected 2000 households in the Gampaha District from June - August, 2007 using a pre-tested structured questionnaire to assess the level of knowledge, attitudes and practices regarding dengue. The majority of the respondents interviewed were females (65.2%). More than 90% have had secondary education (90.2%). The main source of water supply were pipe borne (43.4%) and well water (40.6%). 64.3% households stored water for washing, drinking and cleaning purposes. More than 95% of the respondents had heard about dengue fever and its transmission. 91.3% cited that their main source of information on dengue was from television/radio. 34.3% had either received advice or participated in a training programme on dengue prevention and 7.8% had received support materials. The main preventive measure used to reduce the mosquito nuisance was personal protection with repellents (73.6%). Most of the respondents (56.8%) felt that no action was taken by the government to control mosquitoes. When respondents views were taken, the suggestions made by them to improve dengue control included, fogging (31.8%), educating people (30.5%), treating water (24.3%) and cleaning the environment (19.5%). When questions were directed at possible methods for community participation for dengue control, the majority were in favour of removing solid waste (84.15%), eliminating stagnant water collections (40.7%), removing larvae (8.75%) and covering all the water containers using lids (8.1%). The community had good understanding on dengue and the main source of information was from the electronic media. However it was found that good knowledge itself does not necessarily lead to good practices. The respondents' attitudes were found to be good and most of them were supportive of control measures. Mass media is an important means of conveying health messages to the public, thus research and development of educational strategies designed to improve behaviour and practices of effective control measures through mass media among the community are recommended. Financial support by World Health Organization TDR/WHO Multi Country Study on "Eco-Bio-Social Research on Dengue in Asia" is acknowledged.