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This repository contains the published and unpublished research of the Faculty of Medicine by the staff members of the faculty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 Serotype distribution of dengue in Gampaha District, Sri Lanka(Faculty of Tropical Medicine, Mahidol University, 2008) Jayasooriya, D.H.S.W.; Gunawardene, Y.I.N.S.; Manamperi, A.; Hapugoda, M.D.; Premaratna, R.Dengue Virus (DENV) affecting millions of people mainly in the tropical and subtropical regions is a positive sense RNA virus which exists in four different serotypes (DENV1-4) and several subtypes. All four serotypes have been found in Sri Lanka. The objective of the study was to determine the DENV serotype distribution in patients and mosquitoes of Gampaha district. Serum was isolated from acute phase blood samples collected from dengue suspected patients during the febrile period. Mosquitoes were collected from different locations where dengue confirmed cases were reported. Pooled and crushed mosquito heads and serum samples were separately subjected to RNA extraction, RT-PCR, semi nested PCR with Dengue serotype specific primers and solution hybridization with Phosphorous 32 labeled probes respectively. Out of 93 patients, 34 were positive for DENV out of which 19 corresponded to DENV2, 5 to DENV3 and 10 were co-infected with DENV2 and DENV3. Of the positive infections corresponding to serotypes 2, 3, 2-3 co-infected; 7/19 (36.8%), 3/5(60%), 0/10 (0%) had developed dengue haernorrhagic fever respectively Among 14 mosquito pools, 5 were positive of which 3 were infected with DENV2 and 2 with DENV3. It was observed that although both DENV2 and DENV3 circulate among patients and in mosquitoes in Garnpaha District, DENV2 was predominant in both. Only Aedes albopictus 'presence in all localities was significant. A greater percentage of severe form of the disease among DENV3 infected patients was observed while a less severe form of the disease was observed in DENV2 and DENV3 co-infected patientsItem 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)