ARS - 2011

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Comparison of recombinant protein and cell lysate antigens for detection of anti-chikungunya (CHIK) IgM antibody
(University of Kelaniya, 2011) Athapaththu, A.M.M.; Abeyewickreme, W.; Hapugoda, M.; Khanna, N.; Inouve, S.; Tun, M.M.N.; Gunasena, S.
Chikungunya (CHIK) virus specific antigen which has high specificity and low cross reactivity with other related diseases is required for laboratory confirmation. The objective of this study is to compare two antigens for detection of anti-CHIK antibody. In this study, two antigens (viral cell lysate and recombinant protein) were evaluated for detection of anti-CHIK antibody by using IgM ELISA. A novel recombinant protein antigen was designed based on envelope domain, a critical antigenic region of the major structural protein. This protein was expressed in Escherichia coli and resultant protein was affinity purified and 10mg with >95% of purity per liter of culture was obtained. Cell lysate antigen was prepared using a crude culture fluid. Two antigens were evaluated separately using a panel of well characterized serum samples obtained from the Dept. of Virology (WHO Reference Centre for Viral Reference and Research), Institute of Tropical Medicine, Nagasaki University. A total of 64 serum samples confirmed as positives and 22 confirmed as negatives were used to evaluate the antigens. Specificity and sensitivity of the recombinant protein antigen was 48% and 90% respectively. Specificity and sensitivity of the viral lysate antigen was 17% and 100% respectively. Viral lysate antigens can cause biohazard risk, high production cost and cross reactivity with other organisms of the same genus/family. Recombinant protein antigen which shows high specificity and sensitivity used in this study is important to overcome problems associated with viral lysate antigen. Testing of a large number of samples is needed to reconfirm this finding. Acknowledgment: Financial assistance and technical co-operation by International Center for Genetic Engineering and Biotechnology (ICGEB CRP SRL 08/02), National Science Foundation (NSF/RG/2009/BT/01) and International Atomic Energy Authority (IAEA/SRL/5/042) is acknowledged.
Morphological differences among Anopheles subpictus sibling species B breeding in waste water habitats in Mannar District, Sri Lanka
(University of Kelaniya, 2011) Gunathilaka, P.A.D.H.N.; Fernando, M.A.S.T.; Premasiri, D.S.; Hapugoda, M.D.; Wijeyerathne, P.; Wickremasinghe, A.R.; Abeyewickreme, W.
Anopheles culicifacies and An. subpictus are considered as the principal and subsidiary vector for malaria in Sri Lanka respectively. An. subpictus sibling species B has been specifically implicated in transmitting malaria in the coastal areas in the west coast of Sri Lanka. The main objective of this study was to identify morphological similarities and differences of An. subpictus B, breeding in waste water habitats in Mannar District. Waste water breeding habitats in three sampling sites having a radius of 20 km in Mannar District were studied for one year (June 2010 to July 2011). These sampling sites were Mannar town, Vankalai and Silawathura. Anopheles larvae and water samples were collected from each breeding site. Larvae were reared until the adults emerged and identified to the species level by taxonomic keys. Densities of Anopheles larvae were calculated. Adult An. subpictus were prepared for egg laying. Sibling status was basically determined based on the number of ridges in the floats of egg with reference to the available keys. Further, other morphological characters were also examined. Water samples were checked for fourteen abiotic variables (pH, dissolved oxygen, conductivity, hardness, free Ammonia, total dissolved solids, colour, odour, suspended solids, alkalinity, conductivity, chloride, total iron and salinity). Breeding of Anopheles species in waste water habitats was observed only in Silawathura and Vankalai sampling sites. A considerable number of Anopheles larvae were collected (n=1197): An. subpictus (96.6%), An. nigerrimus (2.25%), An. barbirostris (0.67%) and An. pallidus (0.5%). According to standards available for surface waters, qualities of water in selected habitats were in the ranges of third class quality. Egg character based on similarities in number of ridges in the egg, all An. subpictus belong to sibling species B. Although they belong to the same sibling species, they showed some morphological differences in their proboscis and palps. Some mosquitoes showed stunted lebellum in the proboscis and their palps had extended more than the length of proboscis (n= 632). Other members had extended lebellum in their proboscis compared to the length of pals (n=357). With ecological changes mosquito sibling species may shift their breeding habitats in order to reduce competition and to attain a wide dissemination in the environment. It is difficult to determine sibling species status using morphological characters. The existing morphological variations and their use for identifying closely related anopheline mosquitoes, especially when they exist as species complexes, are imprecise and need to be replaced with DNA sequence-based techniques.
Study on house dwelling Anopheline species in Batticaloa District, Sri Lanka
(University of Kelaniya, 2011) Fernando, M.A.S.T.; Gunathilaka, P.A.D.H.N.; Hapugoda, M.D.; Abeyewickreme, W.; de Silva, B.G.D.N.K.; Wijeyerathne, P.
Even though the malaria cases are less, vectors which transmit the disease are still present. No proper vector surveys have been carried out in the eastern area of Sri Lanka for more than 30 years, due to the ethnic conflict. The objective is to study house dwelling Anopheline densities to assess the risk of malaria prior to eliminating malaria, and implementing vector control strategies. Surveillance was preformed from July 2010 to December 2010 in 3 selected areas (i.e. Mandur, Vakanery, and Vakarai) in Batticaloa District. Each area was divided into 4 sub sampling sites attaining a total of 12 sub sites in order to ensure full coverage of the whole district. Hand Catch and Window Trap collections were continued to collect mosquito specimens from 44 randomly selected houses in each sub site (n= 528) on a weekly basis. Mosquito densities for each collected Anopheles species were calculated as density per man hour and density per trap for both Hand Catch and Window Trap Collection respectively. Four species were recorded from Hand Catch (i.e. An. barbirostris (0.002), An. nigerrimus (0.081), An. subpictus (1.813) and An. vagus (0.005)). Four species observed from Window Trap Collection (i.e. An. nigerrimus (0.067), An. subpictus (0.700), An. vagus (0.010) and An. varuna (0.174)). An. subpictus, the secondary vector for Malaria in Sri Lanka was predominant throughout this study. The presence of some Anopheline mosquitoes which can act as potential malaria vectors may cause malaria epidemics in these areas. Hence, it is essential to continue more surveillance related to Larval and Trap collections to get the entire picture of Vector composition and prevalence in Batticaloa District.