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This repository contains the published and unpublished research of the Faculty of Medicine by the staff members of the faculty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 Comparative analysis of the larvicidal activity of temephos (EC50) and novaluaron (EC10) to control Anopheles stephensi in Sri Lanka(Elsevier, 2023) Jude, J.; Gunathilaka, N.; Udayanga, L.; Fernando, D.; Premarathne, P.; Wickremasinghe, R.; Abeyewickreme, W.Background: Anopheles stephensi was first recorded in the coastal area of Mannar District, Sri Lanka, in December 2016. Since then, this vector has been isolated from other districts in the Northern and Eastern Provinces of Sri Lanka. Chemical control is the main arm of vector control that can be used to reduce the vector densities within a short period. Thus, the present study aimed at evaluating the efficacy of using selected insecticides for the control of An. stephensi larvae. Method: The third and fourth instar larval stages of An. stephensi (F2 generation) of field mosquitoes that were caught using cattle baited net trap collections from Columbuthurai, Kurunagar, and Navanthurai areas in Jaffna District, Sri Lanka, were obtained from the laboratory colony established at Jaffna. Batches of 100 larvae were taken for experiments and introduced separately to a concentration series of temephos and novaluron (0.04-400 ppm). A control test was also performed at each setup without introducing insecticides. The mortality rates of An. stephensi larvae exposed to different concentrations of larvicides were recorded at 1, 24 and 48-h intervals. The experiment was replicated five times at individual concentrations for each selected chemical. Data were analyzed using the General Linear Model (GLM) and Probit analysis. Results: The highest mortality rate (100%) at a 1-h exposure period was observed from temephos at >100 ppm. The mortality rates varied significantly for different concentrations and larvicides (p < 0.05). At 24-h of the exposure period, the 100% mortality of An. stephensi larvae were observed from both temephos and novaluron even at 0.04 ppm. Conclusion: Both temephos and novaluron reported 100% mortality rates in An. stephensi larvae at 1-h and 24-h exposure periods. Based on the findings, temephos and novaluron can be recommended as effective larvicides for chemical-based control of An. stephensi in Jaffna, Sri Lanka. Further, it is recommended to conduct a field-based study, where habitat types and water quality are highly heterogeneous and may affect the residual activity.Item Biology, bionomics and life-table studies of Anopheles stephensi (Diptera: Culicidae) in Sri Lanka and estimating the vectorial potential using mathematical approximations(Elsevier, 2023) Jude, J.; Gunathilaka, N.; Udayanaga, L.; Fernando, D.; Premarathne, P.; Wickremasinghe, R.; Abeyewickreme, W.Background: Anopheles stephensi is an invasive mosquito in Sri Lanka that can potentially transmit malaria. The transmission intensity is linked with biology, bionomic and behavioral aspects of a vector that are associated with the Vectorial Capacity (VC). However, the influence of larval conditions eventually affects the vectorial potential of An. stephensi are not well understood. Methods: A colony of An. stephensi was established at the Regional Centre of the Open University of Sri Lanka, Jaffna District. The colony was maintained under confined conditions according to standard protocols. Biotypes of An. stephensi were characterized by referring to the number of egg ridges. Information on (a) biological aspects of eggs (duration for egg hatching, egg development and hatchability), (b) larval development time, larval survivorship pupation success, resting depth of larvae), (c) pupae (adult emergence rate, average time for adult emergence) and (d) adults (biting frequency, mating success gonotrophic cycle, fecundity, duration for egg-laying, percentage of sexes, adult survival/longevity) were evaluated under life-table analysis. Further, selected morphometric characters of each life cycle stage were recorded from the eggs (length and breadth), larvae (head length, width of head, length of thorax, width of thorax, length of abdomen, width of abdomen, and the total length of larvae), pupae (cephalothoracic length and width) and adults (length & width of wing, thorax and abdomen). The VC was calculated using a mathematical-based approach. Descriptive statistics, General Linear Model (GLM) and independent-sample t-test were used for the statistical analysis. Results: All three biotypes were identified based on egg morphology. Mysorensis biotype (47%; n = 470) was predominant followed by type (38.1%; n = 381) and intermediate (14.9%; n = 149). The mean egg length (F(2,997) = 3.56; P = 0.029) and breadth (F(2,997) = 4.57; P = 0.011) denoted significant differences among the three biotypes. The mating success of females observed was 80.7 ± 4.45%. The mean hatching period was 1.9 ± 0.03 days, with a hatching rate of 86.2 ± 0.77%. Overall, 8.0 ± 0.14 days were required for larval development and 30.3 ± 0.14 h were spent in the pupal stage. The pupation success was 94.5 ± 0.37%, and the majority were males (53.1 ± 0.73%). The mean fecundity was 106.5 ± 6.38 eggs and a gonotrophic cycle of 3.4 ± 0.06 days. The female survival rate was 43.2 ± 2.4%, with a mean biting frequency of 66.6 ± 3.5%. The average VC of adult An. stephensi was estimated to be 18.7. Conclusions: The type biotype, which is an effective vector in the Indian subcontinent is present in Sri Lanka. According to the mathematical approximation, An. stephensi found locally has a vectorial capacity of over 18. Therefore, this study warrants the health authorities and vector control programmes to continue the entomological surveys, monitoring of vector densities and implementing appropriate vector control interventions based on biology and bionomic information of vectors.Item Developmental responses and survival of Anopheles stephensi larval stages at different salinity levels(Royal Society of Tropical Medicine and Hygiene, 2022) Jude, J.; Gunathilaka, N.; Udayanaga, L.; Fernando, D.; Premarathne, P.; Wickremasinghe, R.; Abeyewickreme, W.BACKGROUND: Anopheles stephensi is a newly invaded vector in Sri Lanka. It has been identified in coastal areas in the northern and eastern parts of the country and evidences the ability to breed in brackish water environments. METHODS: Laboratory investigations were conducted with batches of 100 first and third instar larvae exposed to a salinity gradient (0-40 ppt). Survival rates at 1 h, 24 h and until pupation were recorded for first and third instar larvae at different salinity levels. The experiment was repeated four times for both instars. Data were analysed using the general linear model and probit analysis. RESULTS: Significant variations in adult emergence were observed from both larval stages at different salinity levels (p<0.05). The highest pupation rates were observed at 2.5 ppt salinity. The survival rate of first instar larvae after 24 h of salinity exposure was >80% up to 12.5 ppt, while 100% mortality was observed for from the ≥25 ppt level of salinity. More than 90% of the third instar larvae pupated from salinity levels <15 ppt. The lowest survival rate was reported as 15.8±2.47% at 25 ppt. CONCLUSIONS: This indicates a high potential of increasing density of A. stephensi in coastal ecosystems in lagoons and other saline water bodies. Hence it is high time to redesign vector control interventions for vector breeding in coastal ecosystems.Item Breeding habitat distribution of medically important mosquitoes in Kurunegala, Gampaha, Kegalle, and Kandy districts of Sri Lanka and potential risk for disease transmission: A Cross-sectional study(Hindawi Pub. Corp., 2020) Ranasinghe, K.; Gunathilaka, N.; Amarasinghe, D.; Udayanga, L.ABSTRACT: Some arbovirus infections, especially dengue, have increased rapidly over the last few decades in Sri Lanka. Prevalence and distribution of different mosquito species have been limitedly documented, which remains grossly inadequate in providing evidence for potential health risks. In this study, the diversity and species composition of mosquitoes in four selected districts in Sri Lanka (Kurunegala, Gampaha, Kegalle, and Kandy) were investigated. Entomological surveys were conducted from a total of 160 temporary and permanent mosquito breeding habitats identified in the study area from June 2017 to October 2018. Mosquito immature stages were sampled using standard dipping, siphoning, or pipetting methods and identified up to the species level. Percentage relative abundance and habitat characteristics such as species richness, dominance, and Shannon-Weiner diversity were calculated for each surveyed habitat type. Associations between co-occurring species were estimated by Hulbert's coefficient of interspecific association (C8). A total of 4663 mosquito larvae belonging to seven genera and fifteen species of mosquitoes were collected. The relative distribution of mosquito species differed significantly among the four studied districts (X 2 = 143.248; df = 33; P < 0.001). According to Kruskal-Wallis statistics (P < 0.05 at 95% of significance), all diversity indices for immature stages of medically important mosquitoes varied significantly across different breeding sites. Paddy fields had the significantly highest species richness of 4.0 ± 2.82. The coefficients of interspecific association among all the recorded medically important vector mosquitoes were found negative during the present study. The findings of the current study would be useful to identify the entomological potential for disease transmission and facilitate the implementation of appropriate vector control interventions. This would ultimately provide an avenue to improve the personal skills of health staff rather than limiting their knowledge to specified disease vectors, under which the control program is concerned.Item Illustrated key to the adult female Anopheles (Diptera: Culicidae) mosquitoes of Sri Lanka(Springer, 2017) Gunathilaka, N.The identification of adult female anopheline mosquitoes is an important aspect in malaria surveillance and control strategy throughout the world, and taxonomic keys are being regularly revised and updated as new information becomes available. However, the currently available key to the anophelines of Sri Lanka is of limited use, because they were published more than 25 years ago. This paper presents an illustrated key for the identification of 23 adult female Anopheles mosquitoes which are currently recognized as local anopheline species in Sri Lanka.Item Characterization of the sibling species status of Anopheles culicifacies breeding in polluted water bodies in Trincomalee District of Sri Lanka(Sri Lanka Association for the Advancement of Science, 2015) Gunathilaka, P.A.D.H.N.; Prashath, K.; Abeyewickreme, W.Anopheles culicifacies, the major vector of malaria in Sri Lanka, is known to breed in clean and clear water. However, recent findings have confirmed breeding in waste water containing drains. However, no study has been conducted to identify whether it is vector or non vector siblings. Therefore, the objective of the study was to identify the sibling species status of An. culicifacies breeding in waste water containing drains. An. culicifacies adult samples (Reared from larvae) were obtained from the Padavisiripura Entomological team attached to Tropical and Environmental Diseases and Health Associates (TEDHA) Malaria Elimination Program in the Trincomalee District. The collected mosquito specimens were processed for the extraction of genomic DNA individually. The PCR amplifications were carried out using different primer combinations for differentiating species A from D, species B from C, species B from E, and species B, C, and E from each other. The results obtained from the gel electrophoresis were compared with the marker, and band sizes of 359 bp, 248 bp, 95 + 248 bp, 166 + 359 bp and 178 + 248 bp were used to identify the sibling species A, B, C, D and E respectively. The molecular biological identification of the field caught An. culicifacies samples indicated that only 6.25% (1/16) represented sibling species B. About 93.75% (15/16) of the samples were An. culicifacies sibling species E. According to the results, the majority of the species belongs to sibling species E which is considered as the vector sibling species of An. culicifacies. This is the first time that An. culicifcicies E breeding in waste water was confirmed by a molecular method. However, malaria control programs focus on rural communities as a result of bio-ecology of Anopheles mosquitoes. Therefore, unusual breeding habitats such as waste water collections may mislead the current vector controlling programs. These results reconfirm that An. culicifacies has adapted to breed in water bodies including waste water collections. Since a majority of them belong to sibling E, which is considered as the vector, this may adversely affect the current malaria elimination program. Therefore, new strategies should be adopted to control malaria vector breeding in these unusual breeding habitats under the current malaria elimination program in Sri Lanka.Item Appearance of Anopheles jeyporiensis James from Sri Lanka; a new species to the mosquito checklist(The Japan Society of Medical Entomology and Zoology, 2015) Gunathilaka, N.; Abeyewickreme, W.; Hapugoda, M.; Wickremasinghe, A.R.Previous records of Sri Lankan Anopheles were most imperfect, and even the number and names of the species present were very doubtful. There was no systematic study conducted for Sri Lankan adult anophelines since 1990. Therefore, the objective of this study was to explore the species abundance and morphological variations of anopheline mosquitoes in Sri Lanka. Entomological surveys were conducted on a monthly basis from June 2010 to December 2013 in Trincomalee District, using five entomological techniques. Entomological surveys identified a total of 131,804 mosquito specimens belong to 18 anopheline species. One of which was An. jeyporiensis, a species that was not in the checklist in Sri Lanka. Its basic morphological features are similar to the members in Myzomyia series under the subgenus Cellia. Following characteristics were used to confirm the species as An. jeyporiensis; Centre of the scutum covered with short oblong white scales extending back to scutellum; Vein R 1 usually with accessory pale spot on preapical dark (PD) area; Foretarsomere 1 with apical pale band nearly 2.0 width of tarsomere diameter.Item Breeding habitat diversity and species composition of Anopheles mosquitoes in Trincomalee district, Sri Lanaka(HABITATS Conservation Initiative, 2014) Gunathilaka, P.A.D.H.N.; Fernando, M.A.S.T.; Hapugoda, M.D.; Wijeyerathne, P.; Wickremasinghe, A.R.; Abeyewickreme, W.Entomological studies on the abundance of malaria vector Anopheles mosquitoes have not been studied in some malaria endemic areas of Sri Lanka over past 30 years in view of the security situation. The aim of this study was to explore the habitat diversity and distribution of anopheline species in Trincomalee District in order to prioritize vector breeding habitats for developing timely and cost effective larval controlling measures. Potential larval habitats for Anopheles mosquitoes were surveyed from June 2010 - December 2010, in selected sampling sites in the Trincomalee District; Gomarankadawala, Echchallampaththu, Mollipothana, Thoppur and Padavisiripura, within a radius about 20 km on weekly basis. The species distribution and density were calculated. A total of 3,701 larval specimens representing twelve Anopheles species were reported form 19 breeding habitats (Tank margin, main canal, paddy field, vegetative canal, lake, built well, burrow pit, distribution canal, pond, rock pool, canal, un-built well, common well, river margin, sand pool, animal foot print, rain water collection, quarry pit and marshy land). Ten habitats were categorized under structurally complex group based on the presence of biotic communities. Only An. subpictus can be regarded as constant according to Distribution (C) (C= 80.1-100%).An. nigerrimus, An. peditaeniatus, An. pallidus and An. vagus were frequent (C= 60.1 – 80%). An. varuna, An. barbirostris, An. annularis and An. barbumbrosus were shown as infrequent species (C= 20.1 – 40%) and other namely An. aconitus, An. culicifacies and An. jamesii can be categorized under sporadic appearance (C= 0 – 20%). According to Density (D) criterion, five species (An. subpictus, An. nigerrimus, An. varuna, An. pallidus, An. barbumbrosus) were within the dominant class (D > 5%). Four species (An. vagus, An. peditaeniatus, An. annularis, An. aconitus) were in the subdominant class (1< D <5%). Only An. jamesii and An. culicifacies were the satellite species (D < 1%).Item Breeding of Anopheles culicifacies in different waterbodies in the district of Trincomalee(University of Kelaniya, 2012) Gunathilaka, P.A.D.H.N.; Fernando, M.A.S.T.; Hapugoda, M.D.; Wijeyerathne, P.; Wickremasinghe, A.R.; Abeyewickreme, W.Introduction: Anopheles culicifacies (Diptera: Culicidae), the major vector of malaria in Sri Lanka is known to breed in clean and clear water. This study was focused to understand the larval habitats of the major malaria vector with the eco system changes in the Trincomalee district of the Eastern Province. Method: Potential larval habitats for Anopheles mosquitoes were surveyed on a monthly basis for 17 months (January 2011 –June 2012) in 4 different selected sampling sites (Murthankulam, Kommnaimottai, Paranamadawachchiya and Kokmotawewa). Collected larvae were identified using standard taxonomic keys. The species Distribution (C) and Density (D) were calculated. Results: A total of 2996 larval specimens representing 13 Anopheles species were reported from 16 different breeding habitats namely, waste water (n= 635), built well (n= 1229), earth well (n=149), agricultural well (n=9), rain water collection (n=89), animal hoof print (n=17), burrow pit (n=256), rock pool (n=10), canal (n=15), irrigation canal (n=27), lake margin (n=27), tank margin (n=448), pond margin (n=15), marshy land (n=13), paddy field (n=15) and slow moving water (n=42). An. culicifacies was observed as the most predominant species throughout the survey. According to Density criterion, An. culicifacies (44.0%), An. subpictus (19.2%), An. barbirostris (13.2%), An. peditaeniatus (10.28%) and An. nigerrimus (8.7%) were within the dominant class; (D > 5%). Two species (An. vagus, An. pallidus) were in the subdominant class (1< D <5%). Only An. annularis, An. varuna, An. barbumbrosus, An. pseudojamesi, An. jamesii and An. tessellatus were the satellite species (D < 1%). An. nigerrimus, An. subpictus and An. peditaeniatus can be regarded as constant according to distribution (C= 80.1-100%). Only An. vagus was the most frequently reported (C= 60.1 – 80%) species. All other Anopheles including An. culicifacies were observed as infrequent species (C= 20.1 – 40%) and no species was identified as sporadic appearance (C= 0 – 20%). Most productive breeding site for An. culicifacies were drains covered with waste water (Density= 81.57%) in remote areas. Interpretation & conclusion: These results indicate that An. culicifacies has adapted to breed in a wide range of water bodies including waste water collections although they are considered to breed in clean and clear water. The survival of the major vector mosquito in widespread water bodies could be responsible for the increase in the incidence of malaria in the future.Item Blood-feeding patterns of Anopheles mosquitoes in malaria-endemic areas of Sri Lanka(University of Kelaniya, 2012) Gunathilaka, P.A.D.H.N.; Fernando, M.A.S.T.; Hapugoda, M.D.; Wijeyerathne, P.; Wickremasinghe, A.R.; Abeyewickreme, W.Background: Studies on host preference patterns in blood-feeding of anopheline mosquitoes are crucial for incriminating them as malaria vectors. However, little information is available on the host preferences of Anopheles mosquitoes in Sri Lanka. Therefore, the objective of the present study was to determine the hematophagic tendency of the anophelines. Methods: Adult Anopheles mosquitoes were collected using Cattle Baited Trap Collection (CBTC), Cattle Baited Net Collection (CBNC), Window Trap Collection (WTC), and Hand Collection (HC) from selected sentinel sites in Mannnar (3) and Trincomalee (5) Districts during June 2011- June 2012. Each blood fed mosquito was processed in to 9 cm whatman filter papers within 24 hours after blood meal has taken. DNA was extracted using the dried blood meal protocol of the QIAmp DNA mini kit. A multiplexed, Real Time Polymerase Reaction (RT- PCR) assay targeting 8 animals was developed for two panels (Panel 1: Bovine, cat, pig, monkey: Panel 2: Human, rat, dog, chicken) to identify the host meal of Anopheles. Human Blood Index (HBI), Forage Ratio (FR) and Host Feeding Index (HFI) were calculated. Results: A total of 216 field caught freshly engorged females mosquitoes belonging to 12 Anopheles species was analyzed. The host preference of anophelines observed in this study was bovine (86.17%), human (1.84%), cat (0.46%) and pig (0.46%). Only 6.91 % was positive for both human and bovine. In addition 5.0 % of the total samples tested were unknown. The overall HBI and HFI in the present study were low indicating the humans were not the preferred host for the tested anopheline species. Nevertheless, a small proportion engorged An. aconitus (0.37), An. culicifacies (0.27), An. barbirostris (0.2), An. annularis (0.125) and An. subpictus (0.12), An. peditaeniatus (0.08), An. pseudojamesi (0.04) and An. barbumbrosus (0.04) contained human blood, The FRs for human were <1.0 for most of the anophelines, except An. aconitus (1.04). Conclusion: The presence of human blood, in mosquito species indicates the possibility of them transmitting malaria. Hence, further studies on vector competence are needed to determine the role of each of the above anopheline species currently as efficient vectors of malaria.
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