International Postgraduate Research Conference (IPRC)

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Assessment of artificial blood feeding methods and efficacy of different blood meal sources in mass rearing of Aedes aegypti for innovative vector controlling strategies
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Gunathilaka, P.A.D.H.N.; Ranathunga, R.M.T.B.; Udayanga, N.W.B.A.L.; Abeyewickreme, W.
Background Mass rearing of vector mosquitoes of dengue is a crucial requirement for implementation of innovative vector controlling strategies such as Sterile Insect Technique (SIT), Incompatible Insect Technique (IIT) and transgenic mosquitoes. Selection of the artificial membrane-feeding technique and blood meal source have been recognized as key considerations in mass rearing of vectors. Methodology Three artificial membrane feeding techniques (Glass plate method, Metal plate and Hemotek membrane feeding method) and three blood sources (human, cattle and chicken) were evaluated based on feeding rates, fecundity and hatching rates of Ae. aegypti, under laboratory conditions. One-way ANOVA, cluster analysis, analysis of variance (ANOSIM) and principal coordinates (PCO) analysis, were used to investigate the significance in the variations among blood feeding. Results Feeding rates of Ae. aegypti significantly differed among the membrane feeding techniques as suggested by one-way ANOVA (p <0.05). The metal plate method was identified as the most efficient and cost effective feeding technique. Blood feeding rate of Ae. aegypti was higher with human blood followed by cattle and chicken blood, respectively. However, no significant difference was observed among mosquitoes fed with cattle blood and human blood, in terms of fecundity, oviposition rate and fertility. Conclusions Metal plate feeding technique could be recommended as the most effective membrane feeding technique for mass rearing of Ae. aegypti, due to its high feeding rate and cost effectiveness. Since, obtaining human blood for insectary colony maintenance is problematic due certain ethical issues, cattle blood could be recommended for mass rearing Ae. aegypti.
Assessment of possible social and entomological risk factors affecting transmission of dengue in the District of Gampaha
(Faculty of Graduate Studies, University of Kelaniya, 2015) Withanage, G.P.W.K.; Abeyewickreme, W.; Hapugoda, M.D.
Dengue is the most important mosquito-borne viral infection transmitted to humans in Sri Lanka causing more than 30,000 cases annually. The objective of the study was to identify possible social and entomological risk factors affecting transmission of dengue in Gampaha district where the second highest number of dengue cases recorded during last ten years. Four Medical Officer of Health (MOH) areas were selected based on annual number of dengue cases greater than 250 for last ten years. One GramaNiladhari (GN) division was selected from each MOH area as a study area where the highest number of dengue incidents reported. In each study area, a cluster of 150 households was selected and household and entomological surveys were conducted. The selected areas were Eriyawatiya (Kelaniya MOH), Welikadamulla (Wattala MOH), Akbar town (Mahara MOH), and 3-Kurana (Negombo MOH) GN divisions. There were 2577 population in 600 households in the study areas and 53.5% were females. Average size of a homestead was 17 perches and most of the households (98%-588/600) were individual house. Main vegetations in the homesteads were grass and bushes (97%-583/600) and potential breeding places of dengue vector mosquitoes were observed in 96.1% (577/600) households. Main dengue vector mosquito present in the captured Aedes adult mosquitoes was Aedes albopictusis (92.9%-183/197). Most prominent breeding places were discarded bottles and tins (4.0%-15/371), plant axils (9.7%-36/371), plastic containers (26.4%-98/371), and roof gutters (4.3%-16/371) in the observed premises and 9.2% (34/371) were Aedes larvae positive. Most frequent mosquito preventive measure was bed-nets (30.3%-182/600), but mosquito coils (30.8%-185/600) and vaporizers (17.6%- 106/600) were frequently used. Participants have adequate knowledge about the disease, but they neglect preventive measures and highly depend on government vector control programs. Unplanned households, crowded conditions, poor waste management systems, and negligence to pursue preventive measures may be possible risk factors and therefore, frequent encouragement is needed to control dengue transmission.
Characterization of a Dengue Positive Population in Colombo Municipal Council (CMC) Medical Officer of Health (MOH), Colombo
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Lakmal, M.G.K.; Udayanga, N.W.B.A.L.; Gunathilaka, P.A.D.H.N.; Fernando, S.D.; Karunathilaka, K.; Abeyewickreme, W.
Dengue that has caused 29,777 suspected infections in 2015 has emerged the most challenging health issue faced in Sri Lanka. Approximately 51% of dengue infections are reported from the Western Province. The susceptibility of a population to dengue is influenced by a combination of socio-economic, environmental and epidemiological factors. The current study was conducted to characterize a population of dengue patients residing in a high dengue risk area in terms of their socio-economic appearance. An interviewer administrated questionnaire was used to collect information on the socio-economic aspects of a group of 140 randomly selected dengue positive patients residing in Colombo Municipal Council (CMC) Medical Officer of Health (MOH) area. Out of 140, a majority (63.6%, n=89) were females, while the age groups of 31-40 and 21-30 years were recognized as the most susceptible age groups for dengue. High proportion of the patients (79.3%, n=111) were having an educational level below secondary school (O/L) with a total family income below 20,000 LKR (80.7%, n=113). All the homesteads were smaller (<5 perch) in size, with small roads for access (77.1%, n=108) and/or a footpath (22.9%, n=32) as the access route. Majority of the households (69.3%, n=97) were temporary with moderate conditions (51.4%, n=72), that were mainly utilized for both residential and commercial purposes (63.5%, n=89) at once. In a majority of households’ solid waste was disposed within 7 days (62.1%) via the Municipal Council or by keeping near the main roads (37.9%). Source separation of waste, home gardening and composting by the study population was minimal (n=137, 97.9%). Pipe water remained as the only water source while approximately 27.9% (n=39) households were lacking sanitary facilities. Use of mosquito coils and bed-nets were the most preferred mosquito biting prevention methods. Low educational level, income, poor living conditions and limitations in solid waste disposal methods were recognized as potential risk factors for high infection rates of dengue in this population. Special focus should be given to these key areas by the relevant vector controlling authorities in order to facilitate controlling of dengue outbreaks within the CMC area.
Characterization of Anopheline larval habitats and species composition of aquatic macro-invertebrates in Trincomalee District, Sri Lanka
(Faculty of Graduate Studies, University of Kelaniya, 2015) Ranathunga, R.M.T.B.; Gunathilaka, P.A.D.H.N.; Kannangara, D.N.; Abeyewickreme, W.; Hapugoda, M.D.
Malaria control methods that aim to reduce adult vector populations by targeting their aquatic immature stages. A better fundamental understanding of the biology and ecology of these essential stages could contribute to the implementation of current control methods and to the development of novel strategies. Objective of this study was to examine breeding habitat diversity and analysis of richness, diversity and geographical distribution of Anopheline larvae and the species composition of aquatic macro-invertebrates in their oviposition sites in Trincomalee District. Fifteen major permanent breeding places in five possible malaria sensitive sites (Gomarankadawala, Ichchallampaththu, Mollipothana, Padavisiripura and Thoppur) in Trincomalee District were selected. Anopheles larvae and macro-invertebrates were collected using standard methods for 16 months (April, 2013-July, 2014) and they were identified microscopically. The Shannon diversity index (H') was used to characterize species diversity at the five study sites by its abundance and evenness of the species present. ANOVA were used to analyze the correlation between macro-invertebrates and mosquito larval abundance. In total, 4478 including 11 species of Anopheles larvae were identified. An. subpictus, An. nigerrimus and An. peditaeniatus (71%) were the most abundant and widely-distributed species. Anopheline larval diversity was highest in Mollipothana (H‘=1.986). Whereas in Gomarankadawala, Ichchallampaththu and Thoppur where H‘=1.721, H‘= 0.857 and H‘=0.762 respectively. In total, 28 species of aquatic macro-invertibrates were identified and highest diversity was recorded in Mollipothana, Gomarankadawala and Ichchallampaththu (H‘=3.14-2.56). This deduces that the species richness and diversity of Anopheles mosquitoes and macro-invertebrates are higher in these areas. The presence of permanent breeding places may be the factors for this phenomenon. This study represents the first systematic update to the distribution of macro-invertebrates associated with Anopheles mosquito oviposition sites in Trincomalee District. Knowledge generated on the ecology of Anopheles mosquitoes will help to eliminate malaria vectors in the country.
Determination of appropriate positioning of the ovitraps for dengue mosquito surveillance
(Faculty of Graduate Studies, University of Kelaniya, 2015) Wijegunawardana, N.D.A.D.; Gunawardene, Y.I.N.S.; Chandrasena, T.G.A.N.; Dassanayake, R.S.; Gunathilaka, P.A.D.H.N.; Abeyewickreme, W.
Three months ovitrap survey was conducted to assess the suitable position in placing the ovitraps for dengue vector mosquito surveillance and this study was initiated due to loss of valuable data from our previous studies as a result of physical damage of the ground kept ovitarps. Thirty four households in the Ragama Medical Officer of Health area in Gampaha District were selected to conduct the ovitrap survey during the period of May to July, 2015 to select the most appropriate positioning of the ovitrap. The conventional black plastic ovitraps (3.2x 2.7 cm) were used in this purpose to collect aquatic stages of Aedes mosquitoes while placing plywood paddle (4 x 0.5 cm) over the upper rim of each coded ovitrap. A total of 136 ovitraps were used in the study site providing four ovitraps (2 each indoor & outdoor) for each house while one of the ovitraps of indoor and outdoor being hung and other being kept on the ground. In positioning ovitraps, the outdoor ones were kept 3m away from the house while leaving indoor ovitraps in the living room in close proximity to racks/hanging clothes or partially shaded places. Following collection of samples at each week, ovitraps were washed thoroughly, refilled with new water and a new paddle, and corresponding data were recorded and analyzed. These analyses revealed that number of larvae and the number of Aedes mosquito eggs present in the two different ovitrap positions (Ground kept vs Hung) were not significantly different; in spite of significant difference (P=0.001) between the outside and inside placements. Further, significantly higher values were observed for both number of mosquito eggs and larvae present in each ovitrap kept outside (60 and 13 respectively) than those placed inside (32 and 3 respectively). Furthermore, slightly higher values were observed for hung ovitraps (49 and 9 respectively) than ones kept on the ground (43 and 7 respectively). Finally, ovitrap placed above the ground level was selected in continuing the routine ovitrap survey, as there was considerable reduction of mechanical damage to the latter thus facilitating continuous data collection.
Eliminating female Aedes mosquitoes by spiking blood meals with toxicants as a sex separation method in the context of the sterile insect technique and Incompatible Insect Technique
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Ranathunga, R.M.T.B.; Gunathilaka, P.A.D.H.N.; Udayanga, N.W.B.A.L.; Wijegunawardena, N.D.A.; Abeyewickreme, W.
Ivermectin and spinosad have longevity reducing effects in several insect species, including disease transmitting mosquitoes after feeding blood contaminated with above toxicants on hosts. Therefore, this approach could play an enormous role in mosquito control operations by its use in the female elimination process during mass-rearing, enabling the release of only sterile males in the context of the sterile insect technique (SIT) and incompatible insect technique (IIT) with Wolbachia bacterium. Blood meals of cattle origin were spiked with diffeerenct concentrations (2, 4, 6, 8 and 10 ppm) of Ivermectin (Ivotec, 1% w/v) and Spinosad (Spinosyn, 12% w/v) and offered to a batch of adult Ae. aegypti (n = 300) and Ae. albopictus (n = 300) having 1:1 sex ratio in order to obtain an optimal dose for quick and total female elimination. After 24 hours all remaining females and males were aspirated out and transferred in to new cages separately. An additional blood meal with the initially fed concentrations of ivermectin and spinosad was provided after 24 hours, followed by a 48-hour observation of mortality. This experiment was repeated by feeding cattle blood containing a mixture of ivermectin and spinosad in 1:1 ratio from each concentration. Spiked blood with 8 ppm ivermectin and spinosad killed all the fed females of Ae aegypti and Ae. abopictus within 24 to 48 hours. It was observed that the number of fed females gradually increased, when decreasing the toxicity in combination of ivermectin and spinosad (1:1) in blood for both species. Male mortality did not show any significant differences during the study. Mixed feeding of blood with 8 ppm ivermectin and 8 ppm spinosad have shown as the viable treatment to eliminate female Ae aegypti and Ae. abopictus from laboratory colonies.
Emerging Spatio-Temporal Trends in Dengue Incidence in Poojapitiya Medical Officer of Health (MOH), Central province, Sri Lanka
(Faculty of Graduate Studies, University of Kelaniya, 2015) Udayanga, N.W.B.A.L.; Gunathilaka, P.A.D.H.N.; Iqbal, M.C.M.; Kusumawathie, P.H.D.; Abeyewickreme, W.
Dengue has emerged as one of the major threats to the health sector of many countries including Sri Lanka, due to the increasing number of reported dengue cases over time. Therefore, a statistical and geo-informatics based analysis of the spatio-temporal trends in dengue distribution was carried out to identify recent spatial and temporal trends in dengue distribution patterns, while assessing the susceptibility of the population to dengue infection in the Poojapitiya Medical Officer of Health (MOH) area. Monthly records of reported dengue cases from 2009 to 2013 of the Poojapitiya MOH area were acquired and spatial maps of the recorded dengue case distribution in each Grama Niladhari Division (GND) were developed by using Arc GIS (version 10.2). Normal Chi square test coupled with Paired-Chi square test in MINITAB (version 14.12.0) were used to investigate the impact of gender and age on the infection. Galhinna GND indicated the highest susceptibility to dengue throughout the study period, while the rest of the GNDs indicate less (37 GNDs) or null (29 GNDs) susceptibilities. As suggested by the results of the Paired-Chi square test [>Χ 2 (66, 0.95) = 85.951], the emergence of dengue outbreaks indicated a significantly declining trend in recorded dengue cases in all of the GNDs (regardless of the outbreak in 2012) during recent years. The Percentage Infected Male : Female Ratio (PIMFR) suggested that the, males had a relatively high susceptibility for dengue infection than females with 63.9 : 36.1 of average PIMFER (p=0.00<0.05 at 95% of significance). According to the Paired-Chi square test, the vulnerability of the age groups shifts significantly throughout the study period [>Χ 2 (7, 0.95) = 14.067], where the age groups of 11 - 20 and 21 – 30 indicated high vulnerability to dengue, while >61 age group remained as the least vulnerable group for dengue infection. The identification of the potential high risk GNDs with high susceptibility to the infection of dengue along with the vulnerable age groups in the community would assist the relevant vector controlling agencies to concentrate their efforts, ensuring the effective controlling of dengue outbreak occurrence within the of Poojapitiya MOH.
Evaluation the Oviposition Behaviour of Aedes Aegypti and Ae. Albopictus Mosquitoes; Main and Secondary Vector for Dengue Transmission in Sri Lanka under Laboratory Conditions
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Gunathilaka, P.A.D.H.N.; Ranathunga, R.M.T.B.; Udayanga, N.W.B.A.L.; Abeyewickreme, W.
Studies on the oviposition behavior of Aedes albopictus and Ae. aegypti are critical for effective controlling of dengue vector breeding. However, less attention has been drawn on such aspects of vector biology and bionomics in Sri Lanka. Therefore, the objective of the current study was to evaluate the oviposition behavior of dengue vectors under laboratory conditions. Ovitraps with different sizes, colours, sources of water, sodium chloride (NaCl) concentration (0.2, 0.5, 1, 2 and 3%) and presence and absence of larvae were kept within separate cages of batches of 1000 Ae. albopictus and Ae. aegypti with (1:1, male: female ratio). Female mosquitoes were allowed to lay eggs and the number of eggs laid in different ovitraps were enumerated. ANOVA and cluster analysis were used to investigate the significance in the variations among oviposition behaviours. The mean number of eggs laid by both Ae. albopictus and Ae. aegypti increased with the increasing size of the ovitraps. Ae. albopictus indicated the highest mean number of eggs in 0.2% of NaCl than that of distilled water, while the egg laying preference reduced with the increasing salinity for both species. Drain water with low dissolved oxygen level (0.43 ± 0.12 mg/l) was the preferred water source for both species and indicated a significantly high oviposition rate in ovitraps with larvae. Black colour ovitraps attracted the majority of the gravid females, while white was least preferred. There were no significant variations among oviposition behaviors of Ae. albopictus and Ae. aegypti under laboratory conditions. Back coloured ovitraps were the preferred breeding place.
IGamma- ray irradiation as a method for sterilization of males of Aedes albopictus (skuse) for its control through Sterile Insect Technique (SIT)
(Faculty of Graduate Studies, University of Kelaniya, 2015) Harishchandra, J.; Abeyewickreme, W.; Hapugoda, M.D.; Premaratne, R.G.; Gilles, J.R.L.
Sterile Insect Technique (SIT) can be integrated with other conventional control methods to suppress population of Aedes albopictus, a vector of dengue in Sri Lanka. A study was conducted to determine the effective dose of gamma radiation for producing sterile males of Ae. albopictus mosquitoes. A batch of male pupae (n=32) aged 24-48 hours in F1 was irradiated using Gamma 220, (Co60) irradiator with 25, 30, 40, 50, 60 and 70Gy in duplicates. Adult emergence rate and male longevity were recorded. Virgin females from the same cohort (F1) were introduced into each cage for mating and fed blood starting 5 days after emergence. Then, females were isolated in individual tubes and hatching rate of individual egg batches was calculated after two weeks of egg maturation in hatching solution. Spermacheca of female mosquitoes were dissected and insemination rates were calculated after egg laying. Male mosquito pupae in F1 showed low mortality (0-3.12%) immediately after exposing to radiation (0-48 hours). After 14 days of the irradiation, survival rate of male mosquitoes in F1 were 82.7%, 79.7%, 56.3%, 73.4%, 76.6%, 76.1% and 56.3% when irradiated at 0Gy, 25Gy, 30Gy, 40Gy, 50Gy, 60Gy and 70Gy respectively. No significant difference was observed among survival of males in different doses except in 30 Gy and 70 Gy (Kaplan-Meier survival analysis, Log Rank test). Low survival rate at 30 Gy could be due to mosquito handling errors and need to be retested. Based on the hatching rate of the F2 progeny, males (F1) showed 89%, 93%, 97%, 99%, 99% and 100% sterility when irradiated at 25Gy, 30Gy, 40Gy, 50Gy, 60Gy and 70Gy respectively. Insemination rate of the irradiated males among different doses and controls were above 90% in F1 based on spermatheca dissection of bloodfed females (F1). 50 Gy is recommended as the most suitable radiation dose to produce 99% sterility in Ae. albopictus males which has 76% survival after 14 days of irradiation. This dose can be used to produce sterile males of Ae. albopictus for a SIT programme.
Laboratory Evaluation of the Bio-control Efficacy of Selected Copepods on Dengue Vectors of Sri Lanka
(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Udayanga, N.W.B.A.L.; Ranathunge, R.M.T.; Iqbal, M.C.M.; Abeyewickreme, W.; Hapugoda, M.
Among variety of alternatives for management of dengue vectors, biological control remains as a promising approach, due to its high efficacy, sustainability and low impacts on human and ecosystem health. Copepods are considered asa leading predator of mosquito larvae including Aedes vectors. However, the predatory potential of different copepods on bio-control of dengue vectors has been less studied in Sri Lanka. Therefore, the current study aimed to evaluate the predatory success of five locally abundant copepods on both AedesaegyptiandAe. albopictus. Copepod collections were made from water bodies and rock pools located in the Kandy and Gampaha districts by using a plankton net. After morphological identification, single gravid copepods of different species were used to establish copepod cultures under standard laboratory conditions. Five adult copepods of each species were transferred into containers and groups of 200 first instar Ae. Aegypti larvae were introduced in to each container, separately. The number of surviving larvae in each container was recorded at 3 hour intervals up to 24 hours. Five replicates were conducted for each copepod species. Same experimental design was followed for Ae. albopictus. General Linear Modelling technique (GLM) followed by Tukey’s pair-wise comparison was used to make statistical inferences on the significance of average larvalconsumption rates by studied copepod species. SPSS (version 23) was used for the statistical analysis. Five species of copepods, namely Cyclops languides, C. varicans, C. vernalis, Mesocyclopleuckarti and M. scrassus were considered during the study. Average predation rates of 34.9±1.80 and 33.5±1.06 for Ae. aegypti and Ae. albopictus, respectively, were indicated by M. leuckartias the highest predation rates. Meanwhile, M. scrassus showed the second highest predation rates for both Aedes vectors. On the other hand, the lowest predatory efficacy was shown by C. languides with 10.6+1.60 and 8.4+1.10 for Ae. aegypti and Ae. albopictus, respectively. The average consumption rates of different copepod species varied significantly (p<0.05 at 5% level of significance). The type of Aedes species had a significant influence on the predatory efficacy of studied copepods (p< 0.05) under laboratory conditions. In conclusion, M. leuckartiand M. scrassus that reported the highest predation efficacies on both Aedes larvae could be suggested as potential bio-control agents for dengue vector management approaches in Sri Lanka after semi field and field settings.
Larvivorous Potential of Four Fish Species Against Dengue Vectors in The Kandy District of Sri Lanka
(Faculty of Graduate Studies, University of Kelaniya, 2015) Kusumawathie, P.H.D.; Jayasooriya, G.A.J.S.K.; Gunathilaka, P.A.D.H.N.; Hapugoda, M.D.; Abeyewickreme, W.
There is a growing concern on the effects of insecticides that are used for the control of mosquito vectors of human diseases. Introducing a self propagating predator into the vector breeding habitats may present continual biological control of vector population. In order to control dengue vectors, namely, Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) (Diptera: Culicidae), larval control is one of the major strategies. The objective of this study was to evaluate the larvivorous potential of fish species against dengue vectors. Four fish species, namely, Poecilia reticulata (guppy), Aplocheilus dayi (Udahandaya), Oreochromis niloticus (Tilapia) and Puntius bimaculatus were collected from natural breeding habitats. They were placed in fish stock cement tanks at the Regional Office of the Anti Malaria Campaign in Kandy till they were used for the study that was conducted from January – June 2015. In order to determine the larvivorous potential of the fish species, five fish of each species were placed in separate enamel trays containing de-chlorinated water and allowed to acclimatize for half an hour. Afterwards, a batch of 25 Ae. aegypti larvae was introduced to each tray and counted the number of larvae remaining after 5, 10, 30 minutes, 1 and 24 hours. When all 25 larvae are consumed, another batch of 25 larvae was introduced to those trays and this was continued till the study was completed. At the end of study period (24 hours), the number of larvae consumed per fish for each fish species was determined. This study was carried out in the laboratory with 6 replicates. The experiment was repeated for Ae. albopictus. Overall, Oreochromis niloticus, Poecilia reticulata, Aplocheilus dayi and Puntius bimaculatus consumed 97.6, 66.9, 49.3 and 47.5 Ae. aegypti and 98.4, 62.3, 51.2 and 45.4 Ae. albopictus larvae respectively. All four fish species showed larvivorous activity and Oreochromis niloticus showed the highest larvivorous potential followed by Poecilia reticulata. Since Ae. aegypti and Ae. albopictus breed in water storage containers such as cement tanks, barrels and ornamental ponds, the fish species that showed high larvivorous potential may be considered for dengue vector larval control in such containers. In order to achieve good community participation for the use of larvivorous fish for dengue vector control, effective health education is of utmost importance.
Optimization of Critical Threshold Values for Aedes Mosquitoes based on Breteau Index in Kandy District of Sri Lanka.
(In: Proceedings of the International Postgraduate Research Conference 2017 (IPRC – 2017), Faculty of Graduate Studies, University of Kelaniya, Sri Lanka., 2017) Udayanga, N.W.B.A.L.; Gunathilaka, P.A.D.H.N.; Iqbal, M.C.M.; Kusumawathie, P.H.D.; Abeyewickreme, W.
Many countries, including Sri Lanka, mainly depend upon Stegomyia indices,such as Premise Index (PI), Breteau Index (BI),Container Index (CI), and Pupal Index (PI) for routine entomological surveillance of dengue. Among them, BI remain as the most widely used larval index for vector management prior to and during epidemic incidences. Properly defined threshold values for BI are of essence, to assist the prediction of dengue epidemics and as a leading indicator for vector control. However, Sri Lanka still lacks effective thresholds for BI to initiate and drive dengue vector management activities. Hence, the present study attempts to define threshold values for BI based on an empirical modelling approach for the Kandy District of Sri Lanka.
Potential Use of a Combined Sterile Insect Technique (SIT) and Wolbachia-Based Approach for the Control of the Dengue Vector Aedes albopictus in Sri Lanka
(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Wijegunawardana, N.D.A.D.; Chandrasena, T.G.A.N.; Abeyewickreme, W.; Dassanayake, R.S.; Xi, Z.; Bourtzis, K.; Gunawardene, Y. I. N.S.
This study addresses the possibility of using a novel and environmental friendly strategy of combined sterile insect technique (SIT) and a Wolbachia-based approach in Aedes albopictus population control efforts in Sri Lanka. The above strategy combines irradiation and the intracellular endosymbiont bacteria Wolbachia, in insects which are vertically transmitted from mother to offspring. Releasing sterile male mosquitoes in the wild will introduce sterility for suppression of Ae. albopictus wild mosquito population. The strategy aims at the releasing of sexually incompatible Wolbachia triple infected and irradiated male mosquitoes on a large scale to the natural environment. By integrating irradiation, any accidentally released female mosquito will be made fully sterile, and hence the risk of population replacement of the target population with triple infected mosquitoes is eliminated. Therefore, the combined SIT/IIT approach offers a safe and bio-secure strategy for the population suppression of Ae. albopictus in Sri Lanka. The overall work involved assessment of the density and species abundance of wild mosquito populations, introgression, and characterization of Wolbachia triple infected Ae. albopictus line in a Sri Lankan genetic background and determination of minimum sterility dose for the males and females of the introgressed line. Results revealed that Ae. albopictus mosquito was the dominant vector species in the study area (Narangodapaluwa PHI area) with an average ovitrap index of 75.25% (range; 56.9% - 94.7%) over the study year. The frequency of Wolbachia infection among the mosquito population was ~17% (13/78). The most prominent Wolbachia super group infecting the wild mosquito species was the B group and Ae. albopictus was naturally infected with both strains A and B. Eighty-five new alleles and 8 complete allelic profiles were submitted to the Wolbachia MLST database. All sequencing data were deposited in the Genebank under the accession numbers MH447376-MH470292 and MH756095-MH777430. Successful transfer of Wolbachia triple infection to Ae. albopictus into Sri Lankan genetic background was achieved through an introgression experiment and characterization of the newly developed Ae. albopictus line expressed partial CI and revealed competitive fitness cost for fecundity, fertility, and longevity compared with wild-type while there was no cost for pupation rate, adult emergence and sex ratio. Therefore, integration of an irradiation (dose; 30Gy) is recommended to achieve complete male and female sterility prior to mosquito release (minimum sterility dose for males - 28 Gy and females - 30 Gy). This minimum sterility dose is lower than the irradiation dose applied for SIT and had not resulted in a significant effect on male competitiveness. Therefore, a combined SIT and Wolbachia based approach in Ae. albopictus dengue vector control is recommended as an additional tool in integrated vector management in Sri Lanka.
Prediction of Dengue Incidence Based on Time Series Modelling in the District of Colombo, Sri Lanka
(International Postgraduate Research Conference 2019, Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2019) Udayanga, L.; Herath, K.; Gunanthilaka, N.; Iqbal, M.C.M.; Abeyewickreme, W.
Timely implementation of intervention activities, is essential in controlling dengue epidemics. This requires the prediction of dengue epidemics, while respecting the spatial and temporal trends in dengue incidence. However, such aspects are limitedly focused in dengue epidemic management of Sri Lanka. Therefore, the current study was conducted to develop a temporal prediction model for dengue incidence in the district of Colombo in Sri Lanka. Dengue cases reported from 2000 to 2018 in the district of Colombo were collected from the Epidemiology Unit, Sri Lanka. Selected meteorological parameters such as number of rainy days, monthly cumulative rainfall, minimum and maximum relative humidity and temperature corresponding to the same study period were collected from the Department of Meteorology, along with the Oceanic Niño Index (ONI) from the National Oceanic and Administration (NOAA) Centre. All the data were arranged at monthly level. After evaluation of the normality, seasonality, stationarity and seasonal stationarity of the epidemic data, a Seasonal Autoregressive Integrated Moving Average (SARIMA) model was fitted for the prediction of dengue by using the R statistical package. Subsequently, the meteorological factors and the dengue incidence was subjected to a cross correlation analysis to identify the most representative meteorological factors associated with dengue epidemic incidence and an Autoregressive Integrated Moving Average with Exogeneous Input (ARIMAX) model was fitted. The best fitted SARIMA (0, 1, 0) (3, 0, 0)12 model was characterized by an Akaike Information Criteria value (AIC) of -19.04, Bayesian information criterion (BIC) of -5.42, Mean error (ME) of 0.002 and Root Mean Square Error (RMSE) of 0.518. According to the cross correlation analysis, number of rainy days (RD) and Oceanic Niño Index (ONI) denoted a significant negative association with the reported dengue cases in Colombo, while monthly cumulative rainfall (RF), maximum relative humidity (Max_RH), maximum temperature (Max_T) and minimum temperature (Min_T) shared a positive correlation (P < 0.05 at 95% level of confidence). The best fitting ARIMAX model (as indicated below) was characterized by an AIC of -15.74, BIC of -11. 2, ME of 0.006 and RMSE of 0.171. ARIMA (0, 1, 1) + [-0.0006 RDt-3 + 0.0008 RFt-3 + 0.0260 Max_RHt-3 + 0.0766 Min_Tt—4 - 0.0661 ONIt-5] Based on the performance, the ARIMAX model is recommended to be used for the prediction of dengue incidence in the Colombo district to ensure rational allocation of resources for vector control and dengue epidemic management
A preliminary community survey of selected dengue patient households in the Ragama MOH, Gampaha District
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Wijegunawardana, N.D.A.D.; Gunathilaka, N.; Udayanga, L.; Gunawardene, N.; Dassanayake, R.; Chandrasena, N.; Bourtzis, K.K.; Abeyewickreme, W.
Socio-economic aspects of the local population has been found to directly influence the emergence of dengue epidemics. Thus, a preliminary community survey was conducted among 30 randomly selected dengue positive patient households in the Ragama Medical Officer of Health (MOH) area, in Gampaha District to assess the socio-economic and demographic level of the patients. Study premises were selected randomly based on the MOH records during the year of 2015 and the selection of the premises was purposely limited to Narangodapaluwa Public Health Inspector area that has reported the highest number of dengue cases. An interviewer administrated questionnaire was used for the collection of socio-economic and demographic aspects of the patient households. Among the selected households; 40% (n=12) had at least more than 2 dengue positive patients among the occupants, while 42 dengue positive patients were interviewed in total. Age distribution of positive patients ranged from 1 - 70 years, while mean and mode represented 35 and 19 years, respectively. Relative distribution of male to female ratio remained as 1:1. Around 50% of the patients had an educational level higher than intermediate school education (O/L). Based on the indirect questions regarding the possible factors affecting the DF transmissions, it was noted that only participants 26 out of 42 (61.90%), have been infected with DF more than once in their life time regardless of living in the same study area since birth. Twenty-two patients (52.38%) claimed that they believe, that the DF infection has acquired at home. Meanwhile others claimed (n=20, 47.68%) that possible DF infection acquired site could be outside environments, probably schools or the place of work. Cleanliness of the surroundings was maintained well at almost all households, while waste disposal was properly maintained at weekly intervals by urban council in 14 premises. Others practiced open ground burning twice a week. Most of the respondents were willing to support Aedes control measures and follow mosquito bite prevention methods (n=28, 93.33%). Majority of the households (n=21) were not satisfied with the government vector controlling activates within the area. There is no significant association between socio demographic and economic data with DF transmission within the study population. Relative abundance of Aedes mosquito population in existing rubber plantation could be a reason for the occurrence of high rate of DF cases. Thus, practice of effective integrated vector control measures within the study area is highly recommended for the controlling of dengue.
Prevalence of dengue vector breeding habitats among selected Schools in Gampaha District of Sri Lanka
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2016) Radhika, N.M.L.; Gunathilaka, P.A.D.H.N.; Kasturiratne, K.T.A.A.; Abeyewickreme, W.
Aedes aegypti and Aedes albopictus are the vectors responsible for the transmission of dengue viruses in Sri Lanka. Gampaha District has been ranked as the second most Dengue affected area. Recently, health authorities have identified that over 54 percent of schools have dengue mosquito breeding sites. However, the entomological information on the dengue vectors in School premises are not available. Therefore, the present study was carried out to identify the different breeding sites of dengue vector mosquitoes within school premises of randomly selected schools in Gampaha District of Sri Lanka. The premises of the selected schools (n= 34) were surveyed from May to October in 2016 for the availability of potential breeding habitats and the presence of vector breeding through entomological surveys. Collected vectors were identified morphologically and categorized inn to species level. All data on breeding habitats and number of vectors identified were recorded. According to survey, out of 34 schools surveyed; infested water-holding containers by Ae. albopictus were observed at 16 schools (47, 05%). Tree holes (Bridelia retusa tree), leaf axils of banana tree and fallen leaves were observed as natural breeding sites while, discarded plastic food containers plastic paint containers, broken pet bottles, tire marks on the ground, water retaining flower pots and plastic barrels were observed as artificial breeding sites. Breeding of Ae. aegypti was not identified among the school premises surveyed. Improper management of solid waste has affected positively in creating suitable habitats for vector breeding. Therefore, continuous monitoring of dengue vector breeding habitats and school based vector controlling interventions should be implemented through proper awareness and active participation for eliminating breeding habitats.
Role of Larval Indices on the Incidence of Dengue Epidemics in Akurana, Medical Officer of Health (MOH) Area, Kandy.
(In: Proceedings of the International Postgraduate Research Conference 2017 (IPRC – 2017), Faculty of Graduate Studies, University of Kelaniya, Sri Lanka., 2017) Udayanga, N.W.B.A.L.; Gunathilaka, P.A.D.H.N.; Iqbal, M.C.M.; Fernando, M.A.S.T.; Abeyewickreme, W.
As in many other Asian countries, vector control entities in Sri Lanka also depend upon larval indices as the major driving factor of routine entomological surveillance and management of dengue vectors. However, studies aimed at defining the role of larval indices, which reflect the population dynamics of dengue vectors, on the incidence of dengue outbreaks are limited. This is mainly due to restrictions in long-term vector density related data. Hence, the current study attempts to evaluate the role of larval indices on the incidence of dengue epidemics in Akurana, Medical Officer of Health (MOH) area.
A Statistical Approach to Define Thresholds for Dengue Epidemic Management in Akurana Medical Officer of Health Area, Kandy District of Sri Lanka
(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Udayanga, N.W.B.A.L.; Gunathilaka, P.A.D.H.N.; Iqbal, M.C.M.; Fernando, M.A.S.T.; Abeyewickreme, W.
Stegomyia indices, namely; Premise Index (PI), Breteau Index (BI) and Container Index (CI) are used forvector management approaches in Sri Lanka. Properly defined threshold values for larval indices are of higher importance to provide forecasts on dengue epidemics and also for effective larval management of dengue vectors. However, such critical thresholds are poorly defined for Sri Lanka. The present study aimed to define threshold values forabove larval indices for dengue epidemic management in the Akurana Medical Officer of Health (MOH) in the Kandy District. Larval surveys were conducted on a monthly basis from January, 2016 to June, 2018. Four larval indices, namely BI for Aedesaegypti (BIA) and Aedesalbopictus (BIB), PI and CI were calculated. Further, monthly larval indices of AkuranaMOH area from January, 2012 to December, 2015, were obtained from the MOH office, along with monthly reported dengue cases for the entire study period. Receiver Operating Characteristic (ROC) curves in SPSS (version 23) were used to assess the discriminative power of the larval indices in determiningdengue epidemics and thresholds based on larval indices. As indicated by the area of ROC curve (AUC), the BIA (0.661) and PI (0.637) were having a notable discriminative power to forecast dengue epidemics at a two-month lag period. Both BIB (0.397) and CI (0.526) were non-informative influencers at one and two-month lag periods. The BIA and PI were better predictors of dengue incidence than BIB and CI. Based on the ROC curve, three risk thresholds were defined for BIA as Low Risk (BIA≤2.1), Moderate Risk (3.9≤BIA<4.85), and High Risk (BIA≥4.85), with respect to Ae. aegypti. According to the PI, thresholds were defined as Low Risk (PI≤6.2), Moderate Risk (7.7≤ PI<9.9), and High Risk (PI≥ 9.9). Threshold values defined for BI of Ae. aegypti and PI, could be recommended to be considered in implementing vector control efforts in the above study area for effective dengue epidemic management, through pre planned entomological management of dengue vectors.
Sterile Insect Technique for Controlling Aedes albopictus (Skuse); Sex Separation and Mating Competitiveness
(19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Harishchandra, J.; Hapugoda, M.; Premaratne, R.G.; Abeyewickreme, W.
Sterile Insect Technique (SIT) introduced by Edward F. Knipling in 1950s has been shown as an effective and sustainable genetic approach to control populations of selected pest insects in area wide integrated pest management programmes. Successfulness of this approach depends on the availability of an efficient sexing method and production of sterile males competitive enough to compete with wild males. In the context of developing SIT for the control of dengue vector Aedes albopictus (Skuse) in Sri Lanka, a method for separation of male pupae was tested and mating competitiveness of irradiated males against wild males was evaluated under laboratory conditions. Male pupae of the F42 generation of Ae. albopictus (Gampaha strain) were separated from female pupae using mechanical sieving method. A set of three stainless steel sieves of mesh sizes 1.4, 1.25 and 1.12mm were placed one on the other in descending order of size towards the bottom, forming a column immersed in a water jar. All pupae were poured on to the top sieve and shaken gently for seven minutes. Pupae were collected from each sieve and the male and female counts were taken after emergence of adults. Male and female pupae used for the competitiveness assessment were separated by the above sieving method. Male pupae (F42, age 28-40hours) were exposed to Gamma radiation (Gamma 220, Atomic Energy of Canada Ltd., Co60) at a dose of 50Gy by placing 300 male pupae in each plastic vial with 10ml of water. Dosimetry was performed using Frickey method. Wild fertile males and females reared from field-collected eggs from Gampaha (F1) were used to compete and cross with irradiated males respectively in different ratios. Two days after the emergence, the adult mosquitoes were caged (Bug Dorm 30X30X30cm) with ratios of irradiated males: wild males: wild virgin females 1:1:1, 3:1:1 and 5:1:1 (females, n = 100). Fertile control was set with wild males and wild virgin females 1:1. and an irradiated control was set with irradiated males with wild virgin females 1:1. Mosquitoes were allowed to mate for 3 days with access to 10% sugar solution. Then the mosquitoes were fed with cattle blood and engorged females were isolated in oviposition tubes. After 4 days, females were returned into cages and the filter papers containing eggs were allowed to dry. Eggs were hatched after one week and the hatching rates were compared. From the pupae retained in the sieve of mesh size 1.12mm, 98.3% were males. The mean hatch rates of fertile and irradiated controls and with ratios of irradiated males: wild fertile males: wild virgin females 1:1:1, 3:1:1, 5:1:1 were 80.24%±1.63SEM, 2.42%±0.57SEM, 56.74%±5.79SEM, 37.33%±4.76SEM and 34.23%±4.73SEM respectively. Fried Competitive Index (C) of irradiated males compared to controls was 0.43. Results show sieving method can be used for separating male pupae for irradiation with 98% accuracy. Irradiated males were less than 50% competitive as wild males under laboratory conditions