IRSPAS 2018
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Item Predicting dengue incidences using rainfall and temperature(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Pushpakanthi, U. B. N.; Perera, S. S. N.Dengue fever is a serious illness caused by a virus, which is transmitted through the infected female mosquito, namely Aedes aegypti (principal vector) and Aedes albopictus, through bites or blood meals on human hosts. Dengue is a major public health problem in most countries in tropical regions and it has spread rapidly in many parts of the world including Sri Lanka. The urban population in Sri Lanka is highly vulnerable while Colombo District is at high risk. This study focuses on the dengue cases reported around Colombo Municipal Council (CMC) in Sri Lanka. The aims of this study are to identify the lags for explanatory variables which are affected the dengue incidence most, and to identify a distribution of weekly dengue cases. The explanatory variables are average rainfall per week, average of the maximum temperature per week and average of the minimum temperature per week. Weekly dengue incidents from January 2009 to October 2017 in CMC were considered. By applying the cross correlation analysis, it showed that the average of the maximum temperature per week and the average rainfall per week have a significant influence to occurrence of dengue cases after 10 weeks their occurrences. Therefore, the best-lags were ten weeks for both weekly average maximum temperature and weekly average rainfall and, best-lag for weekly average minimum temperature was zero. The Negative Binomial regression model was used in this study. The number of dengue cases per week in CMC area followed negative binomial distribution given that the average rainfall and average maximum temperature before 10 weeks. This predictive distribution can be used as an early warning signal so that public health officials can be prepared in advance to minimize the disease burden.Item Abundance and distribution pattern of Aedes aegypti and Aedes albopictus in selected urban, sub-urban and rural areas of Gampaha District, Sri Lanka(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Dalpadado, C. P. R. D.; Amarasinghe, L. D.The abundance and distribution of Aedes aegypti and Aedes albopictus, vectors of dengue fever, were determined at six localities in Gampaha District, which is the district with the occurrence of second highest number of dengue cases during last five years. Negombo and Wattala areas were selected to represent urbanized communities, Gampaha and Attanagalla to represent sub-urban communities and Dompe and Divulapitiya were selected for the rural communities based on population density. Percentage of premises infected with Aedes larvae (Premise Index) and the number of positive containers for 100 premises inspected (Breteau Index) were used as a proxy to determine the abundance of vectors. Larval collections were done monthly during April 2016 to June 2018 using random sampling technique for minimum 100 houses within a radius of 300 m. Potential breeding places in each site were identified and categorized accordingly. Out of 7916 premises examined, 1011 (12.8%) premises were found to be positive for Aedes mosquitoes. Among them 10.1% and 89.9% were found to be positive for Ae . aegypti and Ae . albopictus, respectively . Ae . aegypti was mostly prevalent in highly urbanized MOH areas (73%) while it showed low abundance in sub urban (21%) and rural (6%) areas. On contrary, abundance of Ae . albopictus was highest in sub-urban areas (47%) and lowest in urban areas (18%). Premise index (PI) for Ae . aegypti in urbanized areas were significantly higher than that of sub-urban (F=9.13, p<0.05) and rural areas (F=15.49, p<0.05) in Gampaha District and there was no significant difference (F=4.04, p>0.05) between PI of Ae . aegypti in sub urban and rural areas. The PI of Ae . albopictus in sub-urban areas was significantly higher than that of urban areas (F=15.43, p<0.05). There was no significant difference (F=1.44, p>0.05) between PI of Ae . albopictus in sub-urban and rural areas. Similarly, there was no significant difference between mix indices for Ae . aegypti and Ae . albopictus in Gampaha district (p>0.05). There was a strong correlation between the Breteau Index and the number of dengue patients reported in urbanized areas (r<0.5). Higher correlation was recorded with Ae . aegypti than Ae . albopictus. Therefore, occurrence of dengue epidemics are strongly correlated with Ae .aegypti indices in city areas of Gampaha District and present study suggests that Stegomyia indices can be used as a proxy to determine dengue transmission risk.Item Indoor resting preference of Aedes (Stegomia; Culicidae) mosquitoes in urban human dwellings of Gampaha District, Sri Lanka(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Dalpadado, C. P. R. D.; Amarasinghe, L. D.The current study was designed to identify the preferred resting height, place and surface of Dengue vectors, Aedes aegypti and Aedes albopictus, near human dwellings located in urban cites in Gampaha District, Sri Lanka during August 2017 to February 2018. Adult mosquitoes were collected systematically using manual aspiration technique, during 6:00 a.m. and 9.00 a.m. and 4:00 p.m. and 7:00 p.m. from all the resting localities from 280 premises. At each station, resting place, nature of the resting surface and resting height were recorded and mosquitoes were identified down to species level. In total, 378 Aedes mosquitoes (Aedes aegypti 82.3%, Aedes albopictus 17.7%) were collected and of the collected Aedes mosquitoes, 1:8 male to female ratio was observed. 68.3% of Aedes mosquitoes preferred to rest closer to the ground level and 24.9% mosquitoes rested between 1 m to 2 m above the ground level. 4.8% Aedes mosquitoes were found resting between 2 m to 3 m of height and only 1.5% Ae . aegypti mosquitoes were found resting 3 m above the ground level and none of the Ae . albopictus was recorded above 3 m from the ground level. There was no significant difference (p=0.001<0.05) between males and females in resting height for both vectors. Bedrooms were more frequently visited by resting Ae. aegypti mosquitoes (51.8%), followed by living rooms (28.5%) and kitchen (12.4%) while 52.4% female Ae . albopictus were found resting on living rooms and 28.6% in bed rooms. Identified indoor resting places were significantly different for Ae . aegypti and Ae . albopictus in Gampaha district (χ2= 20.895, P< 0.05). Majority of Aedes female mosquitoes were found resting on cloth hangings and curtains (49.3% Ae . aegypti, 77.8% Ae . albopictus) followed by under furniture (24.3% Ae . aegypti, 22.2% Ae . albopictus) . The mean number of mosquitoes per positive premise was 1.35 and maximum total number of Aedes mosquitoes collected at a premise was 7. The maximum number of females collected was 6 and maximum for males were 2 per premise. Higher abundance of Ae . aegypti in the region increases the transmission risk greatly, since Ae . aegypti bites more than one host to complete one blood meal. Since females were found resting closer to floor level especially in hidden locations such as cloth hangings, curtains and under furniture, indoor space spraying should be strengthened targeting these locations to control dengue in future.