Larval Indices of Vector Mosquitoes as Predictors of Dengue Epidemics: An Approach to Manage Dengue Outbreaks Based on Entomological Parameters in the Districts of Colombo and Kandy, Sri Lanka.

BACKGROUND: Early detection of dengue epidemics is a vital aspect in control programmes. Predictions based on larval indices of disease vectors are widely used in dengue control, with defined threshold values. However, there is no set threshold in Sri Lanka at the national or regional levels for Aedes larval indices. Therefore, the current study aimed at developing threshold values for vector indices in two dengue high-risk districts in Sri Lanka. METHODS: Monthly vector indices (House Index [HI], Container Index [CI], Breteau Index for Aedes aegypti [BIagp], and Ae. albopictus [BIalb]), of ten selected dengue high-risk Medical Officer of Health (MOH) areas located in Colombo and Kandy districts, were collected from January 2010 to June 2019, along with monthly reported dengue cases. Receiver Operating Characteristic (ROC) curve analysis in SPSS (version 23) was used to assess the discriminative power of the larval indices in identifying dengue epidemics and to develop thresholds for the dengue epidemic management. RESULTS: Only HI and BIagp denoted significant associations with dengue epidemics at lag periods of one and two months. Based on Ae. aegypti, average threshold values were defined for Colombo as Low Risk (2.4 ≤ BIagp < 3.8), Moderate Risk (3.8 ≤ BIagp < 5), High Risk (BIagp ≥ 5), along with BIagp 2.9 ≤ BIagp < 4.2 (Low Risk), 4.2 ≤ BIagp < 5.3 (Moderate Risk), and BIagp ≥ 5.3 (High Risk) for Kandy. Further, 5.5 ≤ HI < 8.9, 8.9 ≤ HI < 11.9, and HI ≥ 11.9 were defined as Low Risk, Moderate Risk, and High Risk average thresholds for HI in Colombo, while 6.9 ≤ HI < 9.1 (Low Risk), 8.9 ≥ HI < 11.8 (Moderate Risk), and HI ≥ 11.8 (High Risk) were defined for Kandy. CONCLUSIONS: The defined threshold values for Ae. aegypti and HI could be recommended as indicators for early detection of dengue epidemics and to drive vector management activities, with the objective of managing dengue epidemics with optimal usage of financial, technical, and human resources in Sri Lanka.

Climate change induced vulnerability and adaption for dengue incidence in Colombo and Kandy districts: the detailed investigation in Sri Lanka.

BACKGROUND: Assessing the vulnerability of an infectious disease such as dengue among endemic population is an important requirement to design proactive programmes in order to improve resilience capacity of vulnerable communities. The current study aimed to evaluate the climate change induced socio-economic vulnerability of local communities to dengue in Colombo and Kandy districts of Sri Lanka. METHODS: A total of 42 variables (entomological, epidemiological, meteorological parameters, land-use practices and socio-demographic data) of all the 38 Medical Officer of Health (MOH) areas in the districts of Colombo and Kandy were considered as candidate variables for a composite index based vulnerability assessment. The Principal Component Analysis (PCA) was used in selecting and setting the weight for each indicator. Exposure, Sensitivity, Adaptive Capacity and Vulnerability of all MOH areas for dengue were calculated using the composite index approach recommended by the Intergovernmental Panel on Climate Change. RESULTS: Out of 42 candidate variables, only 23 parameters (Exposure Index: six variables; Sensitivity Index: 11 variables; Adaptive Capacity Index: six variables) were selected as indicators to assess climate change vulnerability to dengue. Colombo Municipal Council (CMC) MOH area denoted the highest values for exposure (0.89: exceptionally high exposure), sensitivity (0.86: exceptionally high sensitivity) in Colombo, while Kandy Municipal Council (KMC) area reported the highest exposure (0.79: high exposure) and sensitivity (0.77: high sensitivity) in Kandy. Piliyandala MOH area denoted the highest level of adaptive capacity (0.66) in Colombo followed by Menikhinna (0.68) in Kandy. The highest vulnerability (0.45: moderate vulnerability) to dengue was indicated from CMC and the lowest indicated from Galaha MOH (0.15; very low vulnerability) in Kandy. Interestingly the KMC MOH area had a notable vulnerability of 0.41 (moderate vulnerability), which was the highest within Kandy. CONCLUSIONS: In general, vulnerability for dengue was relatively higher within the MOH areas of Colombo, than in Kandy, suggesting a higher degree of potential susceptibility to dengue within and among local communities of Colombo. Vector Controlling Entities are recommended to consider the spatial variations in vulnerability of local communities to dengue for decision making, especially in allocation of limited financial, human and mechanical resources for dengue epidemic management.

Predatory efficacy of five locally available copepods on Aedes larvae under laboratory settings: An approach towards bio-control of dengue in Sri Lanka.

Many countries are in search of more effective and sustainable methods for controlling dengue vectors, due to undeniable inefficiencies in chemical and mechanical vector control methods. Bio-control of vectors by copepods is an ideal method of using interactions in the natural ecosystem for vector management, with minimum consequences on the environment. Current study determined the predatory efficacy of five locally abundant copepod species on, Aedes larvae under laboratory conditions. Copepods were collected from the pre-identified locations within the districts of Gampaha and Kandy, and identified morphologically. Individual species of copepods were maintained as separate colonies with Paramecium culture and wheat grain as supplementary food. Five adult copepods of each species was introduced into separate containers with 200 larvae (1st instar) of Aedes aegypti. Number of larvae survived in containers were enumerated at 3 hour intervals within a duration of 24 hours. Each experiment was repeated five times. The same procedure was followed for Ae. albopictus. Significance in the variations among predation rates was evaluated with General Linear Modelling (GLM) followed by Tukey's pair-wise comparison in SPSS (version 23). Significant variations in predation rates of studied copepod species were reported (p<0.05), whereby M. leuckarti indicated the highest followed by M. scrassus, while C. languides indicated the lowest predatory efficacy. The effect of different Aedes larval species on the predation rates of copepods remained significant (p<0.05), even though the effect on predatory efficiency was not significant. Based on the findings, both M. leuckarti and M. scrassus, with the highest predatory efficiencies, could be recommended as potential candidates for biological controlling of Aedes vectors in Sri Lanka.

Mechanistic understanding of crystal violet dye sorption by woody biochar: implications for wastewater treatment.

Dye-based industries, particularly small and medium scale, discharge their effluents into waterways without treatment due to cost considerations. We investigated the use of biochars produced from the woody tree Gliricidia sepium at 300 °C (GBC300) and 500 °C (GBC500) in the laboratory and at 700 °C from a dendro bioenergy industry (GBC700), to evaluate their potential for sorption of crystal violet (CV) dye. Experiments were conducted to assess the effect of pH reaction time and CV loading on the adsorption process. The equilibrium adsorption capacity was higher with GBC700 (7.9 mg g-1) than GBC500 (4.9 mg g-1) and GBC300 (4.4 mg g-1), at pH 8. The CV sorption process was dependent on the pH, surface area and pore volume of biochar (GBC). Both Freundlich and Hill isotherm models fitted best to the equilibrium isotherm data suggesting cooperative interactions via physisorption and chemisorption mechanisms for CV sorption. The highest Hill sorption capacity of 125.5 mg g-1 was given by GBC700 at pH 8. Kinetic data followed the pseudo-second-order model, suggesting that the sorption process is more inclined toward the chemisorption mechanism. Pore diffusion, π-π electron donor-acceptor interaction and H-bonding were postulated to be involved in physisorption, whereas electrostatic interactions of protonated amine group of CV and negatively charged GBC surface led to a chemisorption type of adsorption. Overall, GBC produced as a by-product of the dendro industry could be a promising remedy for CV removal from an aqueous environment.

Use of cyclopoid copepods for control of Anopheles (Diptera: Culicidae) mosquito larvae to prevent re-emergence of malaria in Sri Lanka.

BACKGROUND & OBJECTIVES: Although malaria is eliminated from Sri Lanka, there is a possible risk of spread from infected persons coming from malaria endemic countries. The presence of major and potential vectors in several parts of the country along with drug resistance, necessitates the identification of effective and novel control methods. The present study focused on identifying effective biological control agents for anopheline larvae using carnivorous copepods under laboratory and field conditions to prevent re-introduction of malaria in the country. METHODS: Three copepod species, namely Mesocyclops scrassus, Cyclops varicans and C. languides collected from different areas in the country were cultured by adding supplementary food, and their predatory efficacy was evaluated under laboratory and field conditions. RESULTS: Significant variation (p <0.05) was observed in predation rates of studied copepod species. The species M. scrassus showed the highest predacious efficiency, and consumed the highest number of anopheline larvae under laboratory and field conditions. Further, M. scrassus had higher survival rate than C. varicans and C. languides. INTERPRETATION & CONCLUSION: The results of the study suggest that the predatory copepod M. scrassus can be used as a bio-control agent for the control of Anopheles mosquitoes to prevent re-emergence of malaria in the country. Additional research is suggested to identify naturally available copepod species and their predatory efficacy.

Using multiple methods to assess heavy metal pollution in an urban city.

Heavy metal pollution in urban cities is now an accepted fact. An understanding of the natural and anthropogenic contributions to heavy metal accumulation in these cities is necessary to develop strategies to mitigate their impacts, particularly on human health. Here, we used multiple records using geological and biological pollution indicators to assess the extent of pollution in the Colombo Metropolitan Region (CMR), Sri Lanka. Elemental concentrations of Cu, Zn, Ni and Pb were determined in four depositories: surface soil (90 samples), canal sediments and canal water (45 samples each) and vegetation (62 samples). These were mapped using GIS overlapping the road network to identify hotspots of heavy metals. While the surface soil, canal sediments and leaves of trees had higher and different amounts than background levels of heavy metals, canal water had low levels. Our results suggest that anthropogenic activities are the major source of heavy metals in an urban city, and unique natural factors, such as coastal conditions, terrain morphology and climate, combine and influence the distribution of these metals. We discuss the possible remediation of metal pollution and the necessity of a holistic multi-proxy approach to understand urban heavy metal contamination in a rapidly populating area.

Socio-economic, Knowledge Attitude Practices (KAP), household related and demographic based appearance of non-dengue infected individuals in high dengue risk areas of Kandy District, Sri Lanka.

BACKGROUND: Socio-economic, demographic factors and Knowledge Attitude Practices (KAPs) have been recognized as critical factors that influence the incidence and transmission of dengue epidemics. However, studies that characterize above features of a risk free or low risk population are rare. Therefore, the present study was conducted to characterize the household related, demographic, socio-economic factors and KAPs status of five selected dengue free communities. METHOD: An analytical cross-sectional survey was conducted on selected demographic, socio-economic, household related and KAPs in five selected dengue free communities living in dengue risk areas within Kandy District, Central Province, Sri Lanka. Household heads of 1000 randomly selected houses were interviewed in this study. Chi-square test for independence, cluster analysis and Principal Coordinates (PCO) analysis were used for data analysis. RESULTS: Knowledge and awareness regarding dengue, (prevention of the vector breeding, bites of mosquitoes, disease symptoms and waste management) and attitudes of the community (towards home gardening, composting, waste management and maintenance of a clean and dengue free environment) are associated with the dengue free status of the study populations. CONCLUSIONS: The vector controlling authorities should focus on socio-economic, demographic and KAPs in stimulating the community to cooperate in the integrated vector management strategies to improve vector control and reduce transmission of dengue within Kandy District.

Ultramafic geoecology of South and Southeast Asia.

Globally, ultramafic outcrops are renowned for hosting floras with high levels of endemism, including plants with specialised adaptations such as nickel or manganese hyperaccumulation. Soils derived from ultramafic regoliths are generally nutrient-deficient, have major cation imbalances, and have concomitant high concentrations of potentially phytotoxic trace elements, especially nickel. The South and Southeast Asian region has the largest surface occurrences of ultramafic regoliths in the world, but the geoecology of these outcrops is still poorly studied despite severe conservation threats. Due to the paucity of systematic plant collections in many areas and the lack of georeferenced herbarium records and databased information, it is not possible to determine the distribution of species, levels of endemism, and the species most threatened. However, site-specific studies provide insights to the ultramafic geoecology of several locations in South and Southeast Asia. The geoecology of tropical ultramafic regions differs substantially from those in temperate regions in that the vegetation at lower elevations is generally tall forest with relatively low levels of endemism. On ultramafic mountaintops, where the combined forces of edaphic and climatic factors intersect, obligate ultramafic species and hyperendemics often occur. Forest clearing, agricultural development, mining, and climate change-related stressors have contributed to rapid and unprecedented loss of ultramafic-associated habitats in the region. The geoecology of the large ultramafic outcrops of Indonesia's Sulawesi, Obi and Halmahera, and many other smaller outcrops in South and Southeast Asia, remains largely unexplored, and should be prioritised for study and conservation.

Cells of the connective tissue differentiate and migrate into pollen sacs.

In angiosperms, archesporial cells in the anther primordium undergo meiosis to form haploid pollen, the sole occupants of anther sacs. Anther sacs are held together by a matrix of parenchyma cells, the connective tissue. Cells of the connective tissue are not known to differentiate. We report the differentiation of parenchyma cells in the connective tissue of two Gordonia species into pollen-like structures (described as pseudopollen), which migrate into the anther sacs before dehiscence. Pollen and pseudopollen were distinguishable by morphology and staining. Pollen were tricolpate to spherical while pseudopollen were less rigid and transparent with a ribbed surface. Both types were different in size, shape, staining and surface architecture. The ratio of the number of pseudopollen to pollen was 1:3. During ontogeny in the connective tissue, neither cell division nor tetrad formation was observed and hence pseudopollen were presumed to be diploid. Only normal pollen germinated on a germination medium. Fixed preparations in time seemed to indicate that pseudopollen migrate from the connective tissue into the anther sac.