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      Predicting Local Dengue Transmission in Guangzhou, China, through the Influence of Imported Cases, Mosquito Density and Climate Variability

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          Abstract

          Introduction

          Each year there are approximately 390 million dengue infections worldwide. Weather variables have a significant impact on the transmission of Dengue Fever (DF), a mosquito borne viral disease. DF in mainland China is characterized as an imported disease. Hence it is necessary to explore the roles of imported cases, mosquito density and climate variability in dengue transmission in China. The study was to identify the relationship between dengue occurrence and possible risk factors and to develop a predicting model for dengue’s control and prevention purpose.

          Methodology and Principal Findings

          Three traditional suburbs and one district with an international airport in Guangzhou city were selected as the study areas. Autocorrelation and cross-correlation analysis were used to perform univariate analysis to identify possible risk factors, with relevant lagged effects, associated with local dengue cases. Principal component analysis (PCA) was applied to extract principal components and PCA score was used to represent the original variables to reduce multi-collinearity. Combining the univariate analysis and prior knowledge, time-series Poisson regression analysis was conducted to quantify the relationship between weather variables, Breteau Index, imported DF cases and the local dengue transmission in Guangzhou, China. The goodness-of-fit of the constructed model was determined by pseudo- R 2 , Akaike information criterion (AIC) and residual test. There were a total of 707 notified local DF cases from March 2006 to December 2012, with a seasonal distribution from August to November. There were a total of 65 notified imported DF cases from 20 countries, with forty-six cases (70.8%) imported from Southeast Asia. The model showed that local DF cases were positively associated with mosquito density, imported cases, temperature, precipitation, vapour pressure and minimum relative humidity, whilst being negatively associated with air pressure, with different time lags.

          Conclusions

          Imported DF cases and mosquito density play a critical role in local DF transmission, together with weather variables. The establishment of an early warning system, using existing surveillance datasets will help to control and prevent dengue in Guangzhou, China.

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          Most cited references39

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          Potential effect of population and climate changes on global distribution of dengue fever: an empirical model.

          Existing theoretical models of the potential effects of climate change on vector-borne diseases do not account for social factors such as population increase, or interactions between climate variables. Our aim was to investigate the potential effects of global climate change on human health, and in particular, on the transmission of vector-borne diseases. We modelled the reported global distribution of dengue fever on the basis of vapour pressure, which is a measure of humidity. We assessed changes in the geographical limits of dengue fever transmission, and in the number of people at risk of dengue by incorporating future climate change and human population projections into our model. We showed that the current geographical limits of dengue fever transmission can be modelled with 89% accuracy on the basis of long-term average vapour pressure. In 1990, almost 30% of the world population, 1.5 billion people, lived in regions where the estimated risk of dengue transmission was greater than 50%. With population and climate change projections for 2085, we estimate that about 5-6 billion people (50-60% of the projected global population) would be at risk of dengue transmission, compared with 3.5 billion people, or 35% of the population, if climate change did not happen. We conclude that climate change is likely to increase the area of land with a climate suitable for dengue fever transmission, and that if no other contributing factors were to change, a large proportion of the human population would then be put at risk.
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            A simulation model of the epidemiology of urban dengue fever: literature analysis, model development, preliminary validation, and samples of simulation results.

            We have developed a pair of stochastic simulation models that describe the daily dynamics of dengue virus transmission in the urban environment. Our goal has been to construct comprehensive models that take into account the majority of factors known to influence dengue epidemiology. The models have an orientation toward site-specific data and are designed to be used by operational programs as well as researchers. The first model, the container-inhabiting mosquito simulation model (CIMSiM), a weather-driven dynamic life-table model of container-inhabiting mosquitoes such as Aedes aegypti, provides inputs to the tranmission model, the dengue simulation model (DENSiM); a description and validation of the entomology model was published previously. The basis of the transmission model is the simulation of a human population growing in response to country- and age-specific birth and death rates. An accounting of individual serologies is maintained by type of dengue virus, reflecting infection and birth to seropositive mothers. Daily estimates of adult mosquito survival, gonotrophic development, and the weight and number of emerging females from the CIMSiM are used to create the biting mosquito population in the DENSiM. The survival and emergence values determine the size of the population while the rate of gonotrophic development and female weight estimates influence biting frequency. Temperature and titer of virus in the human influences the extrinsic incubation period; titer may also influence the probability of transfer of virus from human to mosquito. The infection model within the DENSiM accounts for the development of virus within individuals and its passage between both populations. As in the case of the CIMSiM, the specific values used for any particular phenomenon are on menus where they can be readily changed. It is possible to simulate concurrent epidemics involving different serotypes. To provide a modicum of validation and to demonstrate the parameterization process for a specific location, we compare simulation results with reports on the nature of epidemics and seroprevalence of antibody in Honduras in low-lying coastal urbanizations and Tegucigalpa following the initial introduction of dengue-1 in 1978 into Central America. We conclude with some additional examples of simulation results to give an indication of the types of questions that can be investigated with the models.
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              Effect of temperature on the vector efficiency of Aedes aegypti for dengue 2 virus.

              The effect of temperature on the ability of Aedes aegypti to transmit dengue (DEN) 2 virus to rhesus monkeys was assessed as a possible explanation for the seasonal variation in the incidence of dengue hemorrhagic fever in Bangkok, Thailand. In two laboratory experiments, a Bangkok strain of Ae. aegypti was allowed to feed upon viremic monkeys infected with DEN-2 virus. Blood-engorged mosquitoes were separated into two groups and retained at constant temperatures. Virus infection and transmission rates were determined for Ae. aegypti at intervals ranging from 4 to 7 days during a 25-day incubation period. Results of the first experiment for mosquitoes infected with a low dose of DEN-2 virus and maintained at 20, 24, 26, and 30 degrees C, indicated that the infection rate ranged from 25% to 75% depending on the incubation period. However, DEN-2 virus was transmitted to monkeys only by Ae. aegypti retained at 30 degrees C for 25 days. In the second experiment, the infection rate for Ae. aegypti that ingested a higher viral dose, and incubated at 26, 30, 32, and 35 degrees C ranged from 67% to 95%. DEN-2 virus was transmitted to monkeys only by mosquitoes maintained at greater than or equal to 30 degrees C. The extrinsic incubation period was 12 days for mosquitoes at 30 degrees C, and was reduced to 7 days for mosquitoes incubated at 32 degrees C and 35 degrees C. These results imply that temperature-induced variations in the vector efficiency of Ae. aegypti may be a significant determinant in the annual cyclic pattern of dengue hemorrhagic fever epidemics in Bangkok.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2014
                14 July 2014
                : 9
                : 7
                : e102755
                Affiliations
                [1 ]State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Changping, Beijing, China
                [2 ]Key Laboratory of Surveillance and Early-Warning on Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing, China
                [3 ]School of Population Health, University of Adelaide, Adelaide, South Australia, Australia
                [4 ]Department of Preventive Medicine, College of Basic Medical Sciences, Shandong University of Traditional Chinese Medicine, Jinan, Shandong, China
                [5 ]Xiamen Entry-Exit Inspection and Quarantine Bureau, Xiamen, China
                [6 ]WHO Collaborating Centre for Vector Surveillance and Management, Changping, Beijing, China
                [7 ]Centre for Environment and Population Health, Nathan Campus, Griffith University, Nathan, Queensland, Australia
                [8 ]Shandong University Climate Change and Health Center, Jinan, China
                [9 ]Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Hangzhou, China
                Duke-National University of Singapore Graduate Medical School, Singapore
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: SWS QYL. Analyzed the data: SWS WWY HLZ CGW XBL BC WZY. Wrote the paper: SWS WWY PB HLZ CGW XBL BC WZY QYL.

                Article
                PONE-D-14-03943
                10.1371/journal.pone.0102755
                4097061
                25019967
                62a12cbb-858c-46dc-9244-bf2fc50ab692
                Copyright @ 2014

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 26 January 2014
                : 23 June 2014
                Page count
                Pages: 10
                Funding
                The study was supported by the National Basic Research Program of China (973 Program) (Grant No. 2012CB955504); The National Natural Science Foundation of China (NSFC) (Grant No. 81273139); The Special Research Program for Health (Grant No. 201202006). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Medicine and Health Sciences
                Epidemiology
                Infectious Disease Epidemiology
                Infectious Diseases
                Viral Diseases
                Dengue Fever
                Tropical Diseases
                Neglected Tropical Diseases

                Uncategorized
                Uncategorized

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