Environmental factors and incidence of dengue fever and dengue haemorrhagic fever in an urban area, Southern Thailand

Using the enumeration district (ED) block level this study looked at the incidence of dengue fever and dengue haemorrhagic fever (DF/DHF) within the Songkhla municipality in Thailand. Each of the 146 blocks in this area were considered as study units and surveyed for their environmental characteristics. A total of 287 cases of DH/DHF occurring in the year 1998 were selected for this study and the location of their homes mapped. Clustering analysis showed point clustering of the homes (P<0.0001) which was probably due to high density habitation, without any actual prevalence of case clustering. There was no evidence of clustering of the ED blocks with an incidence of DF/DHF (P=0.32). DF/DHF incidence for each block was strongly associated with the percentages of shop-houses, brick-made houses and houses with poor garbage disposal (all P<0.01). DF/DHF control should be emphasized for the areas which have a predominance of these housing types.     

Association between dengue incidence and climatic factors

OBJECTIVE: To describe the occurrence of autochthonous dengue cases according to sex, age, suspected infection site and its relation with climatic variables. METHODS: Autochthonous dengue cases reported in S?o Sebasti?o, Southern Brazil, from 2001 to 2002 and confirmed in laboratory were studied. Larval density was verified by three indexes: building, recipients and Breteau. The relationship between rainfall, temperature and number of cases was analyzed through Spearman's correlation using time lag. RESULTS: The annual incidence coefficients for 2001 and 2002 were 80.3 and 211.1 per 10,000 inhabitants, respectively. Most dengue cases (n=1,091; 65%) were reported in the district's central area. Females (n=969; 60%) and the age groups 20 to 29 and 30 to 39 years old of both sexes were mostly affected. Significant associations were not observed between climatic variables and the number of dengue cases in the first month; however, this association became evident in the second month throughout the fourth month. CONCLUSIONS: The association between the number of dengue cases and abiotic factors identified the time lag in which rain and temperature favored the occurrence of new cases. These aspects, associated to tourist vulnerability in the coastal area, promoted conditions for dengue occurrence. The urbanization without sanitary infrastructure possibly affected mosquito density and dengue incidence. Such factors may have contributed to mosquito dispersion and dissemination of different dengue serotypes.     

Why dengue haemorrhagic fever in Cuba? 2. An integral analysis

The epidemiological factors present in Cuba in 1981, when the dengue haemorrhagic fever/dengue shock syndrome (DHF/DSS) epidemic occurred, were exceptional when compared to those of other countries in the region. Evidence is presented which demonstrates that virulence of the circulating strain is an important element in the analysis of an epidemic. Although the two current hypotheses to explain the occurrence of DHF/DSS epidemics are valid in well defined but different epidemiological situations, neither Halstead's hypothesis of secondary-type infection or Rosen's hypothesis of the role played by the virulence of the circulating strain can explain all cases. An integrated, multifactorial and unifying hypothesis is presented, which could be applied in different epidemiological situations. It is based mainly on an in-depth analysis of the literature and of the Cuban experience.     

Why dengue haemorrhagic fever in Cuba? 1. Individual risk factors for dengue haemorrhagic fever/dengue shock syndrome (DHF/DSS)

During the dengue haemorrhagic fever/dengue shock syndrome (DHF/DSS) epidemic in Cuba in 1981, we identified some individual risk factors for the development of the severe clinical picture or for the fatal outcome of the disease. The percentage of secondary infection in 3 groups of patients with DHF/DSS was between 95 and 98.3 and it is concluded that secondary infection is an important, but not the only, condition for the development of DHF/DSS. An analysis of these 3 groups of patients and a fourth group of fatal cases showed that chronic diseases such as bronchial asthma, diabetes mellitus and sickle cell anaemia were additional risk factors contributing significantly to the development of DHF/DSS. The study also revealed that race was an individual risk factor, since DHF/DSS was more prevalent in white than in black persons.     

Different clinical and laboratory manifestations between dengue haemorrhagic fever and dengue fever with bleeding tendency

The incidence of dengue fever (DF) is estimated to have increased 30-fold in the past 50 years. The incidence of dengue haemorrhagic fever (DHF), a life-threatening complication of DF, is also increasing. The need for better classification of the severity of dengue infections has been proposed in order to clarify different entities of dengue infections. We defined a class of patients with DF with bleeding tendency (DF w/B) to differentiate further the varying pathogenesis among DF, DF w/B and DHF. In a hospital-based study in Taiwan, we compared clinical features, biochemistry and immune mediators among patients with DHF, DF w/B and DF. Results showed that DF w/B patients, similar to DHF patients, had a higher rate of secondary dengue infection (P<0.001) as well as higher IL-10 (P=0.023) and lower IFNgamma (P=0.009) levels than DF patients. In contrast, DHF patients had significantly higher soluble vascular cell adhesion molecule 1 levels than DF w/B patients (P=0.038) and DF patients (P<0.001). This study provides new insight into the different immune mechanisms of DF, DF w/B and DHF. DF involves a Th1 reaction and DF w/B involves an altered Th2 reaction, whereas DHF involves an altered Th2 reaction and augmented vascular insult.     

气象因素影响登革热传播研究进展

气象因素可以通过影响媒介蚊虫的繁殖和传播等方式,影响登革热的传播。评估气象因素对登革热传播的影响,探讨其影响机制,可以为完善登革热监测系统及进一步采取防治措施提供依据。研究显示,一定条件下,温度、光照、降雨、相对湿度等气象因素与登革热的传播关系密切。某些极端天气事件可以通过影响微小气候等方式影响登革热的传播。因此,在现有登革热监测系统的基础上,建议增加气象因素指标,以提高监测的准确性。     

Serological and virological features of dengue fever and dengue haemorrhagic fever in Thailand from 1999 to 2002

Serological and virological features of dengue fever (DF) and dengue haemorrhagic fever (DHF) in Thailand were analysed in 2715 patients from 1999 to 2002. The illness was caused by DEN-1 in 45%, DEN-2 in 32%, DEN-3 in 18% and DEN-4 in 5% of patients. Almost all of the DHF cases caused by DEN-2 and DEN-4 were in secondary infection, while approximately 20% of the DHF cases caused by DEN-1 and DEN-3 were in primary infection. Male:female ratio and age distribution were not different among four serotypes in primary and secondary infections. These results indicate that DEN-1 and DEN-3 induce DHF in both primary and secondary infections, and suggest that DEN-2 and DEN-4 in Thailand are less likely to cause DHF in primary infections.     

Dot enzyme immunoassay: an alternative diagnostic aid for dengue fever and dengue haemorrhagic fever.

A dot enzyme immunoassay (DEIA) for the detection of antibodies to dengue virus was tested for use as a tool in the presumptive diagnosis of dengue fever and dengue haemorrhagic fever. Paired sera from the following groups of patients were tested using the DEIA and the haemagglutination inhibition (HI) test: those with primary dengue fever; those experiencing a second dengue infection; and febrile patients who did not have dengue. The data obtained show that the DEIA can be effectively used at a serum dilution of 1:1000 to confirm presumptive recent dengue in patients with a second dengue infection. However, demonstration of seroconversion proved necessary for patients with primary dengue. At a serum dilution of 1:1000 the DEIA has a specificity of 97.3%. The role of this simple and rapid test in improving the effectivity of programmes for the control of dengue virus infection is discussed.     

An investigation into the cyclical incidence of dengue fever.

The purpose of this research was to review the topic of dengue fever transmission and investigate the relationship between seasonal temperature fluctuations and cyclical dengue fever incidence. Data from Puerto Rico (1988-1992) were used to test the model proposed. Dengue fever is a viral disease caused by any one of four antigenically distinct serotypes. It is transmitted by Aedes mosquitoes and infects 80 million people per year. Currently, dengue is endemic in specific tropical and subtropical regions worldwide and epidemic dengue has been reported in the Americas, Asia and some Pacific Islands. Data for Puerto Rico were collected from the NCDC/NOAA and a study conducted by Perez et al. (1994). Multivariate linear regression analysis was used to determine if a relationship exists between the monthly mean temperature lagged and the monthly incidence of dengue fever in Puerto Rico. Statistical significance was achieved and a second-order model produced an R2 of 0.71. A residual analysis reveals positive autocorrelation, thus weakening the model's power to predict monthly dengue incidence. This suggests that other forces or factors related to the history of the herd immunity, the introduction of a new serotype, or demographic transitions are also influencing the cyclical transmission of dengue fever. Case clustering information, regional dengue distributions, and population density transformations must also be obtained in order to assess the forecasting ability of this model. Additional research is needed to avoid oversimplifying the problem. Without such attempts at establishing significant correlations, dengue prevention and control will remain a formidable task for many developing and developed countries.     

Immunological enhancement and the pathogenesis of dengue haemorrhagic fever.

Laboratory studies have provided evidence that the replication of dengue viruses in preparations of primary peripheral blood mononuclear cells of human or simian origin, or in macrophage-like cell lines of human or murine origin, may be enhanced by sub-neutralizing concentrations of homotypic dengue antibody, by heterotypic dengue antibody, or by antibody against heterologous flaviviruses. The mechanism underlying this phenomenon is discussed in the context of dengue haemorrhagic fever and the dengue shock syndrome.     

Policymakers' views on dengue fever/dengue haemorrhagic fever and the need for dengue vaccines in four southeast Asian countries

A survey of policymakers and other influential professionals in four southeast Asian countries (Cambodia, Indonesia, Philippines and Vietnam) was conducted to determine policymakers' views on the public health importance of dengue fever and dengue haemorrhagic fever (DHF), the need for a vaccine and the determinants influencing its potential introduction. The survey, which involved face-to-face interviews with policymakers, health programme managers, researchers, opinion leaders and other key informants, revealed an almost uniformly high level of concern about dengue fever/DHF and a high perceived need for a dengue vaccine. Several characteristics of the disease contribute to this high sense of priority, including its geographic spread, occurrence in outbreaks, the recurrent risk of infection each dengue season, its severity and the difficulty in diagnosis and management, its urban predominance, its burden on hospitals, and its economic toll on governments and families. Research felt to be key to future decision-making regarding dengue vaccine introduction include: disease surveillance studies, in-country vaccine trials or pilot projects, and studies on the economic burden of dengue and the cost-effectiveness of dengue vaccines. The results suggest favourable conditions for public and private sector markets for dengue vaccines and the need for creative financing strategies to ensure their accessibility to poor children in dengue-endemic countries.     

Four dengue virus serotypes found circulating during an outbreak of dengue fever and dengue haemorrhagic fever in Jakarta, Indonesia, during 2004

Periodic outbreaks of dengue have emerged in Indonesia since 1968, with the severity of resulting disease increasing in subsequent years. In early 2004, a purported dengue outbreak erupted across the archipelago, with over 50,000 cases and 603 deaths reported. To confirm the disease aetiology and to provide an epidemiological framework of this epidemic, an investigation was conducted in ten hospitals within the capital city of Jakarta. Clinical and laboratory findings were determined from a cohort of 272 hospitalised patients. Exposure to dengue virus was determined in 180 (66.2%) patients. When clinically assessed, 100 (55.6%) of the 180 patients were classified as having dengue fever (DF), 31 (17.2%) as DF with haemorrhagic manifestations and 49 (27.2%) as dengue haemorrhagic fever (DHF). Evidence from haemagglutination inhibition assays suggested that 33/40 (82.5%) of those with DHF from which laboratory evidence was available suffered from a secondary dengue infection. All four dengue viruses were identified upon viral isolation, with DEN-3 being the most predominant serotype recovered, followed by DEN-4, DEN-2 and DEN-1. In summary, the 2004 outbreak of dengue in Jakarta, Indonesia, was characterised by the circulation of multiple virus serotypes and resulted in a relatively high percentage of a representative population of hospitalised patients developing DHF.     

揭阳口岸登革热媒介密度及与气候因素相关分析

目的了解揭阳口岸登革热媒介伊蚊密度与季节消长及其与气候变化的关系,为防控提供科学依据。方法采用人工小时法和集卵器法调查蚊虫密度,应用SPSS分析季节和气候变化与蚊虫密度的关系。结果 2008-2010年每年5-10月份白纹伊蚊月平均密度为2～29.8只/人工小时;诱卵阳性指数为13.3～86.7;伊蚊密度与诱蚊指数存在正线性相关关系,伊蚊密度与月平均气温及前2个月降雨量呈正线性相关。结论揭阳口岸白纹伊蚊密度较高,与月平均气温有正线性相关,月降雨量对蚊虫密度有滞后正效性关系。     

基于遥感与地理信息技术的登革热环境风险因子标识

目的通过分析广州市2002年登革热疫情数据,采用遥感以及地理信息系统技术标识与登革热（DF）的流行风险相关的地表景观种类。方法首先,通过基于泊松模型的回顾式空间-时间分析方法获取疫情数据的时空聚集状况。其后,从MODIS卫星图像中提取地表景观信息,并逐月逐区计算各地类所占对应研究区的面积比例。最终,由广义线性模型分析确定DF病例的存在与否与地表景观种类面积比例的关系,并使用二态逻辑回归分析建立预测模型。结果最有可能的登革热聚集圈中心位于东山区,同时覆盖越秀区以及荔湾区,其时间窗为8月至10月。最佳预测模型对＂某行政区在气候条件允许下是否存在登革热病例＂的预测达到了91.1%的准确度。结论开放水域,以沼泽和湿地为主的湿草场,以水稻为主的农田以及开发用地被标识为与登革热病例存在与否最为相关的地类因子。     

Geographical gradient of mean age of dengue haemorrhagic fever patients in northern Thailand

Dengue haemorrhagic fever (DHF) is caused by dengue virus transmitted by Aedes mosquitoes; mean age of patients varies temporally and geographically. Variability in age of patients may be due to differences in transmission intensity or demographic structure. To compare these two hypotheses, the mean age of DHF patients from 90 districts in northern Thailand (1994-1996, 2002-2004) was regressed against (i) Aedes abundance or (ii) demographic variables (birthrate, average age) of the district. We also developed software to quantify direction and strength of geographical gradients of these variables. We found that, after adjusting for socioeconomics, climate, spatial autocorrelation, the mean age of patients was correlated only with Aedes abundance. The geographical gradient of mean age of patients originated from entomological, climate, and socioeconomic gradients. Vector abundance was a stronger determinant of mean age of patients than demographic variables, in northern Thailand.     

Pathogenetic mechanisms in dengue haemorrhagic fever: Report of an international collaborative study

In a study of 55 persons with dengue haemorrhagic fever—36 of whom showed the dengue shock syndrome—clinical, haematological, virological, and serological changes were correlated with serial measurements of complement components and immunopathological studies. Viruses dengue-1 or dengue-2 were isolated from the sera of 9 patients. Serological responses indicative of secondary dengue virus infections were observed in 53 patients; 2 (infants) had primary infections. During the acute phase of the disease, dengue antibody titres rose logarithmically. Marked depression of complement components, especially C3, was observed. Activation of both the classical and alternative complement pathways was demonstrated, with depression of both C4 and C3 proactivator levels in most instances, although in some cases it appeared that one mechanism was involved to a greater extent than the other. The level of depression of C3 was correlated with the severity of the disease. Relatively stable transferrin levels indicated that depletion of complement proteins was not primarily due to extravasation. Fibrinogen levels were depressed and fibrinogen split products were found in the plasma. The accumulated data provide further evidence of the central role that activated complement components play in the pathogenesis of dengue haemorrhagic fever.     

猩红热的发病率与气象因素的负二项回归分析

目的通过负二项回归模型探讨气象因素与猩红热发病的关系。方法对1985—2005年安徽省某市猩红热月平均发病率和月平均降水量、月平均气压、月平均气温、月平均相对湿度、月平均最低气温5项气象资料的数据进行描述性分析,然后拟合负二项回归模型,并且对2006年每个月份的发病率做一个预测。结果模型的超离散度K=0．41（95％CI：0．32-0．53）,进行似然比）x2检验x2=306．42,P〈0．001,认为发现负二项回归是适合的模型。猩红热的发生与月平均气压、月平均相对湿度和月平均最低气温有统计学意义（均有P〈0．05）。对2006年各个月份的月发病率预测的结果表明（Wilcoxon符号秩和检验,Z=0．24,P=0．814）,预测值与实际值之间差异无统计学意义,提示预测效果比较理想。结论通过拟合负二项回归模型发现,对猩红热的发生和预测,月平均气压、月平均相对湿度和月平均最低气温是不可忽略的气象因素。