Reemergence of dengue in Cuba: a 1997 epidemic in Santiago de Cuba

Dengue Vaccine: Recommendations of the Advisory Committee on Immunization Practices, United States, 2021

Dengue is a vectorborne infectious disease caused by dengue viruses (DENVs), which are predominantly transmitted by Aedes aegypti and Aedes albopictus mosquitos. Dengue is caused by four closely related viruses (DENV-1–4), and a person can be infected with each serotype for a total of four infections during their lifetime. Areas where dengue is endemic in the United States and its territories and freely associated states include Puerto Rico, American Samoa, the U.S. Virgin Islands, the Federated States of Micronesia, the Republic of Marshall Islands, and the Republic of Palau. This report summarizes the recommendations of the Advisory Committee on Immunization Practices (ACIP) for use of the Dengvaxia vaccine in the United States. The vaccine is a live-attenuated, chimeric tetravalent dengue vaccine built on a yellow fever 17D backbone. Dengvaxia is safe and effective in reducing dengue-related hospitalizations and severe dengue among persons who have had dengue infection in the past. Previous natural infection is important because Dengvaxia is associated with an increased risk for severe dengue in those who experience their first natural infection (i.e., primary infection) after vaccination. Dengvaxia was licensed by the Food and Drug Administration for use among children and adolescents aged 9–16 years (referred to in this report as children). ACIP recommends vaccination with Dengvaxia for children aged 9–16 having evidence of a previous dengue infection and living in areas where dengue is endemic. Evidence of previous dengue infection, such as detection of anti-DENV immunoglobulin G with a highly specific serodiagnostic test, will be required for eligible children before vaccination.

Targeted outdoor residual spraying, autodissemination devices and their combination against Aedes mosquitoes: field implementation in a Malaysian urban setting

Currently, dengue control relies largely on reactive vector control programmes. Proactive vector-control using a rational, well-balanced integrated vector management approach may prove more successful for dengue control. As part of the development of a cluster randomized controlled epidemiological trial, a study was conducted in Johor Bahru, Malaysia. The study included one control site (three buildings) and three intervention sites which were treated as follows: targeted outdoor residual spraying only (TORS site, two buildings); deployment of autodissemination devices only (ADD site, four buildings); and the previous two treatments combined (TORS + ADD site, three buildings). The primary entomological measurement was per cent of positive ovitraps-ovitrap index (OI). The effect of each intervention on OI was analyzed by a modified ordinary least squares regression model. Relative to the control site, the TORS and ADD sites showed a reduction in the Aedes OI (-6.5%, P = 0.04 and -8.3%, P = 0.10, respectively). Analysis by species showed that, relative to control, the Ae. aegypti OI was lower in ADD (-8.9%, P = 0.03) and in TORS (-10.4%, P = 0.02). No such effect was evident in the TORS + ADD site. The present study provides insights into the methods to be used for the main trial. The combination of multiple insecticides with different modes of action in one package is innovative, although we could not demonstrate the additive effect of TORS + ADD. Further work is required to strengthen our understanding of how these interventions impact dengue vector populations and dengue transmission.

Malathion insecticide resistance in Aedes aegypti: laboratory conditions and in situ experimental approach through adult entomological surveillance

OBJECTIVE

In Brazil, the most common method of controlling outbreaks of arbovirus is by the use of chemical sprays, which kill the insect vector, Aedes aegypti. The main objective of this study was to evaluate the resistance of Ae. aegypti to the insecticide, malathion, in situ. The location of this study was the municipality of Foz do Iguaçu, in the state of Paraná, Brazil.

METHODS

Ultra-low-volume (ULV) fogging equipment was used, by vehicle, to apply the insecticide in situ, and mosquito populations after treatment were compared with those of control areas. The resistance of strains collected from the municipality was compared to the Rockefeller strain under laboratory conditions.

RESULTS

We found 220 adult female specimens and 7423 eggs of Ae. aegypti in the areas subjected to UBV treatment, whereas 245 adult females and 10 557 eggs were found in the control areas. The UBV treatment area showed no significant difference compared to the control area, for all the indices. Mortality of the Rockefeller colony varied more quickly when there were slight variations in malathion concentration than the Foz do Iguaçu population.

The Clinical Features of Co-circulating Dengue Viruses and the Absence of Dengue Hemorrhagic Fever in Pakistan

Dengue virus (DENV) is the most common and widespread arboviral infection worldwide. Though all four DENV serotypes cocirculate in nature, the clinicopathological framework of these serotypes is undefined in Pakistan. A cross-sectional, observational study was performed to document the circulation of various arboviruses in the Sindh region of Pakistan. Here we describe a population of patients diagnosed with DENV spanning a 2-year period. This study used an orthogonal system of NS1 antigen ELISA followed by RT-PCR for DENV detection and subtyping. A total of 168 NS1 positive patients were evaluated of which 91 patients were serotyped via RT-PCR. There was no significant difference between sex or age for infection risk and peak transmission occurred during the Autumn months. DENV2 was the most common serotype followed by DENV1 then DENV3, then DENV4. The data show that DENV1 patients were more likely to have abnormal liver function tests; DENV2 infected patients were more likely to exhibit arthralgia and neurological symptoms; DENV3 patients were more likely to complain of burning micturition and have elevated lymphocyte counts and low hematocrit; and DENV4 patients were more likely to report headaches and rash. Notably, no dengue hemorrhagic fever or other manifestations of severe dengue fever were present in patients with primary or secondary infections. We were able to identify significantly more NS1 antigen positive patients than RT-PCR. This study demonstrates that all four DENV serotypes are co-circulating and co-infecting in Pakistan.

Prevalence and Distribution of Dengue Virus in Aedes aegypti in Yogyakarta City before Deployment of Wolbachia Infected Aedes aegypti

Indonesia is one of the countries where dengue infection is prevalent. In this study we measure the prevalence and distribution of dengue virus (DENV) DENV-infected Aedes aegypti in Yogyakarta City, Indonesia, during the wet season when high dengue transmission period occurred, as baseline data before implementation of a Wolbachia-infected Aedes aegypti trial for dengue control. We applied One-Step Multiplex Real Time PCR (RT-PCR) for the type-specific-detection of dengue viruses in field-caught adult Aedes aegypti mosquitoes. In a prospective field study conducted from December 2015 to May 2016, adult female Aedes aegypti were caught from selected areas in Yogyakarta City, and then screened by using RT-PCR. During the survey period, 36 (0.12%) mosquitoes from amongst 29,252 female mosquitoes were positive for a DENV type. In total, 22.20% of dengue-positive mosquitoes were DENV-1, 25% were DENV-2, 17% were DENV-3, but none were positive for DENV-4. This study has provided dengue virus infection prevalence in field-caught Aedes aegypti and its circulating serotype in Yogyakarta City before deployment of Wolbachia-infected Aedes aegypti.

History of ZIKV Infections in India and Management of Disease Outbreaks

Zika virus (ZIKV) is an emerging arbovirus infection endemic in multiple countries spread from Asia, Africa to the Americas and Europe. Previously known to cause rare and fairly benign human infections, ZIKV has become a major international public health emergency after being linked to unexpected neurological complications, that includes fetal brain damage/death and microcephaly in babies born to infected mothers and Guillain-Barre syndrome (GBS) in adults. It appears that a single genetic mutation in the ZIKV genome, likely acquired during explosive ZIKV outbreak in French Polynesia (2013), made virus causing mild disease to target fetus brain. The Aedes mosquitoes are found to be the main carrier of ZIKV, passing the virus to humans. Originally isolated from patients in Africa in 1954 (African lineage), virus disseminated to Southeast Asia (Asian lineage), establishing new endemic foci, including one in India. Numerous cases of ZIKV infection have been reported in several locations in India and neighboring countries like Pakistan and Bangladesh since mid of the last century, suggesting that the virus reached this part of Asia soon after it was first discovered in Uganda in 1947. Although, the exact means by which ZIKV was introduced to India remains unknown, it appears that the ZIKV strain circulating in India possibly belongs to the "Asian lineage," which has not yet been associated with microcephaly and other neurological disorders. However, there still exists a threat that the contemporary ZIKV virulent strain from South America, carrying a mutation can return to Asia, posing a potential crisis to newborns and adult patients. Currently there is no specific vaccine or antiviral medication to combat ZIKV infection, thus, vector control and continuous monitoring of potential ZIKV exposure is essential to prevent the devastating consequences similar to the ones experienced in Brazil. However, the major obstacle faced by Indian healthcare agencies is that most cases of ZIKV infection have been reported in rural areas that lack access to rapid diagnosis of infection. In this review, we attempt to present a comprehensive analysis of what is currently known about the ZIKV infection in India and the neighboring countries.

Insecticide treated curtains and residual insecticide treatment to control Aedes aegypti: An acceptability study in Santiago de Cuba

Background

Within the context of a field trial conducted by the Cuban vector control program (AaCP), we assessed acceptability of insecticide-treated curtains (ITCs) and residual insecticide treatment (RIT) with deltamethrin by the community. We also assessed the potential influence of interviewees’ risk perceptions for getting dengue and disease severity.

Methodology/principal findings

We embedded a qualitative study using in-depth interviews in a cluster randomized trial (CRT) testing the effectiveness of ITCs and RIT in Santiago de Cuba. In-depth interviews (N = 38) were conducted four and twelve months after deployment of the tools with people who accepted the tools, who stopped using them and who did not accept the tools. Data analysis was deductive. Main reasons for accepting ITCs at the start of the trial were perceived efficacy and not being harmful to health. Constraints linked to manufacturer instructions were the main reason for not using ITCs. People stopped using the ITCs due to perceived allergy, toxicity and low efficacy. Few heads of households refused RIT despite the noting reasons for rejection, such as allergy, health hazard and toxicity. Positive opinions of the vector control program influenced acceptability of both tools. However, frequent insecticide fogging as part of routine AaCP vector control actions diminished perceived efficacy of both tools and, therefore, acceptability. Fifty percent of interviewees did feel at risk for getting dengue and considered dengue a severe disease. However, this did not appear to influence acceptability of ITCs or RIT.

Conclusion/significance

Acceptability of ITCs and RIT was linked to acceptability of AaCP routine vector control activities. However, uptake and use were not always an indication of acceptability. Factors leading to acceptability may be best identified using qualitative methods, but more research is needed on the concept of acceptability and its measurement.

We aimed to understand what makes insecticide-treated curtains (ITCs) and residual insecticide treatment (RIT) with deltamethrin acceptable or not to users of these tools. In-depth interviews were conducted as part of a field trial conducted by the Cuban vector control program (AaCP) to test the effectiveness of these tools in Santiago de Cuba. Perceived efficacy was the main reason for interviewees who accepted the tools. Constraints linked to manufacturer instructions were the main reason for not using the ITCs when offered at the start of the trial. People stopped using the ITCs due to perceived allergy, toxicity and low efficacy. Few heads of households refused RIT despite identifying various reasons for rejection, such as allergy, health hazard and toxicity. Positive opinions of the Cuban vector control program influenced acceptability of both tools. On the contrary, perceptions of dengue risk did not appear to influence acceptability of ITCs or RIT. Our findings add on the importance of the growing body of qualitative research assessing acceptability of health interventions.

Association of Single-Nucleotide Polymorphisms in Immune-Related Genes with Development of Dengue Hemorrhagic Fever in a Mexican Population

Single-nucleotide polymorphisms (SNPs) occurring in immune-related genes have been associated with risk or protection for development of dengue, depending on ethnicity. Here, we genotyped seven SNPs located in immune response-related genes to identify their association with severe forms of dengue in patients from an endemic region in Mexico. One hundred and thirty-eight patients with dengue fever (DF), thirty-one dengue hemorrhagic fever (DHF) patients, as well as 304 healthy donors were genotyped by using a TaqMan-based approach. SNP analysis, including rs1800629 (TNF), rs4804803 (CD209), rs2780831 (JAK1), rs1801274 (FCGR2A), rs231775 (CTLA4), rs12979860, and rs8099917 (IFNL3), was performed. The rs1800629 A-allele in the TNF gene was associated with an increased risk of DHF (OR = 3.4, CI = 1.235-9.284 p = 0.0212) whereas SNPs rs4804803, rs2780831, rs1801274, rs231775, rs12979860, and rs8099917 showed no association in this cohort. These results show that allelic variations in TNF can play an important role in the development of DHF. However, the lack of association between all remaining SNPs and DHF suggests that the genetic background might directly modify the role of these immune-related molecules, leading to the milder illness often observed in a Mexican population.

Increased efficiency in the second-hand tire trade provides opportunity for dengue control

Dengue fever is increasing in geographical range, spread by invasion of its vector mosquitoes. The trade in second-hand tires has been implicated as a factor in this process because they act as mobile reservoirs of mosquito eggs and larvae. Regional transportation of tires can create linkages between rural areas with dengue and disease-free urban areas, potentially giving rise to outbreaks even in areas with strong local control measures. In this work we sought to model the dynamics of mosquito transportation via the tire trade, in particular to predict its role in causing unexpected dengue outbreaks through vertical transmission of the virus across generations of mosquitoes. We also aimed to identify strategies for regulating the trade in second-hand tires, improving disease control. We created a mathematical model which captures the dynamics of dengue between rural and urban areas, taking into account the movement and storage time of tires, and mosquito diapause. We simulate a series of scenarios in which a mosquito population is introduced to a dengue-free area via movement of tires, either as single or multiple events, increasing the likelihood of a dengue outbreak. A persistent disease state can be induced regardless of whether urban conditions for an outbreak are met, and an existing endemic state can be enhanced by vector input. Finally we assess the potential for regulation of tire processing as a means of reducing the transmission of dengue fever using a specific case study from Puerto Rico. Our work demonstrates the importance of the second-hand tire trade in modulating the spread of dengue fever across regions, in particular its role in introducing dengue to disease-free areas. We propose that reduction of tire storage time and control of their movement can play a crucial role in containing dengue outbreaks.

Implication of vaccination against dengue for Zika outbreak

Zika virus co-circulates with dengue in tropical and sub-tropical regions. Cases of co-infection by dengue and Zika have been reported, the implication of this co-infection for an integrated intervention program for controlling both dengue and Zika must be addressed urgently. Here, we formulate a mathematical model to describe the transmission dynamics of co-infection of dengue and Zika with particular focus on the effects of Zika outbreak by vaccination against dengue among human hosts. Our analysis determines specific conditions under which vaccination against dengue can significantly increase the Zika outbreak peak, and speed up the Zika outbreak peak timing. Our results call for further study about the co-infection to direct an integrated control to balance the benefits for dengue control and the damages of Zika outbreak.

Dengue Contingency Planning: From Research to Policy and Practice

BACKGROUND

Dengue is an increasingly incident disease across many parts of the world. In response, an evidence-based handbook to translate research into policy and practice was developed. This handbook facilitates contingency planning as well as the development and use of early warning and response systems for dengue fever epidemics, by identifying decision-making processes that contribute to the success or failure of dengue surveillance, as well as triggers that initiate effective responses to incipient outbreaks.

METHODOLOGY/PRINCIPAL FINDINGS

Available evidence was evaluated using a step-wise process that included systematic literature reviews, policymaker and stakeholder interviews, a study to assess dengue contingency planning and outbreak management in 10 countries, and a retrospective logistic regression analysis to identify alarm signals for an outbreak warning system using datasets from five dengue endemic countries. Best practices for managing a dengue outbreak are provided for key elements of a dengue contingency plan including timely contingency planning, the importance of a detailed, context-specific dengue contingency plan that clearly distinguishes between routine and outbreak interventions, surveillance systems for outbreak preparedness, outbreak definitions, alert algorithms, managerial capacity, vector control capacity, and clinical management of large caseloads. Additionally, a computer-assisted early warning system, which enables countries to identify and respond to context-specific variables that predict forthcoming dengue outbreaks, has been developed.

CONCLUSIONS/SIGNIFICANCE

Most countries do not have comprehensive, detailed contingency plans for dengue outbreaks. Countries tend to rely on intensified vector control as their outbreak response, with minimal focus on integrated management of clinical care, epidemiological, laboratory and vector surveillance, and risk communication. The Technical Handbook for Surveillance, Dengue Outbreak Prediction/ Detection and Outbreak Response seeks to provide countries with evidence-based best practices to justify the declaration of an outbreak and the mobilization of the resources required to implement an effective dengue contingency plan.

Assessing the global threat from Zika virus

First discovered in 1947, Zika virus (ZIKV) infection remained a little-known tropical disease until 2015, when its apparent association with a considerable increase in the incidence of microcephaly in Brazil raised alarms worldwide. There is limited information on the key factors that determine the extent of the global threat from ZIKV infection and resulting complications. Here, we review what is known about the epidemiology, natural history, and public health effects of ZIKV infection, the empirical basis for this knowledge, and the critical knowledge gaps that need to be filled.

A critical assessment of vector control for dengue prevention

Recently, the Vaccines to Vaccinate (v2V) initiative was reconfigured into the Partnership for Dengue Control (PDC), a multi-sponsored and independent initiative. This redirection is consistent with the growing consensus among the dengue-prevention community that no single intervention will be sufficient to control dengue disease. The PDC's expectation is that when an effective dengue virus (DENV) vaccine is commercially available, the public health community will continue to rely on vector control because the two strategies complement and enhance one another. Although the concept of integrated intervention for dengue prevention is gaining increasingly broader acceptance, to date, no consensus has been reached regarding the details of how and what combination of approaches can be most effectively implemented to manage disease. To fill that gap, the PDC proposed a three step process: (1) a critical assessment of current vector control tools and those under development, (2) outlining a research agenda for determining, in a definitive way, what existing tools work best, and (3) determining how to combine the best vector control options, which have systematically been defined in this process, with DENV vaccines. To address the first step, the PDC convened a meeting of international experts during November 2013 in Washington, DC, to critically assess existing vector control interventions and tools under development. This report summarizes those deliberations.

Dengue disease surveillance: an updated systematic literature review

OBJECTIVES

To review the evidence for the application of tools for dengue outbreak prediction/detection and trend monitoring in passive and active disease surveillance systems in order to develop recommendations for endemic countries and identify important research needs.

METHODS

This systematic literature review followed the protocol of a review from 2008, extending the systematic search from January 2007 to February 2013 on PubMed, EMBASE, CDSR, WHOLIS and Lilacs. Data reporting followed the PRISMA statement. The eligibility criteria comprised (i) population at risk of dengue, (ii) dengue disease surveillance, (iii) outcome of surveillance described and (iv) empirical data evaluated. The analysis classified studies based on the purpose of the surveillance programme. The main limitation of the review was expected publication bias.

RESULTS

A total of 1116 papers were identified of which 36 articles were included in the review. Four cohort-based prospective studies calculated expansion factors demonstrating remarkable levels of underreporting in the surveillance systems. Several studies demonstrated that enhancement methods such as laboratory support, sentinel-based reporting and staff motivation contributed to improvements in dengue reporting. Additional improvements for passive surveillance systems are possible by incorporating simple data forms/entry/electronic-based reporting; defining clear system objectives; performing data analysis at the lowest possible level (e.g. district); seeking regular data feedback. Six studies showed that serotype changes were positively correlated with the number of reported cases or with dengue incidence, with lag times of up to 6 months. Three studies found that data on internet searches and event-based surveillance correlated well with the epidemic curve derived from surveillance data.

CONCLUSIONS

Passive surveillance providing the baseline for outbreak alert should be strengthened and appropriate threshold levels for outbreak alerts investigated. Additional enhancement tools such as syndromic surveillance, laboratory support and motivation strategies can be added. Appropriate alert signals need to be identified and integrated into a risk assessment tool. Shifts in dengue serotypes/genotype or electronic event-based surveillance have also considerable potential as indicator in dengue surveillance. Further research on evidence-based response strategies and cost-effectiveness is needed.

A shorter time interval between first and second dengue infections is associated with protection from clinical illness in a school-based cohort in Thailand

BACKGROUND

Despite the strong association between secondary dengue virus (DENV) infections and dengue hemorrhagic fever (DHF), the majority of secondary infections are subclinical or mild. The determinants of clinical severity remain unclear, though studies indicate a titer-dependent and time-dependent role of cross-protective anti-DENV antibodies.

METHODS

Data from 2 sequential prospective cohort studies were analyzed for subclinical and symptomatic DENV infections in schoolchildren in Kamphaeng Phet, Thailand (1998-2002 and 2004-2007). Children experiencing ≥ 1 DENV infection were selected as the population for analysis (contributing 2169 person-years of follow-up).

RESULTS

In total, 1696 children had ≥ 1 DENV infection detected during their enrollment; 268 experienced 2 or more infections. A shorter time interval between infections was associated with subclinical infection in children seronegative for DENV at enrollment, for whom a second-detected DENV infection is more likely to reflect a true second infection (average of 2.6 years between infections for DHF, 1.9 for DF, and 1.6 for subclinical infections).

CONCLUSIONS

These findings support a pathogenesis model where cross-reactive antibodies wane from higher-titer, protective levels to lower-titer, detrimental levels. This is one of the first studies of human subjects to suggest a window of cross-protection following DENV infection since Sabin's challenge studies in the 1940s.

Understanding the dengue viruses and progress towards their control

Traditionally, the four dengue virus serotypes have been associated with fever, rash, and the more severe forms, haemorrhagic fever and shock syndrome. As our knowledge as well as understanding of these viruses increases, we now recognise not only that they are causing increasing numbers of human infections but also that they may cause neurological and other clinical complications, with sequelae or fatal consequences. In this review we attempt to highlight some of these features in the context of dengue virus pathogenesis. We also examine some of the efforts currently underway to control this "scourge" of the tropical and subtropical world.

Secondary infection as a risk factor for dengue hemorrhagic fever/dengue shock syndrome: an historical perspective and role of antibody-dependent enhancement of infection

Today, dengue viruses are the most prevalent arthropod-borne viruses in the world. Since the 1960s, numerous reports have identified a second heterologous dengue virus (DENV) infection as a principal risk factor for severe dengue disease (dengue hemorrhagic fever/dengue shock syndrome, DHF/DSS). Modifiers of dengue disease response include the specific sequence of two DENV infections, the interval between infections, and contributions from the human host, such as age, ethnicity, chronic illnesses and genetic background. Antibody-dependent enhancement (ADE) of dengue virus infection has been proposed as the early mechanism underlying DHF/DSS. Dengue cross-reactive antibodies raised following a first dengue infection combine with a second infecting virus to form infectious immune complexes that enter Fc-receptor-bearing cells. This results in an increased number of infected cells and increased viral output per cell. At the late illness stage, high levels of cytokines, possibly the result of T cell elimination of infected cells, result in vascular permeability, leading to shock and death. This review is focused on the etiological role of secondary infections (SI) and mechanisms of ADE.

Diffusion of community empowerment strategies for Aedes aegypti control in Cuba: a muddling through experience

Effective participatory strategies in dengue control have been developed and assessed as small-scale efforts. The challenge is to scale-up and institutionalize these strategies within dengue control programs. We describe and critically analyze the diffusion process of an effective empowerment strategy within the Cuban Aedes aegypti control program, focusing on decision-making at the national level, to identify ways forward to institutionalize such strategies in Cuba and elsewhere. From 2005 to 2009, we carried out a process-oriented case study. We used participant observation, in-depth interviews with key informants involved in the diffusion process and document analysis. In a first phase, the data analysis was inductive. In a second phase, to enhance robustness of the analysis, emerging categories were contrasted with Rogers' five-stage conceptual model of the innovation-decision process, which was eventually used as the analytical framework. The diffusion of the empowerment strategy was a continuous and dynamic process. Adoption was a result of the perceived potential match between the innovative empowerment strategy and the performance gap of the Ae. aegypti control program. During implementation, the strategy was partially modified by top level Ae. aegypti control program decision-makers to accommodate program characteristics. However, structure, practices and organizational culture of the control program did not change significantly. Thus rejection occurred. It was mainly due to insufficient dissemination of know-how and underlying principles of the strategy by innovation developers, but also to resistance to change. The innovation-diffusion process has produced mitigated results to date, and the control program is still struggling to find ways to move forward. Improving the innovation strategy by providing the necessary knowledge about the innovation and addressing control program organizational changes is crucial for successful diffusion of empowerment strategies. Issues highlighted in this particular experience might be relevant in the innovation-diffusion process of other complex innovations within health systems.

Lessons from malaria control to help meet the rising challenge of dengue

Achievements in malaria control could inform efforts to control the increasing global burden of dengue. Better methods for quantifying dengue endemicity-equivalent to parasite prevalence surveys and endemicity mapping used for malaria-would help target resources, monitor progress, and advocate for investment in dengue prevention. Success in controlling malaria has been attributed to widespread implementation of interventions with proven efficacy. An improved evidence base is needed for large-scale delivery of existing and novel interventions for vector control, alongside continued investment in dengue drug and vaccine development. Control of dengue is unlikely to be achieved without coordinated international financial and technical support for national programmes, which has proven effective in reducing the global burden of malaria.

Dynamic epidemiological models for dengue transmission: a systematic review of structural approaches

Dengue is a vector-borne disease recognized as the major arbovirose with four immunologically distant dengue serotypes coexisting in many endemic areas. Several mathematical models have been developed to understand the transmission dynamics of dengue, including the role of cross-reactive antibodies for the four different dengue serotypes. We aimed to review deterministic models of dengue transmission, in order to summarize the evolution of insights for, and provided by, such models, and to identify important characteristics for future model development. We identified relevant publications using PubMed and ISI Web of Knowledge, focusing on mathematical deterministic models of dengue transmission. Model assumptions were systematically extracted from each reviewed model structure, and were linked with their underlying epidemiological concepts. After defining common terms in vector-borne disease modelling, we generally categorised fourty-two published models of interest into single serotype and multiserotype models. The multi-serotype models assumed either vector-host or direct host-to-host transmission (ignoring the vector component). For each approach, we discussed the underlying structural and parameter assumptions, threshold behaviour and the projected impact of interventions. In view of the expected availability of dengue vaccines, modelling approaches will increasingly focus on the effectiveness and cost-effectiveness of vaccination options. For this purpose, the level of representation of the vector and host populations seems pivotal. Since vector-host transmission models would be required for projections of combined vaccination and vector control interventions, we advocate their use as most relevant to advice health policy in the future. The limited understanding of the factors which influence dengue transmission as well as limited data availability remain important concerns when applying dengue models to real-world decision problems.

Need for an efficient adult trap for the surveillance of dengue vectors

The emergence and re-emergence of arboviral diseases transmitted by Aedes aegypti and Ae. albopictus continue to be a major threat in the tropics and subtropics. Associations between currently used indices and dengue transmission have not been proven to be satisfactorily predictive of dengue epidemics. Classical larval indices in dengue surveillance have limited use in assessing transmission risk and are a poor proxy for measuring adult emergence. Besides, collection of larval indices is labour intensive and plagued by difficulties of access particularly in urban settings. The re-emergence of dengue disease in many countries despite lower immature indices has warranted the need for more effective indices in dengue vector surveillance and control. Reliable and highly useful indices could be developed with the help of efficient and appropriate entomological tools. Most current programmes emphasize reduction of immature Ae. aegypti density, but it is of little value because its relation to transmission risk is weak. More attention should be paid to methods directed toward adult rather than immature Ae. aegypti. Collection of sufficient numbers of adult mosquitoes is important to understand disease transmission dynamics and to devise an appropriate control strategy. Even though, use of certain traps such as BG-Sentinel traps has been attempted in monitoring Ae. aegypti population, their utility is limited due to various setbacks which make these insufficient for entomological and epidemiological studies. Thus, there is an urgent need for the development of an ideal trap that could be used for adult vector surveillance. The present review critically analyzes the setbacks in the existing tools of entomological surveillance of dengue vectors and highlights the importance and necessity of more improved, more sensitive and reliable adult trap that could be used for surveillance of dengue vectors.

Dengue vector surveillance programs: a review of methodological diversity in some endemic and epidemic countries

Vector surveillance is a cornerstone of dengue management yet there is a diversity of surveillance programs evident internationally. Such diversity is described in this review to enable a broader assessment of dengue vector surveillance methods. This review describes the diversity of surveillance programs for dengue vectors in several endemic and epidemic countries. Furthermore, strengths and weaknesses of vector surveillance methods, including larval surveys, BG-Sentinel trap, and autocidal and sticky ovitraps, are also discussed. The ability to compare and contrast these programs could contribute to the finding of better methods both locally and nationally and facilitate interregional technology transfer. Health authorities in both endemic and epidemic countries alike could benefit from adopting technologies and practices from other regions.

Fatal dengue hemorrhagic fever in adults: emphasizing the evolutionary pre-fatal clinical and laboratory manifestations

Background

A better description of the clinical and laboratory manifestations of fatal patients with dengue hemorrhagic fever (DHF) is important in alerting clinicians of severe dengue and improving management.

Methods and Findings

Of 309 adults with DHF, 10 fatal patients and 299 survivors (controls) were retrospectively analyzed. Regarding causes of fatality, massive gastrointestinal (GI) bleeding was found in 4 patients, dengue shock syndrome (DSS) alone in 2; DSS/subarachnoid hemorrhage, Klebsiella pneumoniae meningitis/bacteremia, ventilator associated pneumonia, and massive GI bleeding/Enterococcus faecalis bacteremia each in one. Fatal patients were found to have significantly higher frequencies of early altered consciousness (≤24 h after hospitalization), hypothermia, GI bleeding/massive GI bleeding, DSS, concurrent bacteremia with/without shock, pulmonary edema, renal/hepatic failure, and subarachnoid hemorrhage. Among those experienced early altered consciousness, massive GI bleeding alone/with uremia/with E. faecalis bacteremia, and K. pneumoniae meningitis/bacteremia were each found in one patient. Significantly higher proportion of bandemia from initial (arrival) laboratory data in fatal patients as compared to controls, and higher proportion of pre-fatal leukocytosis and lower pre-fatal platelet count as compared to initial laboratory data of fatal patients were found. Massive GI bleeding (33.3%) and bacteremia (25%) were the major causes of pre-fatal leukocytosis in the deceased patients; 33.3% of the patients with pre-fatal profound thrombocytopenia (<20000/µL), and 50% of the patients with pre-fatal prothrombin time (PT) prolongation experienced massive GI bleeding.

Conclusions

Our report highlights causes of fatality other than DSS in patients with severe dengue, and suggested hypothermia, leukocytosis and bandemia may be warning signs of severe dengue. Clinicians should be alert to the potential development of massive GI bleeding, particularly in patients with early altered consciousness, profound thrombocytopenia, prolonged PT and/or leukocytosis. Antibiotic(s) should be empirically used for patients at risk for bacteremia until it is proven otherwise, especially in those with early altered consciousness and leukocytosis.

Fatality rate and causes of fatality in dengue-affected patients greatly varied from one reported series to another. A better understanding of the clinical and laboratory manifestations of fatal patients with dengue hemorrhagic fever (DHF) is important in alerting clinicians of severe dengue and improving management. In a retrospective analysis of 10 adults who died of and 299 survived (controls) DHF, dengue shock syndrome (DSS) alone was found in only 20% of dengue-related death, while intractable massive gastrointestinal (GI) bleeding was found in 40%, and DSS with concurrent subarachnoid hemorrhage, intractable massive GI bleeding with concurrent bacteremia, bacterial sepsis/meningitis, and sepsis due to ventilator associated pneumonia each were found in 10%. Early altered consciousness (developed ≤24 h after hospitalization), GI bleeding/massive GI bleeding and concurrent bacteremia were significantly found among the deceased patients. Our data suggest that hypothermia, leukocytosis and bandemia at hospital presentation may be warning signs of severe dengue. Clinicians should be alert to the potential development of massive GI bleeding, particularly in patients with early altered consciousness, profound thrombocytopenia, prothrombin time prolongation and/or leukocytosis. Antibiotic(s) should be empirically used for patients at risk for bacteremia until it is proven otherwise, especially in those with early altered consciousness and leukocytosis.

Population structure of the dengue viruses, Aragua, Venezuela, 2006-2007. Insights into dengue evolution under hyperendemic transmission

During the past three decades there has been a notable increase in dengue disease severity in Venezuela. Nevertheless, the population structure of the viruses being transmitted in this country is not well understood. Here, we present a molecular epidemiological study on dengue viruses (DENV) circulating in Aragua State, Venezuela during 2006-2007. Twenty-one DENV full-length genomes representing all of the four serotypes were amplified and sequenced directly from the serum samples. Notably, only DENV-2 was associated with severe disease. Phylogenetic trees constructed using Bayesian methods indicated that only one genotype was circulating for each serotype. However, extensive viral genetic diversity was found in DENV isolated from the same area during the same period, indicating significant in situ evolution since the introduction of these genotypes. Collectively, the results suggest that the non-structural (NS) proteins may play an important role in DENV evolution, particularly NS1, NS2A and NS4B proteins. The phylogenetic data provide evidence to suggest that multiple introductions of DENV have occurred from the Latin American region into Venezuela and vice versa. The implications of the significant viral genetic diversity generated during hyperendemic transmission, particularly in NS protein are discussed and considered in the context of future development and use of human monoclonal antibodies as antivirals and tetravalent vaccines.

The complexity of antibody-dependent enhancement of dengue virus infection

Antibody-dependent enhancement (ADE) has been proposed as a mechanism to explain dengue hemorrhagic fever (DHF) in the course of a secondary dengue infection. Very recently, Dejnirattisai et al., 2010 [1], published an important article supporting the involvement of anti-prM antibodies in the ADE phenomenon. The complexity of ADE in the context of a secondary dengue infection is discussed here.

Dengue incidence in urban and rural Cambodia: results from population-based active fever surveillance, 2006-2008

Background

Dengue vaccines are now in late-stage development, and evaluation and robust estimates of dengue disease burden are needed to facilitate further development and introduction. In Cambodia, the national dengue case-definition only allows reporting of children less than 16 years of age, and little is known about dengue burden in rural areas and among older persons. To estimate the true burden of dengue in the largest province of Cambodia, Kampong Cham, we conducted community-based active dengue fever surveillance among the 0-to-19–year age group in rural villages and urban areas during 2006–2008.

Methods and Findings

Active surveillance for febrile illness was conducted in 32 villages and 10 urban areas by mothers trained to use digital thermometers combined with weekly home visits to identify persons with fever. An investigation team visited families with febrile persons to obtain informed consent for participation in the follow-up study, which included collection of personal data and blood specimens. Dengue-related febrile illness was defined using molecular and serological testing of paired acute and convalescent blood samples. Over the three years of surveillance, 6,121 fever episodes were identified with 736 laboratory-confirmed dengue virus (DENV) infections for incidences of 13.4–57.8/1,000 person-seasons. Average incidence was highest among children less than 7 years of age (41.1/1,000 person-seasons) and lowest among the 16-to-19–year age group (11.3/1,000 person-seasons). The distribution of dengue was highly focal, with incidence rates in villages and urban areas ranging from 1.5–211.5/1,000 person-seasons (median 36.5). During a DENV-3 outbreak in 2007, rural areas were affected more than urban areas (incidence 71 vs. 17/1,000 person-seasons, p<0.001).

Conclusion

The large-scale active surveillance study for dengue fever in Cambodia found a higher disease incidence than reported to the national surveillance system, particularly in preschool children and that disease incidence was high in both rural and urban areas. It also confirmed the previously observed focal nature of dengue virus transmission.

Dengue is a major public health problem in South-East Asia. Several dengue vaccine candidates are now in late-stage development and are being evaluated in clinical trials. Accurate estimates of true dengue disease burden will become an important factor in the public-health decision-making process for endemic countries once safe and effective vaccines become available. However, estimates of the true disease incidence are difficult to make, because national surveillance systems suffer from disease under-recognition and reporting. Dengue is mainly reported among children, and in some countries, such as Cambodia, the national case definition only includes hospitalized children. This study used active, community-based surveillance of febrile illness coupled with laboratory testing for DENV infection to identify cases of dengue fever in rural and urban populations. We found a high burden of dengue in young children and late adolescents in both rural and urban communities at a magnitude greater than previously described. The study also confirmed the previously observed focal nature of dengue virus transmission.

An outbreak of dengue fever in St. Croix (US Virgin Islands), 2005

Background

Periodic outbreaks of dengue fever occur in the United States Virgin Islands. In June 2005, an outbreak of dengue virus (DENV) serotype-2 with cases of dengue hemorrhagic fever (DHF) was detected in St. Croix, US Virgin Islands. The objective of this report is to describe this outbreak of DENV-2 and the findings of a case-control study examining risk factors for DHF.

Methodology/Principal Findings

This is the largest dengue outbreak ever recorded in St. Croix, with 331 suspected dengue cases reported island-wide during 2005 (62.2 cases/10,000 population); 54% were hospitalized, 21% had at least one hemorrhagic manifestation, 28% had thrombocytopenia, 5% had DHF and 1 patient died. Eighty-nine laboratory-positive hospitalized patients were identified. Of these, there were 15 (17%) who met the WHO criteria for DHF (cases) and 74 (83%) who did not (controls). The only variable significantly associated with DHF on bivariate or multivariable analysis was age, with an adjusted odds ratio (95% confidence interval) of 1.033 (1.003,1.064).

Conclusions/Significance

During this outbreak of DENV-2, a high proportion of cases developed DHF and increasing age was significantly associated with DHF.

Tumor necrosis factor-alpha, transforming growth factor-β1, and interleukin-10 gene polymorphisms: implication in protection or susceptibility to dengue hemorrhagic fever

Dengue virus infection has emerged as one of the most important arthropod-borne viral diseases. Some dengue infected individuals develop the severe, life-threatening form of the disease, dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Host genetic factors may be relevant and may predispose some individuals to the severe illness. Human leukocyte antigen (HLA), FcγR, tumor necrosis factor (TNF)-α, and dendritic cell-specific intracellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN), among others genes have been associated with the pathogenesis of dengue. Little is known, however, about the predictive value of cytokine genotypes for the clinical outcome of dengue infection. In this study, the TNF-α, interleukin (IL)-6, interferon (IFN)-γ, IL-10 and transforming growth factor (TGF)-β1 gene single nucleotide polymorphisms (SNP) were studied by polymerase chain reaction-sequence-specific primer in a group of individuals with the antecedent of DHF during a secondary infection in the sequence dengue 1/dengue 2. A control group was also included. TNF-α (-308) A allele and IL-10 (-1082/-819/-592) ACC/ATA haplotype were significantly associated with DHF. TNF-α (-308) GG and TGF-β1 (c25) GG genotypes were associated with protection. Our results suggest that genetic predisposition to a high TNF-α production and a low IL-10 production seems to increase the susceptibility to DHF during a secondary dengue 2 infection, whereas TGF-β1 high producers might be protected for developing DHF.

Dengue virus life cycle: viral and host factors modulating infectivity

Dengue virus (DENV 1-4) represents a major emerging arthropod-borne pathogen. All four DENV serotypes are prevalent in the (sub) tropical regions of the world and infect 50-100 million individuals annually. Whereas the majority of DENV infections proceed asymptomatically or result in self-limited dengue fever, an increasing number of patients present more severe manifestations, such as dengue hemorrhagic fever and dengue shock syndrome. In this review we will give an overview of the infectious life cycle of DENV and will discuss the viral and host factors that are important in controlling DENV infection.

MCP-1 and MIP-1α expression in a model resembling early immune response to dengue

Dengue virus has become endemic in most tropical urban areas throughout the world, and DHF has appeared concomitantly with this expansion. The intensity of dengue virus replication during the early stages of infection could determine clinical outcomes; therefore, it is important to understand the impact of dengue virus infection on the earliest immune defense against microbial infection, which also strongly regulates the adaptive immune responses. This study was aimed at evaluating the expression of the CC-chemokines MIP-1α/CCL3 and MCP-1/CCL2 in peripheral blood leukocytes using an ex vivo model resembling dengue infection in vivo, in subjects with a well characterized dengue immune background, due to the exceptional Cuban epidemiological situation in dengue. The expression of IFNγ, TNFα and IL10 was also evaluated, giving insight about the role of MCP-1 and MIP-1α in the interplay between innate and adaptive immunity. From individuals with different dengue immune background after dengue virus challenge, increased and different expression of the chemokines and cytokines studied was verified in peripheral blood mononuclear cells, thus demonstrating that the previous immunity to a dengue virus serotype has a strong influence on the early immune response after dengue re-infection.

Plasma leakage in dengue haemorrhagic fever

Dengue viruses (DENV), a group of four serologically distinct but related flaviviruses, are the cause of one of the most important emerging viral diseases. DENV infections result in a wide spectrum of clinical disease including dengue haemorrhagic fever (DHF), a viral haemorrhagic disease characterised by bleeding and plasma leakage. The characteristic feature of DHF is the transient period of plasma leakage and a haemorrhagic tendency. DHF occurs mostly during a secondary DENV infection. Serotype cross-reactive antibodies and mediators from serotype cross-reactive Dengue-specific T cells have been implicated in the pathogenesis. A complex interaction between virus, host immune response and endothelial cells likely impacts the barrier integrity and functions of endothelial cells leading to plasma leakage. Recently the role of angiogenic factors and the role of dengue virus on endothelial cell transcription and functions have been studied. Insights into the mechanisms that confer protection or cause disease are critical in the development of prophylactic and therapeutic modalities for this important disease.

Secondary heterologous dengue infection risk: Disequilibrium between immune regulation and inflammation?

Increased serum levels of cytokines released by cells of the immune response have been detected in patients suffering from dengue disease. Likewise, secondary infections by a different dengue virus serotype result in a highest risk of development of the severe dengue disease. Both findings suggest that the memory immune response is one of the key players in the pathogenesis of this disease. Here we take advantage of the particular Cuban epidemiological situation in dengue to analyze a broad spectrum of cell-mediated immune response mediators at mRNA and protein level. Evidences for a regulatory immune pattern in homologous (TGF-beta, IL-10) vs. pro-inflammatory pattern (IFN-gamma, TNF-alpha) in heterologous dengue virus re-challenge were found, suggesting a possible association with the higher incidence of severe dengue cases in the latter case.

Intersectoral coordination, community empowerment and dengue prevention: six years of controlled interventions in Playa Municipality, Havana, Cuba

OBJECTIVE

To document the process, outcome and effectiveness of a community-based intervention for dengue control.

METHODS

The primary intervention, focused on strengthening intersectoral coordination, was initiated by researchers in January 2000 in a pilot area in Playa municipality, Havana. In August 2002 health authorities extended the intervention to neighbouring areas, one of which was selected for evaluation. In August 2003 a complementary strategy, focused on community empowerment, was initiated in half of the pilot area. In our control area, routine dengue activities continued throughout the study period. Longitudinal process assessment was carried out using document analysis, interviews and group discussions. Random population surveys in 1999, 2002 and 2005 assessed levels of participation and behavioural changes. Entomological surveillance data from 1999 to 2005 were used to determine effectiveness.

RESULTS

Mean scores for participation in the pilot area were 1.6, 3.4 and 4.4 at baseline, and 2 years after initiating intersectoral coordination and intersectoral coordination plus community empowerment interventions, respectively. While in the control area little behavioural change was observed over time, changes were considerable in the pilot and extension areas, with 80% of households involved in the community empowerment intervention showed adequate behavioural patterns. The pilot and extension areas attained comparable entomological effectiveness with significantly lower Breteau indices (BIs) than the control area. The pilot (sub-) area with the community empowerment intervention reached BIs below 0.1 that continued to be significantly lower than the one in the control area until the end of the study.

CONCLUSION

The study showed a trend in the levels and quality of participation, behavioural change and effectiveness of Aedes control from the routine activities only over an intervention with intersectoral coordination to one that combined intersectoral coordination and community empowerment approach.

[An inter-sector participatory strategy in Cuba using an ecosystem approach to prevent dengue transmission at the local level]

Cuba is located among a group of countries with high dengue incidence. Following several epidemics in the last 10 years, the country designed, implemented, and evaluated a participatory strategy based on the Ecohealth approach. The aim was to promote inter-sector ecosystem management to decrease Aedes aegypti infestation and prevent dengue transmission in the municipality of Cotorro, in Havana city. The study adopted a participatory research methodology. The strategy ensured active participation by the community, diverse sectors, and government in the production of healthy ecosystems. Timely and integrated measures for prevention and control were developed, thereby decreasing the risk of vector proliferation and local dengue transmission. The approach allowed holistic problem analysis, priority setting, and administration of solutions. The strategy has been sustained two years after concluding the process.

Phage-displayed antibody fragments recognizing dengue 3 and dengue 4 viruses as tools for viral serotyping in sera from infected individuals

The current study shows the usefulness of dengue-3- and dengue-4-specific phage-displayed antibody fragments as tools for viral detection and serotyping in sera from infected individuals. C6/36 HT cells were inoculated with acute-phase sera from patients, and supernatants were collected daily and analyzed by ELISA using phage-displayed antibody fragments as serotype-specific detector reagents. Serotyping of most samples was possible as early as two to three days postinoculation. Results were comparable with those obtained by indirect immunofluorescence assay but were obtained in a shorter period of time (<1 week). Phage-displayed antibody fragments were better tools for diagnosis and serotyping than their soluble counterparts. Our approach combines the advantages of viral isolation and ELISA techniques. These results could be the basis for the development of a high-throughput method for identifying dengue virus serotypes, which is crucial for the management and control of the disease.

Higher temperature and urbanization affect the spatial patterns of dengue fever transmission in subtropical Taiwan

Our study conducted spatial analysis to examine how temperature and other environmental factors might affect dengue fever distributions, and to forecast areas with potential risk for dengue fever endemics with predicted climatic change in Taiwan. Geographic information system (GIS) was used to demonstrate the spatial patterns of all studied variables across 356 townships. Relationships between cumulative incidence of dengue fever, climatic and non-climatic factors were explored. Numbers of months with average temperature higher than 18 degrees C per year and degree of urbanization were found to be associated with increasing risk of dengue fever incidence at township level. With every 1 degrees C increase of monthly average temperature, the total population at risk for dengue fever transmission would increase by 1.95 times (from 3,966,173 to 7,748,267). A highly-suggested warmer trend, with a statistical model, across the Taiwan Island is predicted to result in a sizable increase in population and geographical areas at higher risk for dengue fever epidemics.

Global spread and persistence of dengue

Dengue is a spectrum of disease caused by four serotypes of the most prevalent arthropod-borne virus affecting humans today, and its incidence has increased dramatically in the past 50 years. Due in part to population growth and uncontrolled urbanization in tropical and subtropical countries, breeding sites for the mosquitoes that transmit dengue virus have proliferated, and successful vector control has proven problematic. Dengue viruses have evolved rapidly as they have spread worldwide, and genotypes associated with increased virulence have expanded from South and Southeast Asia into the Pacific and the Americas. This review explores the human, mosquito, and viral factors that contribute to the global spread and persistence of dengue, as well as the interaction between the three spheres, in the context of ecological and climate changes. What is known, as well as gaps in knowledge, is emphasized in light of future prospects for control and prevention of this pandemic disease.

What does dengue disease surveillance contribute to predicting and detecting outbreaks and describing trends?

OBJECTIVE

To review the evidence on the application of tools for dengue outbreak prediction/detection and trend monitoring in passive and active disease surveillance systems in order to develop recommendations for endemic countries and identify research needs.

METHOD

Systematic review of literature in the Cochrane Database of Systematic Reviews, PubMed, EMBASE, Lilacs, WHO library database, manual reference search and grey literature. Two reviewers independently applied pre-defined inclusion and exclusion criteria and assessed the level of evidence. Studies describing the outcome of dengue disease surveillance with respect to trend monitoring and outbreak prediction/detection based on empirical data were included.

RESULTS

Twenty-four studies (of 1804 references) met the eligibility criteria. Different indicators and their respective threshold values were identified as potential triggers for outbreak alerts through retrospective analysis of data from passive and/or active surveillance systems. Some indicators are potentially useful for predicting imminent outbreaks in the low transmission season and others for detecting outbreaks at an early stage. However, the information collected is mainly retrospective and often site-specific and appropriate levels of sensitivity and specificity of the outbreak indicators/triggers could not be determined. Retrospective and prospective virus surveillance studies were not conclusive regarding the question of whether a newly introduced serotype is an outbreak predictor, but contributed additional indicators for outbreak prediction/detection. Under-reporting was a major concern. Taking cost and feasibility issues into account, it remains an open question whether dengue surveillance should be passive (based on routine reporting) or active (based on more costly sentinel or other active population based surveillance systems). Adding active surveillance elements to a well-functioning passive surveillance system improves sensitivity; adding laboratory elements to the system improves specificity.

CONCLUSIONS

In view of the lack of evidence about the most feasible and sustainable surveillance system in a country context, countries could use a stepwise approach to locally adapt their passive routine surveillance system into an improved combined active/passive surveillance approach. Prospective studies are needed to better define the most appropriate dengue surveillance system and trigger for dengue emergency response.

Clinical isolates of dengue virus with distinctive susceptibility to nitric oxide radical induce differential gene responses in THP-1 cells

In the present study, 10 clinical isolates of dengue virus were selected according to their susceptibility to the inhibitory effect of nitric oxide radical, NO. Five of them are nitric oxide-susceptible viruses while the other five are nitric oxide-resistant viruses. These isolates were investigated to identify genetic factors that are responsible for the different phenotypes. Due to the evidence showing that NO suppresses DENV RNA polymerase activity, we, therefore, hypothesized that the RdRp domain of NS5 may responsible for NO inhibition. To answer this question, sequences of NS5 gene of NO-susceptible viruses and NO-resistant viruses were compared. We found that these two groups of viruses contain different amino acid sequence at position 621 to 646 in the active site of NS5. These data suggested that response to the inhibitory effect of nitric oxide radical may, at least in part, be regulated by NS5. The effect of these two different phenotypes of viruses on host cells was studied using cDNA array screening. The cDNA array analysis demonstrated that the nitric oxide-resistant group had a stronger influence on host cells since it induced changes in the expression of a greater number of genes than did the nitric oxide-susceptible group, 97 genes versus 71 genes, respectively. The NO-resistant virus also stimulated cytokines known to be virulent factors, such as IL 6, IL 8, RANTES, and the inflammatory factors. In conclusion, our data demonstrated that dengue viruses isolated from patients show genotypic and phenotypic differences which may correlate with virulence.

The health and economic impact of dengue in Latin America

In the last two decades, all countries in the tropical regions of Latin America have experienced marked increases in the incidence of both classic dengue and dengue hemorrhagic fever. Major risk factors for the occurrence of dengue in the region, as well as some regional peculiarities in its clinical expression, such as the extensive involvement of older age groups, have been defined. While little information exists on the economic impact of dengue in the region in terms of disease burden, the estimated loss associated with the disease is on the same order of magnitude as tuberculosis, sexually transmitted diseases (excluding HIV/AIDS), Chagas disease, leishmaniasis, or intestinal helminths. Therefore, similar priority should be given in the allocation of resources for dengue research and control. Data on cost-efficacy and cost-benefit analysis of dengue control programs in Latin America are scarce; however, the cost per DALY averted by control programs during endemic periods appears low, as compared to other mosquito-borne diseases like yellow fever, leishmaniasis, or malaria. Additionally, the cost-benefit ratio of the control programs has proven to be positive.

An integrated ecosystem approach for sustainable prevention and control of dengue in Central Havana

The authors developed and evaluated a comprehensive participatory ecosystem health approach for preventing the transmission of dengue, the most prevalent vector-borne disease in Cuba and the Latin America-Caribbean region. The integrated surveillance system central to this initiative encompassed three main subsystems (environmental; entomological; clinical-epidemiologic), relying on extensive community involvement. The study was conducted in Central Havana, Cuba. Indicators from each subsystem were selected and mapped using a GIS procedure providing instant visualization by city block in the municipality. To elucidate the factors affecting control and prevention efforts, perceived needs and risks, as well as knowledge, attitudes, and behaviors related to dengue, were assessed. Specific factors associated with the presence of mosquito breeding sites and risks of dengue were examined in a case-control study.

Community participation in Aedes aegypti control: a sociological perspective on five years of research in the health area ''26 de Julio'', Havana, Cuba

OBJECTIVE

Effective dengue prevention and Aedes aegypti control is a priority for the Cuban health authorities. To enhance effectiveness, strategies oriented towards a more active involvement of communities in control activities are being tested. This paper presents a sociological perspective on a pilot project conducted in the health area ''26 de Julio'' (La Havana) in 1999-2004.

METHODS

Instrumental case study based on an exhaustive content analysis of project documents and on observations of a sociologist.

RESULTS

The context and the pilot project are systematically described and an analysis of the evolution of the underlying concept of community participation is provided. The pilot experience was a dynamic process influenced by self-reflection of the research team, feedback from research partners and changes in the epidemiological context (provoked by two dengue outbreaks during the study period). Community participation evolved from being just one component in Aedes aegypti control directed by the health staff into a learning and empowering process for the people. This change in the concept of participation was reflected in different aspects of the pilot project such as the learning and evaluation processes.

CONCLUSION

Empirical evidence from 5 years of research in the particular context of Cuba showed that moves towards community-based Aedes aegypti control are feasible. However, in order to be successful, community-based dengue prevention should be a social learning process, implying a transfer of power and responsibilities to local people. Actions undertaken must be oriented towards creating local capabilities, strengthening existing structures and organizations and promoting group work for learning participation from participation itself.

HLA-A, -B, -C, and -DRB1 allele frequencies in Cuban individuals with antecedents of dengue 2 disease: Advantages of the Cuban population for HLA studies of dengue virus infection

Dengue virus infection has emerged as one of the most important arthropod-borne diseases. In some dengue-infected individual, the disease progresses to its severe, life-threatening form, dengue hemorrhagic fever (DHF). Host genetic factors may be relevant and predispose some individuals to the severe dengue disease. The unique history of dengue outbreaks in Cuba is extremely advantageous for genetic studies of dengue disease resistance or susceptibility. Consequently, samples collected from 120 healthy individuals that developed dengue fever (DF) and DHF during the 1997 dengue 2 outbreak in the Santiago de Cuba municipality were HLA genotyped using polymerase chain reaction-sequence-specific primers. Polymorphism at the human leukocyte antigen (HLA) class I loci was significantly associated with DHF disease susceptibility, but polymorphism in the HLA-DRB1 was associated with protection. Amino acid peptides present in the poly-protein of the dengue 2 Jamaica strain, which are able to bind to the HLA class I and class II allotypes associated with susceptibility to or protection against the dengue clinical disease, respectively, were predicted using the BIMAS and SYFPEITHI predictive algorithms of peptide/MHC interaction.

Ethnicity and difference in dengue virus-specific memory T cell responses in Cuban individuals

The different risk factors associated with dengue hemorrhagic fever pathogenesis needs yet additional clarification. The exceptional epidemiological circumstances in Cuba allow their evaluation in a well-defined situation. In the present study the memory T cell response of 80 Cuban donors previously infected with dengue-1 and dengue-2 during the 1977 and 1981 epidemics, and belonging to different ethnic groups, was examined. White people showed, in contrast to black people, stronger and remarkably cross-reactive dengue virus-specific memory CD4(+) T lymphocyte proliferation and interferon-gamma release. The observed variation in T cell response according to ethnicity could be related to the immunopathogenesis of dengue hemorrhagic fever, and may partially explain the epidemiological evidence that black individuals are at lower risk for the most severe dengue clinical course compared with white individuals.

Neutralizing antibodies after infection with dengue 1 virus

Severity of disease is markedly increased when infection with dengue virus type 2 (DENV-2) follows infection with DENV-1 at an interval of 20 years. Studies have shown that heterologous neutralizing antibody titers are inversely correlated with severity of a second infection. If this mechanism controlled disease severity in Cuba, heterotypic antibody titers should have declined over time. To determine whether phenotypic changes in dengue antibodies occur over time, we analyzed serum samples collected 4-8 and 20-22 years after DENV-1 infection. We found a significant increase in mean titer of homologous DENV-1 neutralizing antibodies and a significant decrease in heterologous antibodies to 1 of 2 genotypes of DENV-2 virus (the American genotype). Asian DENV-2 viruses were not neutralized during either interval; however, the American genotype underwent phenotypic changes in heterotypic viral neutralizing antibodies in the predicted direction. This finding may be related to the time-dependent changes in severity of disease found with secondary dengue infection.