The decline of dengue in the Americas in 2017: discussion of multiple hypotheses.

OBJECTIVE: Since the 1980s, dengue incidence has increased 30-fold. However, in 2017, there was a noticeable reduction in reported dengue incidence cases within the Americas, including severe and fatal cases. Understanding the mechanism underlying dengue's incidence and decline in the Americas is vital for public health planning. We aimed to provide plausible explanations for the decline in 2017. METHODS: An expert panel of representatives from scientific and academic institutions, Ministry of Health officials from Latin America and PAHO/WHO staff met in October 2017 to propose hypotheses. The meeting employed six moderated plenary discussions in which participants reviewed epidemiological evidence, suggested explanatory hypotheses, offered their expert opinions on each and developed a consensus. RESULTS: The expert group established that in 2017, there was a generalised decreased incidence, severity and number of deaths due to dengue in the Americas, accompanied by a reduction in reported cases of both Zika and chikungunya virus infections, with no change in distribution among age groups affected. This decline was determined to be unlikely due to changes in epidemiological surveillance systems, as similar designs of surveillance systems exist across the region. Although sudden surveillance disruption is possible at a country or regional level, it is unlikely to occur in all countries simultaneously. Retrospective modelling with epidemiological, immunological and entomological information is needed. Host or immunological factors may have influenced the decline in dengue cases at the population level through immunity; however, herd protection requires additional evidence. Uncertainty remains regarding the effect on the outcome of sequential infections of different dengue virus (DENV) types and Zika virus (ZIKV), and vice versa. Future studies were recommended that examine the epidemiological effect of prior DENV infection on Zika incidence and severity, the epidemiological effect of prior Zika virus infection on dengue incidence and severity, immune correlates based on new-generation ELISA assays, and impact of prior DENV/other arbovirus infection on ZIKV immune response in relation to number of infections and the duration of antibodies in relation to interval of protection. Follow-up studies should also investigate whether increased vector control intensification activities contributed to the decline in transmission of one or more of these arboviruses. Additionally, proposed studies should focus on the potential role of vector competence when simultaneously exposed to various arboviruses, and on entomological surveillance and its impact on circulating vector species, with a goal of applying specific measures that mitigate seasonal occurrence or outbreaks. CONCLUSIONS: Multifactorial events may have accounted for the decline in dengue seen in 2017. Differing elements might explain the reduction in dengue including elements of immunity, increased vector control, and even vector and\or viruses changes or adaptations. Most of the results of this expert consensus group meeting are hypothetical and based on limited evidence. Further studies are needed.

OBJECTIF: Depuis les années 1980, l'incidence de la dengue a été multipliée par 30. Cependant, en 2017, il y a eu une réduction notable du nombre de cas d'incidence de dengue rapportés dans les Amériques. Nous voulions fournir des explications plausibles à la baisse en 2017. MÉTHODES: Un groupe d'experts constitué de représentants d'institutions scientifiques et académiques, d'officiels des Ministères de la Santé d'Amérique Latine et de membres du personnel de l'OPS/OMS s'est réuni en octobre 2017 pour proposer et évaluer des hypothèses. RÉSULTATS: En 2017, il y a eu une baisse généralisée de l'incidence, de la sévérité et du nombre de décès dus à la dengue dans les Amériques, accompagnée d'une réduction des cas rapportés d'infections par le virus Zika et par le virus du chikungunya, sans modification dans la répartition entre les groupes d'âge affectés. Il a été déterminé que ce déclin était peu probablement dû aux changements dans les systèmes de surveillance épidémiologique, étant donné que des systèmes de surveillance similaires existaient dans toute la région. Bien que des perturbations soudaines dans la surveillance soient possibles au niveau national ou régional, il est peu probable que cela se produise simultanément dans tous les pays. Une modélisation rétrospective avec des informations épidémiologiques, immunologiques et entomologiques est nécessaire. Des facteurs liés à l'hôte ou immunologiques peuvent avoir influencé le déclin des cas de dengue au niveau de la population par le biais de l'immunité; cependant, l'évidence d'une protection conférée par l'effet du troupeau nécessite des données supplémentaires. Une incertitude subsiste quant à l'effet sur le résultat des infections séquentielles de différents types du virus de la dengue (DENV) et du virus Zika (ZIKV), et vice-versa. Les études à venir devraient examiner (1) l'effet épidémiologique d'une infection antérieure par le DENV sur l'incidence et la sévérité du virus Zika, (2) l'effet épidémiologique d'une infection antérieure par le virus Zika sur l'incidence et la sévérité de la dengue, (3) les corrélats immunitaires basés sur des tests ELISA de nouvelle génération, (4) l' impact d'une infection antérieure à DENV/autres arbovirus sur la réponse immunitaire au ZIKV en fonction du nombre d'infections et de la durée des anticorps en fonction de l'intervalle de protection, (5) si des activités d'intensification de la lutte antivectorielle ont contribué à la diminution de la transmission d'un ou plusieurs de ces arbovirus, (6) le rôle potentiel de la compétence vectorielle lorsqu'ils sont exposés simultanément à différents arbovirus, (7) la surveillance entomologique et son impact sur la circulation d'espèces de vecteurs, dans le but d'appliquer des mesures spécifiques qui réduisent l'occurrence saisonnière d'épidémies. CONCLUSIONS: Des événements multifactoriels pourraient expliquer le déclin observé de la dengue en 2017. La plupart des résultats de cette réunion du groupe de consensus d'experts sont hypothétiques, reposent sur des données limitées et requièrent des investigations supplémentaires.

WHO dengue case classification 2009 and its usefulness in practice: an expert consensus in the Americas.

INTRODUCTION: In 2009, the new World Health Organization (WHO) dengue case classification - dengue/severe dengue (D/SD) - was introduced, replacing the 1997 WHO dengue case classification: dengue fever/dengue haemorrhagic fever/dengue shock syndrome (DF/DHF/DSS). METHODS: A 2-day expert consensus meeting in La Habana/Cuba aimed to (1) share the experiences from Pan American Health Organization (PAHO) member states when applying D/SD, (2) present national and local data using D/SD, and (3) agree with the presented evidence on a list of recommendations for or against the use of D/SD for PAHO, and also globally. RESULTS: Eight key questions were discussed, concluding: (1) D/SD is useful describing disease progression because it considers the dynamic nature of the disease, (2) D/SD helps defining dengue cases correctly for clinical studies, because it defines more precisely disease severity and allows evaluating dynamically the progression of cases, (3) D/SD describes correctly all clinical forms of severe dengue. Further standards need to be developed regionally, especially related to severe organ involvement, (4) D/SD allows for pathophysiological research identifying - in a sequential manner - the clinical manifestations of dengue related to pathophysiological events, (5) the warning signs help identifying early cases at risk of shock (children and adults), pathophysiology of the warning signs deserves further studies, (6) D/SD helps treating individual dengue cases and also the reorganization of health-care services for outbreak management, (7) D/SD helps diagnosing dengue, in presumptive diagnosis and follow-up of the disease, because of its high sensitivity and high negative predictive value (NPV), and (8) there is currently no update of the International Disease Classification10 (ICD10) to include the new classification of dengue (D/SD); therefore, there are not enough experiences of epidemiological reporting. Once D/SD has been implemented in epidemiological surveillance, D/SD allows to (1) identify severity of dengue cases in real time, for any decision-making on actions, (2) measure and compare morbidity and mortality in countries, and also globally, and (3) trigger contingency plans early, not only based on the number of reported cases but also on the reported severity of cases. CONCLUSION: The expert panel recommends to (1) update ICD10, (2) include D/SD in country epidemiological reports, and (3) implement studies improving sensitivity/specificity of the dengue case definition.

La estrategia para la prevención y el control integrado del dengue en Mesoamérica / Integrated prevention and control strategy for dengue in Mesoamerica

El dengue en las Américas es un problema de salud pública en ascenso. Las estrategias de control han sido poco efectivas al sustentarse en el uso intensivo de insecticidas y la poca participación de la comunidad. La Iniciativa Mesoamericana para la Prevención y el Control Integrado del Dengue integra los trabajos generados por la Estrategia de Gestión Integrada de la Organización Panamericana para la Salud (OPS) y la estrategia de estratificación de riesgos diseñada para los países de la región mesoamericana. El objetivo es reducir progresivamente la incidencia de dengue hasta un 50% de los casos en cinco años. En este documento se describen los elementos para la estratificación de riesgo, las actividades de prevención y control escalonadas en intensidad y frecuencia y los indicadores de seguimiento para el logro de los objetivos. Frente a la dispersión del problema se propone concentración de esfuerzos de control en las áreas de mayor riesgo; ante la rapidez de la transmisión se propone la oportunidad en la detección de casos; contra la expansión de los criaderos se propone la focalización de las acciones sobre los criaderos más productivos; y ante la severidad de la infección se propone un manejo clínico adecuado. Dicha estrategia se diseñó con los representantes nacionales de los programas de control para crear planes maestros que proporcionaran las bases para la prevención y el control integrado del dengue en la región mesoamericana.

Dengue in the Americas is a public health problem in ascent. The control strategies have not been effective when sustained in the intensive use of insecticides and poor community participation. The Mesoamerican Initiative for the Prevention and the Integrated Control of Dengue synthesizes the works generated by the Integrated Strategy of the Pan-American Health Organization (PAHO) and the risks stratification strategy designed by the countries of the Mesoamerican region. The objective is to progressively reduce the incidence of dengue cases until a 50% reduction is reached over a five years period. This document describes the elements for the risk stratification, the activities for prevention and control organized by levels of intensity and frequency and the indicators used to pursuit the objectives. To face the dispersion of the problem a concentration of efforts for control in the areas of greater risk is presented; the opportunity in the detection of cases is highlighted to tackle the fast dissemination of the infection; focus on the most productive breeding sites is proposed to battle against the vast dissemination of the breeding sites; and the severity of the infection must be addressed by capable clinical human resources. This strategy was designed along with the national representatives of the control programs to create master plans that provided the basis for the integrated prevention and control of dengue in the Mesoamerican region.