Dengue Immunopathogenesis: A Crosstalk between Host and Viral Factors Leading to Disease: PART II - DENV Infection, Adaptive Immune Responses, and NS1 Pathogenesis

Severe disease is associated with serial infection with DENV of different serotypes. Thus, primary DENV infections normally cause asymptomatic infections, and secondary heterotypic infections with a new DENV serotype potentially increase the risks of developing severe disease. Despite many proposed hypotheses trying to explain it, the exact immunological mechanism leading to severe dengue disease is unknown. In turn, severe manifestations are believed to be a consequence of the combinations of many immunopathogenic mechanisms involving viral and host factors leading to increased pathogenesis and disease. Of these mechanisms, the adaptive immune response has been proposed to play a critical role in the development of severe dengue manifestations. This includes the effect of non-neutralizing but enhancing antibodies produced during primary infections, which results in enhanced-DENV infection of Fc-γ-receptor-expressing cells (e.g. monocytes and macrophages) during DENV heterotypic exposure in a phenomenon called antibody-dependent enhancement (ADE); the increased activation of memory T cells during secondary infections, which has low affinity for the current infecting serotype and high affinity for a past infection with a different serotype known as the original antigenic sin; the unbalanced production of pro-inflammatory cytokines that have a direct effect on vascular endothelial cells resulting in plasma leak in a phenomenon known as cytokine storm; and the excessive activation of the complement system that causes exacerbated inflammatory responses, increasing disease severity. In addition to the adaptive immune responses, a secreted viral factor known as the nonstructural protein 1 (NS1) has been recently proposed as the missing corner piece of the DENV pathogenesis influencing disease. This Part II of the chapter will discuss the interplay between the distinct host adaptive immune responses and viral factors that together contribute to the development of DENV pathogenesis and severe disease.

Novel Single Hematophagous Insect RNA Detection Method Supports Its Use as Sentinels to Survey Flaviviruses Circulation

Anthropogenic actions, including deforestation, disorganized urbanization, and globalization, contribute to emergence and reemergence of arboviruses worldwide, where Flavivirus is the most prevalent, and its continuous monitoring can help in preventive control strategies. Thus, the aim of this study was to detect flavivirus RNA in single hematophagous insects, which are used as sentinels. Total RNA was extracted from six Aedes aegypti stored since 2003 and from 100 Culicidae and collected through CDC trap in a public park of a Brazilian Northwest city of São Paulo State. Flavivirus was detected through RT/PCR targeting 230–250 bp of the RNA polymerase coding sequence (NS5). PCR amplicons were sequenced by Sanger method, used in comparative analysis over Basic Local Alignment Search Tool (BLAST) in GenBank, and subjected to Neighbor-Joining phylogenetic analyses. Efficiency of Flavivirus diagnosis was confirmed by detection of Dengue virus serotype 2 in Ae. aegypti. From the 100 collected insects, 19 were positive for Culex flavivirus (CxFV). NS5 partial sequence phylogenetic analysis clustered all CxFV in one branch separated from vertebrate flaviviruses, being applicable to the identification of Flavivirus species. The dipteran RNA extraction methodology described in this work supports detection of flaviviruses in single insects maintained in 80% ethanol, which can be used to constant arbovirus surveillance.

Dengue Virus and the Relationship with MicroRNAs

Dengue is an acute febrile disease caused by a virus of the genus Flavivirus, family Flaviviridae, endemic in tropical regions of the globe. The agent is a virus with single-stranded RNA, classified into four distinct dengue virus (DENV) serotypes: DENV-1, DENV-2, DENV-3, and DENV-4. The host’s innate and adaptive immune responses play an essential role in determining the natural history of viral infections, especially in dengue. In this context, it has observed in recent years that the presence of RNA interference (RNAi) in viral infection processes is increasing, as well as immune defense. The context microRNAs (miRNAs) go for stood out, as their presence during viral infection, both in the replication of the virus and in the defense against these infections, becomes increasingly noticeable, therefore, making it increasingly necessary to better understand the role of these small RNAs within viral infection by DENV and what their consequences are in aggravating the consequences of patients affected by this disease.

Situation of Dengue after the Phenomenon of the Coastal El Niño

Coastal El Niño is a weather phenomenon that is caused by abnormal warming (above 0.4°C) of the Pacific Ocean waters near the coasts of Ecuador and Peru, and it can even reach the central and southern Peruvian coast. As a result of the climatic phenomenon, the Aedes aegypti vector (which in turn is a vector of chikungunya and Zika fever) had been quickly installed in 448 districts of Peru, and emergency was declared in 10 regions, which reported 231,874 victims; 1,129,013 affected and 143 dead. It is necessary to know this, because the direct impact of the weather phenomena contributes to the dengue vector conditioning, facilitating its dissemination with ease. The geographical and climatic conditions of the cities most affected by the El Niño Costero phenomenon turned them into zones of epidemics; in these places, there is an important population growth, from urbanization to sectorization in young towns and urban slums, where in many there is no basic infrastructure and water supply is insufficient, which requires temporary water storage, as well as high temperatures, migratory movement, and beaches with influx of people, which make not only dengue proliferate but also other arbovirosis such as chikungunya.

Dengue Immunopathogenesis: A Crosstalk between Host and Viral Factors Leading to Disease: Part I - Dengue Virus Tropism, Host Innate Immune Responses, and Subversion of Antiviral Responses

Dengue is the most prevalent emerging mosquito-borne viral disease, affecting more than 40% of the human population worldwide. Many symptomatic dengue virus (DENV) infections result in a relatively benign disease course known as dengue fever (DF). However, a small proportion of patients develop severe clinical manifestations, englobed in two main categories known as dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Secondary infection with any of the four dengue virus serotypes (DENV1, -2, -3, and -4) is a risk factor to develop severe forms of dengue disease. DSS is primarily characterized by sudden and abrupt endothelial dysfunction, resulting in vascular leak and organ impairment, which may progress to hypovolemic shock and death. Severe DENV disease (DHF/DSS) is thought to follow a complex relationship between distinct immunopathogenic processes involving host and viral factors, such as the serotype cross-reactive antibody-dependent enhancement (ADE), the activation of T cells and complement pathways, the phenomenon of the cytokine storm, and the newly described viral toxin activity of the nonstructural protein 1 (NS1), which together play critical roles in inducing vascular leak and virus pathogenesis. In this chapter that is divided in two parts, we will outline the recent advances in our understanding of DENV pathogenesis, highlighting key viral-host interactions and discussing how these interactions may contribute to DENV immunopathology and the development of vascular leak, a hallmark of severe dengue. Part I will address the general features of the DENV complex, including the virus structure and genome, epidemiology, and clinical outcomes, followed by an updated review of the literature describing the host innate immune strategies as well as the viral mechanisms acting against and in favor of the DENV replication cycle and infection.

Lessons Learned and Recent Advances in Dengue Research

Dengue is the most important arbovirus, many research have contributed to the diagnosis, management, prevention and control of this disease, which will be described in this chapter, for example: the importance of serotypes and genotypes for the development of the disease, the relationship of the viral load between symptomatic and asymptomatic people, the influence of antibodies on the development of the disease, co-infections with microorganisms and chronic diseases, possible reservoirs, the diagnostic assays, cross-reactions in the diagnosis, the influence of climate change on the disease and the vector, mechanisms of transmission of the disease, new drugs and plant extracts with antiviral activity, the dengue vaccine, the results of immunizations, etc. This information gives a concrete idea of the advances and challenges against this disease.

Dengue Fever: An Overview

Dengue fever is a disease caused by a family of viruses transmitted by mosquitoes. Dengue virus (DENV), a member of the Flaviviridae family, causes the most widespread mosquito-borne viral infection in humans around the world today. Dengue can affect anyone but tends to be more severe in people with compromised immune systems. Dengue hemorrhagic fever is a more severe form of a viral illness. Symptoms include headache, fever, rash, and evidence of bleeding (hemorrhage) in the body. This form of dengue fever can be life-threatening and can progress to the most severe form of the illness, dengue shock syndrome. This chapter reviews the etiology, epidemiology, diagnosis, pathophysiology, transmissions, manifestations, diagnosis, treatment, and prevention of dengue.

Phage Display as a Strategy to Obtain Anti-flavivirus Monoclonal Antibodies

Arbovirus of the Flaviviridae family represents an issue worldwide, particularly because it can lead to serious illness and death in some countries. There is still a great complexity in obtaining effective therapies and specific and sensitive diagnostic tests, due to the high antigenic similarity between them. This similarity may account for antibodies cross reactivity which has positive and negative consequences for the course of infectious diseases. Among dengue virus (DENV) serotype infections, the cross-reactivity can increase virus replication and the risk of a severe disease by a mechanism known as an antibody-dependent enhancement (ADE). The search for serological biomarkers through monoclonal antibodies (MAbs) that identify unique viral regions can assist in the differential detection, whereas the development of recombinant antibodies with a neutralizing potential can lead to the establishment of efficacious treatments. The Phage Display methodology emerged as one of the main alternatives for the selection of human MAbs with high affinity for a specific target. Therefore, this technology can be a faster alternative for the development of specific diagnostic platforms and efficient and safe treatments for flavivirus infections. In this context, we propose for this chapter a discussion about Phage Display as a strategy to obtain MAbs for DENV and other flaviviruses.