Vascular dysfunction in hemorrhagic viral fevers: opportunities for organotypic modeling

The hemorrhagic fever viruses (HFVs) cause severe or fatal infections in humans. Named after their common symptom hemorrhage, these viruses induce significant vascular dysfunction by affecting endothelial cells, altering immunity, and disrupting the clotting system. Despite advances in treatments, such as cytokine blocking therapies, disease modifying treatment for this class of pathogen remains elusive. Improved understanding of the pathogenesis of these infections could provide new avenues to treatment. While animal models and traditional 2D cell cultures have contributed insight into the mechanisms by which these pathogens affect the vasculature, these models fall short in replicatingin vivohuman vascular dynamics. The emergence of microphysiological systems (MPSs) offers promising avenues for modeling these complex interactions. These MPS or 'organ-on-chip' models present opportunities to better mimic human vascular responses and thus aid in treatment development. In this review, we explore the impact of HFV on the vasculature by causing endothelial dysfunction, blood clotting irregularities, and immune dysregulation. We highlight how existing MPS have elucidated features of HFV pathogenesis as well as discuss existing knowledge gaps and the challenges in modeling these interactions using MPS. Understanding the intricate mechanisms of vascular dysfunction caused by HFV is crucial in developing therapies not only for these infections, but also for other vasculotropic conditions like sepsis.

Correlation of Dengue Warning Signs during Febrile Phase with Rotational Thromboelastometry, Cortisol and Feritin

Dengue mortality remains high despite monitoring against warning signs (WS). The associations of WS at febrile phase (FP) and hemorrhage at defervescence with the levels and kinetics of ROTEM, platelet count, cortisol, and ferritin were analyzed. Patients with confirmed dengue serology and WS in two centers were screened (n = 275) and 62 eligible patients were recruited prospectively over 9 months. “Vomiting” was the commonest WS (62.9%), with shortened clotting time (CT) INTEM (p = 0.01). “Hematocrit increase” showed significant prolonged CT INTEM, EXTEM, and FIBTEM (p < 0.05). “Platelet decrease” showed reduced platelet function and reduced clot amplitude at 10 min (A10) and maximum clot firmness (MCF) in INTEM and EXTEM (p < 0.001). The kinetics were reduced in platelet count, CT EXTEM, and cortisol (p < 0.05) but increased in CT INTEM (p = 0.03). At FP, “vomiting”, “hematocrit increase”, and “platelet decrease” demonstrated impaired CT, clot strengths A10/MCF and platelet functions. Majority (60/62, 96.7%) had non-severe outcomes, consistent with increase in cortisol kinetics. In conclusion, “vomiting”, “hematocrit increase” and “platelet decrease” at FP correlated with ROTEM. No conclusion could be made further regarding ferritin and cortisol. Larger study is required to study “hematocrit increase” with ROTEM as a potential marker for hemorrhage.

Use of Animal Models in Studying Roles of Antibodies and Their Secretion Cells in Dengue Vaccine Development

The cardinal feature of adaptive immunity is its ability to form memory responses that can be rapidly recalled to contain pathogens upon reencountering. Conferring a robust memory immune response to an infection is a key feature for a successful vaccination program. The plasmablasts are cells that not only can secret non-neutralizing antibodies but also can secrete the specific antibodies essential to neutralize and inactivate the invading pathogens. Dengue has been recognized as one of the most important vector-borne human viral diseases globally. Currently, supportive care with vigilant monitoring is the standard practice since there is as yet no approved therapeutic modality to treat dengue. Even though the approved vaccine has become available, its low efficacy with the potential to cause harm is the major hurdle to promote the widespread usage of the vaccine. Despite the decades of research on dengue, the major challenge in dengue vaccine development is the absence of suitable experimental animal models that reflect the pathological features and clinical symptoms, as seen in humans. Dengue is transmitted by the bite of mosquitoes carrying infectious dengue virus (DENV), which has four distinct serotypes. Recently, cases resulting from unconventional transmission routes, such as blood transfusion, organs as well as stem cells and bone marrow transplantations, and mother-to-infant vertical transmission, have been reported, suggesting an alternate route of DENV transmission exists in nature. This review discusses issues and challenges needing to be resolved to develop an effective dengue vaccine. Development of a robust and reliable dengue animal model that can reflect not only dynamic human clinical symptoms but also can answer around why preexisting neutralizing antibodies do not confer protection upon re-infection and immune protection marker for dengue vaccine efficacy evaluation.

Coronavirus Disease of 2019: a Mimicker of Dengue Infection?

At the beginning of 2020, the national health system and medical communities are faced with unprecedented public health challenges. A novel strain of coronavirus, later identified as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread globally, marking another pandemic of coronaviruses. This viral disease is responsible for devastating pneumonia, named coronavirus disease of 2019 (COVID-19), and projected to persist until the end of the year. In tropical countries, however, concerns arise regarding the similarities of COVID-19 with other infectious diseases due to the same chief complaint, which is fever. One of the infectious disease of a primary concern is dengue infection, which its peak season is approaching. Others report that there are cases of serological cross-reaction of COVID-19 and dengue infection. In this comprehensive review, we underscore the importance of knowing similar clinical presentations of both diseases and emphasize why excluding COVID-19 in the differentials in the setting of a pandemic is imprudent.

Altered Platelet Fatty Acids in Dengue Cases by Gas Chromatography-Mass Spectrometry Analysis

BACKGROUND

The role of dengue virus in altering the functional properties of platelets remains poorly understood. Few studies have observed that changes in fatty acids are found to have an effect on platelet activation and aggregation. Also, platelet fatty acids have not been extensively studied in dengue so far. So, we aimed to study the fatty acids of platelet membranes in patients with dengue.

METHODS

Gas chromatography-mass spectrometry (GC-MS) method was used to analyze fatty acids in the lipid extracts of platelets isolated from the study participants.

RESULTS

GC-MS analysis of platelet lipids identified and quantified nearly 23 unique lipid molecules on platelet membrane. We observed significant alterations with some of the fatty acids in patients with dengue compared to controls. Within dengue cases, increase in unsaturated fatty acids in severe dengue was observed compared to non-severe dengue. From baseline to defervescence, no difference in fatty acids was observed in dengue platelets. This indicates that in dengue, platelet physiology remains altered even after the febrile phase.

CONCLUSION

To the best of our knowledge, this is the first study characterizing the differential expression of platelet fatty acids in dengue infection. However, further studies are warranted to expound the underlying cause for thrombocytopenia and platelet dysfunction in dengue.

Human platelet antigens in disease

Platelets have various functions and participate in primary hemostasis, inflammation, and immune responses. Human platelet antigens (HPAs) are alloantigens expressed on the platelet membrane. Each HPA represent one of six platelet glycoproteins GPIIb, GPIIIa, GPIa, GPIbα, GPIbβ, and CD109, and six biallelic systems are grouped. A single nucleotide polymorphism (SNP) in the gene sequence causes a single amino acid substitution of relevant platelet glycoprotein with the exception of HPA-14bw. High-throughput next-generation sequencing-based method has been developed, which enable accurately identification of HPA polymorphisms. The roles of HPA in disease were reviewed. HPAs mediate platelet-microorganism and platelet-malignant cell interactions, and they also participate in pathogenesis of hemorrhagic fever with renal syndrome and infective endocarditis. The exploration of HPA polymorphisms in association with disease susceptibility of individuals will benefit prevention or management of disease.

Anti-dengue virus nonstructural protein 1 antibodies contribute to platelet phagocytosis by macrophages

Thrombocytopenia is an important clinical manifestation of dengue disease. The hypotheses concerning the pathogenesis of thrombocytopenia include decreased production and increased destruction or consumption of platelets. We previously suggested a mechanism of molecular mimicry in which antibodies (Abs) directed against dengue virus (DENV) nonstructural protein 1 (NS1) cross-react with platelets. Furthermore, several lines of evidence show activation of endothelial cells (ECs) and macrophages are related to dengue disease severity. Previous studies also suggested that Ab-opsonised platelets facilitate the engulfment of platelets by macrophages. Here we show that TNF-α-activated ECs upregulate adhesion molecule expression to enhance the binding of platelets and macrophages and lead to anti-DENV NS1 Ab-mediated platelet phagocytosis. We further demonstrate that the interaction between macrophages and TNF-α-activated ECs requires binding of FcγR with the Fc region of platelet-bound anti-DENV NS1 Abs. Importantly, the binding of anti-DENV NS1 Abs to platelets did not interfere with platelet adhesion to ECs. The adhesion molecules ICAM-1 and β3 integrin expressed on ECs as well as the FcγR expressed on macrophages were critical in anti-DENV NS1 Ab-mediated platelet phagocytosis on activated ECs. Moreover, anti-DENV NS1 Abs dramatically enhanced platelet engulfment by macrophages in a murine model of DENV infection. Our study provides evidence for a novel role for anti-DENV NS1 Abs in the pathogenesis of thrombocytopenia in dengue disease by enhancing platelet phagocytosis by macrophages.

Thrombocytopenia in Dengue: Interrelationship between Virus and the Imbalance between Coagulation and Fibrinolysis and Inflammatory Mediators

Dengue is an infectious disease caused by dengue virus (DENV). In general, dengue is a self-limiting acute febrile illness followed by a phase of critical defervescence, in which patients may improve or progress to a severe form. Severe illness is characterized by hemodynamic disturbances, increased vascular permeability, hypovolemia, hypotension, and shock. Thrombocytopenia and platelet dysfunction are common in both cases and are related to the clinical outcome. Different mechanisms have been hypothesized to explain DENV-associated thrombocytopenia, including the suppression of bone marrow and the peripheral destruction of platelets. Studies have shown DENV-infected hematopoietic progenitors or bone marrow stromal cells. Moreover, anti-platelet antibodies would be involved in peripheral platelet destruction as platelets interact with endothelial cells, immune cells, and/or DENV. It is not yet clear whether platelets play a role in the viral spread. Here, we focus on the mechanisms of thrombocytopenia and platelet dysfunction in DENV infection. Because platelets participate in the inflammatory and immune response by promoting cytokine, chemokine, and inflammatory mediator secretion, their relevance as "immune-like effector cells" will be discussed. Finally, an implication for platelets in plasma leakage will be also regarded, as thrombocytopenia is associated with clinical outcome and higher mortality.

Hemostatic derangement in dengue hemorrhagic fever

Dengue hemorrhagic fever (DHF) is a more severe manifestation of dengue virus infection. Patients with DHF exhibit abnormal hematological indices, including high hematocrit, low white blood cells, low neutrophils, high lymphocytes, increased atypical lymphocytes, low platelets, slightly prolonged activated partial thromboplastin time, prothrombin time, and thrombin time. Abnormal platelet functions manifest as impaired platelet aggregation to ADP, and concurrent increases in plasma thromboglobulin and platelet factor 4 levels are also seen. Variable reductions in the activities of coagulation factors including prothrombin, V, VII, VIII, IX, and X may be present. The plasma level of antithrombin is typically normal, but protein C and protein S are modestly reduced. Within the fibrinolytic system, slightly increased levels of tissue-plasminogen activator accompanied by slightly increased plasminogen activator inhibitor-1 and decreased thrombin activatable fibrinolysis inhibitor have been demonstrated. These derangements are prominent in patients with DHF grades III and IV, collectively known as dengue shock syndrome. Moreover, patients with excessive depletion of intravascular volume from plasma leakage and/or massive bleeding from endothelial dysfunction, thrombocytopenia, platelet dysfunction, and coagulopathy may exhibit shock, prolonged shock and repeated shock. DIC is also commonly found in these complicated patients. However, most patients recover spontaneously with normalization of abnormal laboratory profiles during the convalescent stage or within one to two weeks after defervescence.

Aedes mosquito saliva modulates Rift Valley fever virus pathogenicity

Background

Rift Valley fever (RVF) is a severe mosquito-borne disease affecting humans and domestic ruminants. Mosquito saliva contains compounds that counteract the hemostatic, inflammatory, and immune responses of the host. Modulation of these defensive responses may facilitate virus infection. Indeed, Aedes mosquito saliva played a crucial role in the vector's capacity to effectively transfer arboviruses such as the Cache Valley and West Nile viruses. The role of mosquito saliva in the transmission of Rift Valley fever virus (RVFV) has not been investigated.

Objective

Using a murine model, we explored the potential for mosquitoes to impact the course of RVF disease by determining whether differences in pathogenesis occurred in the presence or absence of mosquito saliva and salivary gland extract.

Methods

C57BL/6NRJ male mice were infected with the ZH548 strain of RVFV via intraperitoneal or intradermal route, or via bites from RVFV-exposed mosquitoes. The virus titers in mosquitoes and mouse organs were determined by plaque assays.

Findings

After intraperitoneal injection, RVFV infection primarily resulted in liver damage. In contrast, RVFV infection via intradermal injection caused both liver and neurological symptoms and this route best mimicked the natural infection by mosquitoes. Co-injections of RVFV with salivary gland extract or saliva via intradermal route increased the mortality rates of mice, as well as the virus titers measured in several organs and in the blood. Furthermore, the blood cell counts of infected mice were altered compared to those of uninfected mice.

Interpretation

Different routes of infection determine the pattern in which the virus spreads and the organs it targets. Aedes saliva significantly increases the pathogenicity of RVFV.

Rift Valley fever is an endemic and epidemic zoonosis in Africa and the Arabic Peninsula. In humans, in the most severe cases the viral infection causes fulminant hepatitis associated with haemorrhagic fever, permanent blindness or severe encephalitis. Despite the importance of vector transmission in the spread of arboviruses, few studies on the physiopathology of viral infection have considered the role of the arthropod in the efficiency of viral infection. Moreover, the route of virus inoculation and the presence of the vector's saliva can potentially affect virus pathogenicity. Our results show that saliva from Aedes mosquitoes increases Rift Valley fever pathogenicity. Importantly, our study also revealed that RVFV transmitted via mosquito bites spread differently than virus inoculated by other routes. These observations may have interesting repercussions given the role mosquitoes were shown to play in the transmission of RVFV in humans during the last outbreak of the disease in Saudi Arabia. Identification of salivary proteins able to increase RVFV virulence may pave the way to new approaches to prevent or cure the disease.

The importance of hematopoietic progenitor cells in dengue

Scientific investigations designed to better understand and assess the distinguishing clinical characteristics pave the way to a successful treatment for a disease. Since the peripheral blood is obtained easily, the most frequent type of investigation performed on infectious agents focuses on the hematological components of blood drawn from patients. Bone marrow aspirates, although somewhat more difficult to obtain, should be evaluated more frequently because they provide additional information, giving us a glimpse into the development of the disease. Understanding the distinct and unique changes in hematological components of the bone marrow induced by a particular pathogen or corresponding to a specific illness may be a valuable asset for the diagnosis and prognosis of disease. A good example of a pathogen that could be better evaluated with greater knowledge of the bone marrow is dengue, one of the most important public vector-borne human diseases. Owing to the multitude of clinical manifestations and the dynamic alterations of various blood components over time, this disease is one of the most difficult to prevent and treat in humans. Although large amounts of data have been generated in the literature, there remains a large gap between this information and its relevance for the purpose of patient care. While evaluating the cellular components in the circulated blood from ill patients provides us with valuable information about the pathogenesis of various pathogens, there are other players participating in the progression to disease. The goal of this review is to emphasize the importance of bone marrow hematopoietic progenitor cells in disease and to inspire other researchers to incorporate them into their investigations on dengue pathogenesis. It is anticipated that the knowledge derived from these investigations not only elicit original concepts on the pathogenesis of dengue but also foster a new way of thinking in terms of vaccine or therapeutic development to prevent and treat dengue.

Role of CD61+ cells in thrombocytopenia of dengue patients

Although hematological disorders with salient features of thrombocytopenia have been well documented in dengue patients, the role of CD61-expressing platelets and the megakaryocytic cell lineage in the pathogenesis of dengue virus (DENV) infection remains largely unexplored. A prospective observational study was performed using blood samples and PBMCs from dengue-confirmed patients, as well as from rhesus monkeys (RM) experimentally infected with DENV. Immunohistochemical staining and FACS techniques were applied to evaluate the frequencies of CD61(+) cells that contained DENV antigen. Highly enriched population of CD61(+) cells was also isolated from acute DENV-infected RM and assayed for DENV RNA by quantitative RT-PCR. Results revealed that DENV antigen was found in small vesicles of varying size, and more frequently in anucleated cells associated with platelets in dengue patients. The DENV antigen-containing cells were CD61(+) and appeared to share characteristics of megakaryocytes. Kinetic profiles of CD61(+) cells from DENV-infected RM revealed a transient increase in CD61(+)CD62P(+) cells early after DENV infection. DENV RNA in a highly enriched population of CD61(+) cells from the infected RM was observed during acute stage. Our results indicate that virus containing CD61(+) cells may be directly linked to the platelet dysfunction and low platelet count characteristics of dengue patients.

Management of severe refractory thrombocytopenia in dengue hemorrhagic fever with intravenous anti-D immune globulin

Dengue hemorrhagic fever (DHF) is a potentially lethal complication of dengue fever due to shock and/or bleeding. Bleeding in DHF is due to thrombocytopenia and/or coagulopathy. The authors present their experience of usage of intravenous anti-D in 5 children with DHF and severe refractory thrombocytopenia (<10,000/mm(3)). It was administered in a dose of 50 to 75 μg/kg. Mean platelet count was 6800/mm(3) before and 33,600, 44,600, and 79,000/mm(3) after intravenous anti-D administration at 24, 48, and 72 hours, respectively. Average drop in hemoglobin after administration of anti-D was 2.28 g/dL. Intravenous anti-D can possibly be a treatment option for refractory thrombocytopenia in DHF.

A re-evaluation of the mechanisms leading to dengue hemorrhagic fever

Viremia is one of the features of dengue virus infection among the flaviviruses. Dengue virus infection results in a spectrum of clinical symptoms, ranging from undifferentiated flu-like illness, mild dengue fever, to dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS), a life-threatening illness. Several mechanisms have been hypothesized based primarily on data collected from post-acute clinical phase to account for DHF/DSS. Lack of a suitable animal model for DHF/DSS has hindered progress in defining the etiology of DHF/DSS. Levels of circulating dengue virus have been well-correlated to severe dengue disease. However, the cell lineage(s) serving as a primary target for the source of viremia are largely unknown. Results from in vivo and in vitro pilot studies using molecular and more advanced technologies reveal that dengue virus appears to be associated with platelets and the megakaryocytic lineage. The observation may partially explain the dysfunction of platelets observed in dengue affected patients.

Alternative complement pathway deregulation is correlated with dengue severity

BACKGROUND

The complement system, a key component that links the innate and adaptive immune responses, has three pathways: the classical, lectin, and alternative pathways. In the present study, we have analyzed the levels of various complement components in blood samples from dengue fever (DF) and dengue hemorrhagic fever (DHF) patients and found that the level of complement activation is associated with disease severity.

METHODS AND RESULTS

Patients with DHF had lower levels of complement factor 3 (C3; p = 0.002) and increased levels of C3a, C4a and C5a (p<0.0001) when compared to those with the less severe form, DF. There were no significant differences between DF and DHF patients in the levels of C1q, immunocomplexes (CIC-CIq) and CRP. However, small but statistically significant differences were detected in the levels of MBL. In contrast, the levels of two regulatory proteins of the alternative pathway varied widely between DF and DHF patients: DHF patients had higher levels of factor D (p = 0.01), which cleaves factor B to yield the active (C3bBb) C3 convertase, and lower levels of factor H (p = 0.03), which inactivates the (C3bBb) C3 convertase, than did DF patients. When we considered the levels of factors D and H together as an indicator of (C3bBb) C3 convertase regulation, we found that the plasma levels of these regulatory proteins in DHF patients favored the formation of the (C3bBb) C3 convertase, whereas its formation was inhibited in DF patients (p<0.0001).

CONCLUSION

The data suggest that an imbalance in the levels of regulatory factors D and H is associated with an abnormal regulation of complement activity in DHF patients.

Control of massive bleeding in dengue hemorrhagic fever with severe thrombocytopenia by use of intravenous anti-D globulin

Dengue hemorrhagic fever (DHF) is a potentially lethal complication of mosquito borne viral disease, Dengue Fever. Thrombocytopenia is a constant finding in DHF/Dengue Shock Syndrome (DSS). We report two cases that fulfilled the WHO criteria of DSS: high fever, positive tourniquet test, severe thrombocytopenia (<10,000/mm(3)), hemo-concentration (Hematocrit increase >20%), hypotension and bleeding refractory to routine therapeutic measures, who showed dramatic improvement after receiving Intravenous Anti-D globulin (IV anti-D).

Alternate hypothesis on the pathogenesis of dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS) in dengue virus infection

Dengue fever, caused by infection with dengue virus, is not a new disease, but recently because of its serious emerging health threats, coupled with possible dire consequences including death, it has aroused considerable medical and public health concerns worldwide. Today, dengue is considered one of the most important arthropod-borne viral diseases in humans in terms of morbidity and mortality. Globally, it is estimated that approximate 50 to 100 million new dengue virus infections occur annually. Among these, there are 200,000 to 500,000 cases of potential life-threatening dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS), characterized by thrombocytopenia and increased vascular permeability. The death rate associated with the more severe form DHF/DSS is approximately 5%, predominantly in children under the age of 15. Although intensive efforts have been made to study the early clinical pathophysiology of dengue infection with the objective to identify the potential cause of DHF, results or data that have accumulated from different regions of the world involving studies of different ethnicity groups are inconsistent at present in terms of identifying a unified hypothesis for the pathogenesis of DHF/DSS. Thus, the potential mechanisms involved in the pathogenesis of DHF and DSS remain elusive. The purpose of this review is to identify alternate factors, such as innate immune parameters, hyper-thermal factors, conditioning of neutralizing antibody, concept of vector transmission, and physical status of virus in viremic patients that may play a role in the induction of DHF and DSS, which might have directly or indirectly contributed to the discrepancies that are noted in the literature reported to date. It is the hope that identification of an alternative explanation for the pathogenesis of DHF/DSS will pave the way for the institution of new strategies for the prevention of this complicated disease.

Immunopathogenesis of dengue hemorrhagic fever and shock syndrome: role of TAP and HPA gene polymorphism

Clinical outcomes of dengue infection such as dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS) could be attributed to host genetic factors. The transporters associated with antigen processing (TAP) genes are polymorphic genes located in the human leukocyte antigen (HLA) class II region and are essentially involved in class I antigen presentation. Therefore, these genes might grant susceptibility to severe dengue infection. Hence, the aim of the study was to type the TAP1 gene (using amplification refraction mutation system [ARMS] polymerase chain reaction [PCR]) and HPA1 and HPA2 gene polymorphism (by PCR-sequence specific primers) in different clinical spectrums of dengue infection. The study included 100 controls and 91 DF, 75 DHF, and 32 DSS patients. The results revealed that the frequencies of valine at TAP1 333 and HPA 1b at HPA1 were increased among DHF and DSS, respectively, in comparison to controls (p <0.05). The frequency of genotype TAP1 333 ILE/VAL (61.3%) was significantly higher in DHF compared with control (37%, p = 0.005) or DF (38.9%, p = 0.007) patients. A significantly greater proportion of DHF patients demonstrated HPA1a/1a and HPA 2a/2b genotypes than DF patients. DSS patients were more likely to be heterozygous at HPA1 than DHF (OR = 4.75, p = 0.003). A positive correlation existed between TAP1 333 and HPA1 in DHF (p = 0.017, r = 0.229). This first report on TAP and HPA gene polymorphism in dengue suggested that the heterozygous pattern at the TAP1 333 locus and HPA1a/1a and HPA2a/2b genotypes confer susceptibility to DHF and the HPA1a/1b genotype was determined to be a genetic risk factor for DSS.

Dengue illness: clinical features and pathogenesis

The incidence and geographical distribution of dengue has gradually increased during the past decade. This review is an update on dengue virus infections, based on our clinical and laboratory experiences in the Philippines and on other relevant literature. The differential diagnosis of this disease is discussed, especially for use by clinicians where dengue is not endemic. The complex pathogenesis of thrombocytopenia and increased vascular permeability in dengue illness is also discussed. Our recent data suggest that platelet-associated immunoglobulins involving anti-dengue virus activity play a pivotal role in the development of dengue hemorrhagic fever (DHF), as well as thrombocytopenia in secondary dengue virus infections. Further elucidation is needed on the involvement of platelet-associated immunoglobulins on the molecular mechanisms of thrombocytopenia and the increased vascular permeability.

Association of increased platelet-associated immunoglobulins with thrombocytopenia and the severity of disease in secondary dengue virus infections

Severe thrombocytopenia and increased vascular permeability are two major characteristics of dengue haemorrhagic fever (DHF). To develop a better understanding of the roles of platelet-associated IgG (PAIgG) and IgM (PAIgM) in inducing thrombocytopenia and its severity of disease in patients with secondary dengue virus infection, the relationship between the PAIgG or PAIgM levels and disease severity as well as thrombocytopenia was examined in 78 patients with acute phase secondary infection in a prospective hospital-based study. The decrease in platelet count during the acute phase recovered significantly during the convalescent phase. In contrast, the increased levels of PAIgG or PAIgM that occurred during the acute phase of these patients decreased significantly during the convalescent phase. An inverse correlation between platelet count and PAIgG or PAIgM levels was found in these patients. Anti-dengue virus IgG and IgM activity was found in platelet eluates from 10 patients in an acute phase of secondary infection. Increased levels of PAIgG or PAIgM were significantly higher in DHF than those in dengue fever (DF). An increased level of PAIgM was associated independently with the development of DHF, representing a possible predictor of DHF with a high specificity. Our present data suggest that platelet-associated immunoglobulins involving antidengue virus activity play a pivotal role in the induction of thrombocytopenia and the severity of the disease in secondary dengue virus infections.

Manipulation of cell surface macromolecules by flaviviruses

Cell surface macromolecules play a crucial role in the biology and pathobiology of flaviviruses, both as receptors for virus entry and as signaling molecules for cell–cell interactions in the processes of vascular permeability and inflammation. This review examines the cell tropism and pathogenesis of flaviviruses from the standpoint of cell surface molecules, which have been implicated as receptors in both virus–cell as well as cell–cell interactions. The emerging picture is one that encompasses extensive regulation and interplay among the invading virus, viral immune complexes, Fc receptors, major histocompatibility complex antigens, and adhesion molecules.

Correlation between increased platelet-associated IgG and thrombocytopenia in secondary dengue virus infections

Although the public health impact of dengue is increasing rapidly, the mechanism of thrombocytopenia in this disease remains unknown. To elucidate this mechanism, the relationship between platelet-associated IgG (PAIgG) and platelet count in 53 patients in the acute phase of secondary dengue virus infection was investigated in a prospective-hospital-based study. A significant inverse correlation between the two parameters was found in these patients, while no correlation was observed in healthy volunteers. The low baseline platelet counts during the acute phase in 12 patients with secondary dengue virus infection significantly increased during the convalescent phase, while the increased PAIgG levels during the acute phase in these patients significantly decreased during the convalescent phase. Anti-platelet IgG autoantibody was detected rarely in the plasma of 53 patients with secondary dengue infection. The involvement of anti-dengue virus IgG was also shown in platelets from all of 8 patients in the acute phase of secondary dengue virus infection. These findings suggest that PAIgG formation involving anti-dengue virus IgG plays a pivotal role in the induction of transient thrombocytopenia during the acute phase of secondary dengue virus infection.

Coagulation abnormalities in dengue hemorrhagic Fever: serial investigations in 167 Vietnamese children with Dengue shock syndrome

The pathophysiological basis of hemorrhage in dengue infections remains poorly understood, despite the increasing global importance of these infections. A large prospective study of 167 Vietnamese children with dengue shock syndrome documented only minor prolongations of prothrombin and partial thromboplastin times but moderate to severe depression of plasma fibrinogen concentrations. A detailed study of 48 children revealed low plasma concentrations of the anticoagulant proteins C, S, and antithrombin III, which decreased with increasing severity of shock, probably because of capillary leakage. Concurrent increases in the levels of thrombomodulin, tissue factor, and plasminogen activator inhibitor type 1 (PAI-1) indicated increased production of these proteins. Thrombomodulin levels suggestive of endothelial activation correlated with increasing shock severity, whereas PAI-1 levels correlated with bleeding severity. Dengue virus can directly activate plasminogen in vitro. Rather than causing true disseminated intravascular coagulation, dengue infection may activate fibrinolysis primarily, degrading fibrinogen directly and prompting secondary activation of procoagulant homeostatic mechanisms.

Hemorrhagic fever virus-induced changes in hemostasis and vascular biology

Viral hemorrhagic fever (VHF) denotes a virus-induced acute febrile, hemorrhagic disease reported from wide areas of the world. Hemorrhagic fever (HF) viruses are encapsulated, single-stranded RNA viruses that are associated with insect or rodent vectors whose interaction with humans defines the mode of disease transmission. There are 14 HF viruses, which belong to four viral families: Arenaviridae, Bunyaviridae, Filoviridae and Flaviviridae. This review presents, in order, the following aspects of VHF: (1) epidemiology, (2) anomalies of platelets and coagulation factors, (3) vasculopathy, (4) animal models of VHFs, (5) pathogenic mechanisms, and (6) treatment and future studies. HF viruses produce the manifestations of VHFs either by direct effects on cellular functions or by activation of immune and inflammatory pathways. In Lassa fever, Rift Valley fever and Crimean-Congo HF, the main feature of fatal illness appears to be impaired/delayed cellular immunity, which leads to unchecked viremia. However, in HF with renal syndrome and dengue HF, the immune response plays an active role in disease pathogenesis. The interplay of hemostasis, immune response, and inflammation is very complex. Molecular biologic techniques and the use of animal models have helped to unravel some of these interactions.

Haematology in dengue and dengue haemorrhagic fever

Dengue fever (DF) and dengue haemorrhagic fever (DHF) are caused by the dengue virus. The major pathophysiological hallmark that distinguishes DHF from DF is plasma leakage as a result of increased vascular permeability. Following this leakage, hypovolaemic shock occurs as a consequence of a critical plasma volume loss. Constant haematological abnormalities occurring in DHF and frequently include bone marrow suppression, leucopenia and thrombocytopenia. An enhanced immune response of the host to a secondary DV infection is a feature of DHF and leads to many consequences. These are immune complex formation, complement activation, increased histamine release and a massive release of many cytokines into the circulation, leading to shock, vasculopathy, thrombopathy and disseminated intravascular coagulation (DIC). The mechanisms underlying the bleeding in DHF are multiple. These are vasculopathy, thrombopathy and DIC. Thrombopathy consists of thrombocytopenia and platelet dysfunction. DIC is prominent in patients with shock. The most severe DIC and massive bleeding are the result of prolonged shock and cause a fatal outcome. The mechanisms of thrombopathy and DIC and the proper management of DHF are reviewed and discussed.

Subcellular changes in platelets in acute and subacute African swine fever

The morphological changes in platelets in acute and subacute African swine fever (ASF) and their relationship to pathogenesis were studied. Eight pigs were inoculated with a highly virulent strain of African swine fever (Malawi '83) and 14 with a moderately virulent strain (Dominican Republic '78) for ultrastructural study of platelets, monocyte/macrophages and vascular structures in the liver, spleen, lymph node, bone marrow, lung and kidney. Both viruses produced activation and degranulation of platelets from day 3 after inoculation onwards, coinciding with activation of the mononuclear phagocyte system and virus replication in monocyte/macrophages. Platelet aggregation and viscous metamorphosis of platelets were observed at 5 and 7 days after inoculation with the highly virulent strain, coinciding with endothelial alterations, but platelet aggregation was less prevalent and there was no sign of viscous metamorphosis in animals inoculated with the moderately virulent strain. Virions within platelets were observed at the final stage of acute ASF and at 5-7 days after inoculation in subacute ASF. This suggests that platelets assist in disseminating ASF virus within the body, especially in subacute infections.

Diagnosing dengue virus infection in archived autopsy tissues by means of the in situ PCR method: a case report

BACKGROUND

The pathogenesis of the severe form of dengue virus infection, dengue hemorrhagic fever, is still obscure. A major research objective has been to determine which body organs are being damaged by dengue virus in this form of dengue. Research has been difficult because dengue hemorrhagic fever is sporadic and tends to occur in parts of the world where modern facilities are scarce and fresh or frozen patient materials are not available. However, major hospitals in these areas have accumulated libraries of paraffin-embedded surgical and autopsy tissues over the years. These tissues may have been subjected to less than optimal fixation and storage. Attempts to localize dengue virus using antigen detection in the stored tissue have encountered many difficulties.

OBJECTIVE

Since viral nucleic acid may be preserved under circumstances which destroy protein antigens, our objective was to detect dengue viral RNA in situ in histologic sections of tissues from patients dying of dengue hemorrhagic fever in Thailand.

STUDY DESIGN

Tissues from an 11-year-old boy who died at Ramathibodi Hospital, Bangkok, Thailand in November, 1987 with the clinical diagnosis of dengue hemorrhagic fever were treated by transcribing the dengue viral RNA to DNA followed by amplification using the polymerase chain reaction with subsequent in situ hybridization in order to visualize the cells infected with dengue virus.

RESULTS

Viral RNA was detected in hepatocytes in the mid-zonal region of the liver, as well as scattered macrophages in skin and lymph nodes.

CONCLUSION

Dengue virus infection can be detected in paraffin-embedded autopsy tissues which have been stored for five years. The same procedure can be used for diagnosing dengue viral infection and for studying the pathogenesis of dengue hemorrhagic fever.

Pathogenesis of dengue: challenges to molecular biology

Dengue viruses occur as four antigenically related but distinct serotypes transmitted to humans by Aedes aegypti mosquitoes. These viruses generally cause a benign syndrome, dengue fever, in the American and African tropics, and a severe syndrome, dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), in Southeast Asian children. This severe syndrome, which recently has also been identified in children infected with the virus in Puerto Rico, is characterized by increased vascular permeability and abnormal hemostasis. It occurs in infants less than 1 year of age born to dengue-immune mothers and in children 1 year and older who are immune to one serotype of dengue virus and are experiencing infection with a second serotype. Dengue viruses replicate in cells of mononuclear phagocyte lineage, and subneutralizing concentrations of dengue antibody enhance dengue virus infection in these cells. This antibody-dependent enhancement of infection regulates dengue disease in human beings, although disease severity may also be controlled genetically, possibly by permitting and restricting the growth of virus in monocytes. Monoclonal antibodies show heterogeneous distribution of antigenic epitopes on dengue viruses. These epitopes serve to regulate disease: when antibodies to shared antigens partially neutralize heterotypic virus, infection and disease are dampened; enhancing antibodies alone result in heightened disease response. Further knowledge of the structure of dengue genomes should permit rapid advances in understanding the pathogenetic mechanisms of dengue.

Platelet-associated IgG in hepatitis and cirrhosis

Increasing evidence is accumulating which indicates that immunological abnormalities contribute to the development of liver disease and its signs and symptoms. Platelet-associated IgG (PAIgG) levels were quantified in 42 patients with biopsy-proven liver disease of various etiologies to determine the relationship of thrombocytopenia to immunologic abnormalities in these disorders. Five of six nonthrombocytopenic patients with acute viral hepatitis B had elevated PAIgG. Six of ten patients with chronic active hepatitis had elevated PAIgG and thrombocytopenia. In contrast, only one of six patients with chronic persistent hepatitis had elevated PAIgG. Nine of ten patients with alcoholic hepatitis had elevated PAIgG; seven of the nine were thrombocytopenic. Seven of ten alcoholic patients with cirrhosis had elevated PAIgG; six of seven were thrombocytopenic. Thus the increase in PAIgG may be present without thrombocytopenia in acute liver injury, while patients with chronic persistent hepatitis do not usually exhibit this abnormality. Severe chronic active liver disease is accompanied by thrombocytopenia and an increase in PAIgG levels.