T Cell Immunopathogenesis of Dengue Virus Infection

T Cell Immunopathogenesis of Dengue Virus Infection

Lokesh Guglani and S.K. Kabra!

Department of Paediatrics, All India Institute of Medical Sciences, New Delhi - 110 029, India

Abstract

Dengue virus infections cause significant morbidity and mortality worldwide. Although initially believed to be an infection afflicting mainly the paediatric age group, this infection has been rapidly spreading across all age groups, with the first reports of the pandemic from South-East Asia dating back to the 1950s. Dengue virus belongs to the genus Flavivirus and has four serotypes, each of which may cause a spectrum of illness ranging from asymptomatic to mild febrile illness to severe and often fatal haemorrhagic disease. Despite our growing understanding of various facets of the infection, its pathogenesis still remains unclear, with the possibility of several mechanisms being involved simultaneously. The virus is taken up by dendritic cells, which, after antigen processing, presents it to T cells, leading to immune activation and release of a cascade of cytokines that are believed to mediate the systemic effects of plasma leakage and circulatory insufficiency. Thrombocytopenia develops due to the presence of cross-reacting antibodies to platelets and is responsible for the bleeding diathesis. The phenomenon of ‘original antigenic sin’ may explain the increased severity of illness during secondary infections, due to the presence of antibody to the previously infecting serotype. This leads to immune enhancement leading to the development of dengue shock syndrome (DSS). In addition, there is evidence for increased apoptosis and endothelial cell dysfunction, which may also contribute to its pathogenesis. Dengue virus infection in infants may cause increased morbidity due to the presence of pre-existing maternal antibodies in endemic areas. Several advances have been made in the treatment of acute infections, and recent preventive efforts have been directed towards the development of safe and effective vaccines against all the four serotypes in order to provide lasting protection from this dreaded infection, which still causes high morbidity and mortality in most developing countries.

Keywords: Dengue, dengue haemorrhagic fever, dengue shock syndrome, immunopathogenesis, dengue vaccines.

Introduction DENV-1, DENV-2, DENV-3 and DENV-4. It causes a spectrum of infection ranging from The dengue virus infection is prevalent across mild febrile illness to severe and often fatal the tropical belt in over 100 countries, with haemorrhagic disease. 2.5 billion people at risk of acquiring the infection and an estimated 50 million infections Despite our growing understanding of the and 500 000 dengue haemorrhagic fever (DHF) various facets of dengue virus infection, the cases occurring annually[1,2]. Dengue virus pathogenesis of dengue still remains unclear. belongs to the genus Flavivirus, family Although several mechanisms may be involved Flaviviridae and has four serotypes, called simultaneously, their relative importance

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58 Dengue Bulletin – Vol 29, 2005 T Cell Immunopathogenesis of Dengue Virus Infection remains undefined. This article reviews our and thrombocytopenia. Liver enzyme levels current knowledge of the pathogenesis of may be mildly elevated. dengue virus infection and the implications of ongoing research in improving our Dengue haemorrhagic fever (DHF) is a understanding of this dreaded infection. severe manifestation of dengue fever and generally affects children less than 15 years of The publications reviewed for this article age. It is characterized by a similar initial course were obtained using the Medline search with but there is onset of haemorrhagic manifestations terms “dengue and immunopathogenesis” and and circulatory insufficiency within or just 24 “dengue and pathogenesis”. The search was hours before remission of fever. The severity is further refined by adding “children” to the graded by the World Health Organisation above terms to specifically look for dengue (WHO) grading and grade III and IV represent infection in children <15 years of age. dengue shock syndrome (DSS), with circulatory insufficiency in addition to bleeding Dengue fever (DF) is caused by ingestion manifestations. Laboratory abnormalities include of viraemic blood containing dengue virus by leukopenia, thrombocytopenia and mosquitoes of Aedes spp. followed by passage haemoconcentration with primary patho- to a second human host. An extrinsic physiological abnormality being an acute increase incubation period of 8–10 days is required in vascular permeability leading to extravasation before the virus appears in the saliva of the of fluid, haemoconcentration and hypotension. transmitting female Aedes mosquito. After the There is plasma leakage into the serous cavities bite, there is an incubation period of 3 to 14 also and hepatomegaly with raised liver enzymes days (average 4 to 7 days) followed by the onset is not uncommon. DHF and DSS require of fever and non-specific signs and symptoms aggressive fluid therapy and supportive (frontal headache, retro-orbital pain, body management for haemorrhagic manifestations aches, nausea and vomiting, joint pains, but have a high mortality rate if not addressed weakness and rash). This febrile phase is self- early in their course. There are no apparent limiting and may last for 2 to 10 days followed destructive vascular lesions, suggesting that a by remission of fever in most cases. Laboratory short-acting mediator may be causing transient [3] abnormalities include neutropenia followed by functional vascular changes . Several risk factors a lymphocytosis (usually atypical lymphocytes) for the occurrence of DHF/DSS have been identified (Table).

Table. Risk factors for DHF/DSS

• Virus strain: epidemic potential, risk of DHF is greatest for DENV-2 followed by DENV-3, DENV-4 and DENV-1 • Pre-existing anti-dengue antibody • Age of host • Genetics • Secondary infection • Hyperendemicity – two or more virus serotypes may be circulating simultaneously at high level.

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Immunopathogenesis low-level release of IL-12p70, a key cytokine in the development of cell mediated immunity The first contact of the dengue virus with the (CMI). immune system is when it encounters dendritic γ cells (DCs) in the tissues (Figure). These Addition of IFN- at this stage (in vitro) resulted in the enhancement of IL-12p70 dedicated antigen-presenting cells (APCs) γ internalize the virus where it resides in cystic synthesis, suggesting that IFN- is an important vacuoles, vesicles and endoplasmic reticulum. second signal for secretion of bioactive IL-12 There are then two stages in DC development from DCs in addition to its effect on expression of molecules involved in stimulating antigen- – the first one being immature stage, where [5] the DCs primarily phagocytose and process the specific T cell response . This may be a antigen. The mature stage is characterized by regulatory mechanism for preventing potentially up-regulation of expression of CD83, other co- harmful Th1 type immune response early in stimulatory and HLA DR molecules for the pathogenesis of acute dengue virus effective antigen presentation to T cells. Once infection without the associated anamnestic these cells undergo maturation, they release a burst of cytokines. During a secondary dengue α infection, memory T cells would produce early number of cytokines, including TNF- and IFN- γ α that have specific roles in pathogenesis. TNF- IFN- and CD40L in the DC micro- α and IFN-α also lead to activation of other environment leading to greater DC activation virus infected and non-infected DCs in a and subsequent T cell stimulation and cytokine paracrine manner[4]. Simultaneously, there is release, especially IL-12p70. The viraemia may

Figure. Possible immunopathogenetic mechanisms of dengue virus infection

60 Dengue Bulletin – Vol 29, 2005 T Cell Immunopathogenesis of Dengue Virus Infection be cleared but the cascade of events initiated a study of T cell function, subjects were Thai by the early, poorly controlled type 1 cytokine schoolchildren who were enrolled prospectively response contributes to the pathogenesis of and their pre-illness blood samples were taken DHF/DSS. Various studies have shown higher and preserved[7]. They were then followed up levels of TNF-α, soluble TNF-α receptor and for development of any episode of fever (based IFN-γ levels in patients with DHF/DSS as on their school absence) and were then compared to those with dengue fever. evaluated and blood samples (acute and convalescent) were taken during active dengue The dendritic cells also phagocytose other infection (which was confirmed by virus virus-infected cells undergoing apoptosis. The isolation and/or RT PCR). This gave the DC maturation process can be regulated by a researchers the opportunity to study the various variety of stimuli such as cytokines, viral products cellular and humoral immune parameters and and CD40 ligand. A number of organisms like compare them with pre-illness sample of the measles virus, influenza virus, P. falciparum, T. same subject. If the subject’s pre-illness sample cruzi etc. also modulate the DC maturation had antibodies to dengue virus, then the process as part of their pathogenesis to influence present acute episode obviously represented the immune response. These infected cells then secondary infection. migrate from peripheral tissues to lymph nodes and activate CD4+ and CD8+ T lymphocytes It also showed that a subset of patients for the generation of adaptive immune response. might not develop DHF/DSS on secondary However, most of the studies using dengue infection with dengue virus. These patients virus have used peripheral blood myeloid DCs were shown to have no proliferation or cytokine to characterize these interactions, assuming response to any of the dengue antigens but that they are equivalent to the interstitial DCs had definite evidence of prior dengue virus that actually encounter the virus after the initial infection in the form of detectable pre-infection mosquito bite[6]. There is some evidence of neutralizing anti-dengue virus antibody titres. direct infection of B cells also with the virus, This was thought to be due to very low CD4 T leading to similar pathogenetic mechanisms as cell response during the initial primary infection in DCs, such as the synthesis of cytokines (IL- and/or T cell response having waned over time. 6, TNF-α) and that of cross-reacting auto antibodies against platelets and endothelial The serotype-specific T cells generated cells. after primary infection recognize the more highly conserved non-structural proteins of dengue virus (especially NS3 protein). They are Role of T Cells both of CD4 and CD8 type, with pattern and magnitude of cross-reactive response to the T lymphocytes have a central role in the other serotypes being highly variable among immune response to dengue virus infection. T the same subjects, even among those infected cell function in primary infection stage show with the same virus[8]. In addition to synthesis varied patterns of T cell responses, which of cytokines to mediate their effects (discussed indicate that host response is complex and below), the dengue virus-specific T cells lyse different patterns of proliferation and cytokine other virus-infected cells by perforin-dependent formation may bring about varied outcomes. mechanisms and also cause Bystander Cell Lysis Interactions between pre-existing T cell of the uninfected cells. The latter effect is responses and other host and viral factors may mediated via Fas Ligand (FasL) expressed on also be important in determining outcome. In the surface of activated T cells that binds to

Dengue Bulletin – Vol 29, 2005 61 T Cell Immunopathogenesis of Dengue Virus Infection the Fas molecules on the ‘innocent’ bystander Serotype cross-reactive antibodies cells. This effect has been demonstrated in vitro generated from previous primary infection with in uninfected HepG2 cell line cultured with a particular dengue viral serotype are not highly dengue virus-specific CD4 T cell clones. specific for the other serotypes involved in secondary infections. Hence they bind to the Reversal of CD4 and CD8 ratio has been virions but do not neutralize them, and instead reported in a proportion of cases and their increase their uptake by cells which express numbers are significantly higher among those Fcγ receptors on their surfaces - like tissue with DHF/DSS. It reverts back to normal by the dendritic cells, monocytes and macrophages. 15th day of illness and represents aberrant Such antibody-coated virions are taken up more immune activation and ongoing apoptosis rapidly than uncoated virus particles and this (discussed below). Markers of T cell activation leads to enhanced antigen presentation by the (soluble IL-2 receptor, soluble CD4, CD8 and infected dendritic cells to the T cells, leading monokines) are found at higher levels in patients to the more rapid activation and proliferation with DHF/DSS as compared to those with DF, of memory T cells. The cytokines produced by suggesting greater T cell activation in the the activated T cells have several important former[9]. The expansion of T cell receptors using effects that lead to the pathogenesis of DHF/ Vβ genes is also associated with increased DSS. severity in several diseases. In an attempt to study the biological basis of T cell activation in However, the evidence for the occurrence dengue infection, T cell Vβ gene usage studies of antibody-dependent enhancement in vivo were done in Thai children. It showed no is circumstantial, as it has only been difference in its expression in those with dengue demonstrated in vitro in sera from infected fever when compared to those with DHF[10]. children[12]. Furthermore, there is no evidence from clinical studies to show that secondary infections are associated with higher titres of Secondary Infection or viremia as compared to primary infection[13]. Immune Enhancement Hypothesis Role of Cytokines

This is an essential component of the Cytokines are implicated in the pathogenesis pathogenesis of DHF, which explains why some of vascular compromise and haemorrhage in individuals with acute dengue viral infection dengue virus infection. The evidence for their present as dengue fever while others go on to involvement came from the observations of develop DHF and/or DSS. Halstead proposed Innes, who suggested that the lack of structural the mechanism of antibody-dependent damage, short-lived nature of the plasma enhancement whereby pre-existing non- leakage and remarkably rapid recovery suggest neutralizing antibodies opsonize the virus and that altered permeability may be due to a enhance its uptake and replication in soluble mediator[14]. macrophages. This leads to a higher viral load and enhanced antigen presentation resulting The release of cytokines in response to in extensive T cell activation. This extensive dengue viral infection includes both activation supposedly causes the T cells to inflammatory as well as inhibitory cytokines and become “stunned”, whereby their IFN-γ the net outcome will depend on the balance expression remains low[11]. between various cytokine actions. There is an

62 Dengue Bulletin – Vol 29, 2005 T Cell Immunopathogenesis of Dengue Virus Infection overall increase in the levels of T cell activation proliferating in response to the currently markers such as soluble IL-2 receptor, soluble infecting virus and that it could induce the CD4 and CD8, IL-2 and IFN-γ as well as that proliferation of a spectrum of clones with of monokines like TNFα, IFN-β and GM-CSF, differing affinities and cross-reactivities. and these levels were consistently higher in Therefore, secondary infection with a virus those with DHF/DSS as against those with carrying a similar but distinct epitope stimulates DF[15]. IL-6 has dual role of being pro- and anti- the proliferation of cross-reacting, low-affinity inflammatory and it shows transient high clones and this characterizes the phenomenon elevation on day 7 or day 9–11 after onset of of original antigenic sin. fever[16]. Dengue patients with shock have significantly higher levels of IL-6 at admission Further insights were provided into this as compared to normotensive patients and it mechanism by the work of Screaton et al.[19] is also associated with higher incidence of who studied the virus-specific T cell responses ascites. Similarly, high levels of IL-8 were in acutely infected Thai children. It was found recovered from the serum and pleural fluid of that few dengue-responsive CD8+ T cells were patients with DSS[17]. Chaturvedi et al. have found during acute infection and most of these also postulated the presence of a unique had a low affinity for the infecting virus cytokine called human cytotoxic factor (HCF), serotype. That is, the original exposure to the which is believed to initiate a series of events dengue virus of a different serotype caused leading to a shift from Th1-type response in the T cell responses to become suppressed, mild illness to Th2-type response that leads to thus delaying viral elimination and leading to DHF[18]. higher viral loads, with possible increased immunopathology. The authors proposed that profound T cell activation and death may Original Antigenic Sin contribute to systemic disturbances leading to DHF. This phenomenon is applicable to secondary challenge by a pathogen where the response is dominated by the proliferation of cross- Apoptosis reacting memory cells which were initially induced by the primary infection, but they may The dengue virus infects the monocyte/ be of lower affinity to the secondarily macropahge cell lineage and the ability of challenging pathogen. The T cell responses for dendritic cells (DCs) to shape the adaptive secondary dengue viral infections also immune response to viral infection is mediated demonstrate this phenomenon, which may largely by their maturation and activation state, eventually delay or suppress viral elimination, as determined by the surface expression of HLA leading to higher viral loads and thus increased molecules, costimulatory molecules and immunopathology[19]. The initial evidence for cytokine production[20]. this phenomenon came from the observations that in secondary infections with DENV-1, many After entrance, dengue virions can be T cells showed a preference for DENV-3 visualized in cystic vesicles, vacuoles and the tetramers and in DENV-2 infections there was endoplasmic reticulum. The dengue virus- better reaction with DENV-1 and DENV-3 infected DC also shows proliferation and tetramers initially. The response increased in hypertrophy of the endoplasmic reticulum as later samples suggesting that these cells were well as swollen mitochondria[21].

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Viral replication occurs within these cells is generation of antibodies against dengue virus and also leads to further dissemination of the proteins (especially NS1), which cross-react virus. Once the cell is activated, it releases a with platelet surface proteins and thus cause number of soluble mediators including TNF-α, thrombocytopenia[24]. These antibodies, which alter the biological properties of besides causing platelet lysis via complement endothelial cells. More specifically, it is also activation, also inhibit ADP-induced platelet believed to induce apoptosis among these cells aggregation[25]. The titre of these IgM antibodies as an indirect attempt to limit viral replication. has been found to be much higher in patients The study of human monocyte cultures with DHF/DSS than in those with dengue fever. infected with DENV-2 viruses showed increased production of TNF-α and increased apoptosis, but the production of nitric oxide was not Endothelial Dysfunction in increased[22]. Dengue Fever In addition, there is evidence to show that endothelial cells also undergo apoptosis, which Endothelial cell dysfunction in dengue virus causes disruption of endothelial cell barrier, infection manifests as diffuse increase in leading to the syndrome of generalized vascular capillary permeability, which is responsible for leakage[23]. Antibodies against viral protein NS1 the microvascular leakage, haemoconcentration (non-structural protein) generated in mouse and circulatory insufficiency. The transient animal model cross-react with mouse as well nature of plasma leakage suggests that it’s as human endothelial cells. The binding of probably mediated by a soluble mediator. these antibodies to endothelial cells led to an Studies have shown that infection of endothelial increased expression of inducible NO synthase cells with dengue virus induces transcriptional (iNOS) and subsequently increased production up-regulation and secretion of RANTES and IL- of nitric oxide (NO). Further evaluation of the 8 and extremely high levels of IL-8 have also been detected in plasma and pleural fluid signaling pathways showed the involvement of [17] caspase-dependent mechanism, which samples from patients with DSS . involved up-regulation of pro-apoptotic factors Assessment of microvascular leakage using (p53 and Bax) and down regulation of anti- strain gauge plethysmography in children with apoptotic factors (bcl-2 and bcl-xl) in the DHF and DSS found that although the endothelial cells. These changes were not coefficient of microvascular permeability (K ) observed when inhibitor of iNO (L-NAME) was f was higher in children with either DHF or DSS added to the cells, suggesting the role of NO as against healthy controls, there was no in inducing endothelial cell dysfunction and significant difference in the two groups as well, plasma leakage. suggesting similar pathogenetic mechanism. Since each recording takes 45 minutes, the measurements in children with DSS were made Thrombocytopenia in after the initial fluid resuscitation. However,

Dengue Fever the fluctuations in Kf were larger in children with DSS as against those with DHF, leading to Dengue viral infection is commonly associated short-lived peaks of markedly increased with thrombocytopenia, the cause of which is microvascular permeability and consequent molecular mimicry between dengue virus circulatory insufficiency. Irrespective of the proteins and endogenous self-proteins. There presence of shock, all patients with dengue

64 Dengue Bulletin – Vol 29, 2005 T Cell Immunopathogenesis of Dengue Virus Infection virus infection demonstrate volumotion, which be truly determined but a higher incidence of implies slow-wave cyclical changes in limb convulsions in infants with dengue has been circumference probably due to underlying reported by others. The infants were also found vasomotion – i.e. periodic change in arteriolar to have more pronounced thrombocytopenia diameter. The latter could be a compensatory but the complications due to bleeding were mechanism to improve tissue oxygenation and less pronounced than in older children[30]. blood flow to prevent hypoxic damage in the face of circulatory insufficiency. The authors postulated the presence of a probable Recent Advances in Therapy hypothetical threshold for shock, beyond which increases in microvascular permeability result As our understanding about the pathogenesis in DSS[26]. of dengue virus infection improves, new interventions might help improve the outcome of this oft-fatal infection. The recent use of Effect of Maternal Antibodies anti-TNF-α serum in the mouse model of DENV- 2 infection reduced the mortality rate Infants less than one year of age who acquire significantly (from 100% in untreated to 40% maternal anti-dengue IgG antibody may be at in treated animals, P<0.05)[31]. This risk of DHF/DSS even during primary intervention was based on the fact that TNF-α infection[27]. At the same time, the occurrence was significantly raised in patients with DHF/ of sequential primary infection with different DSS as against those with dengue fever. virus serotypes in these infants cannot be ruled However, it may take a while before this out. Hence, in the presence of pre-existing promising approach could be applied in humans maternal antibodies against dengue virus in as well. Other drugs that have been tried these infants, the occurrence of even primary include ribavirin, a guanosine analogue for RNA infection in this age group can lead to severe viruses, which has been shown to inhibit manifestations due to the phenomenon of dengue virus replication and IL-6 and IL-8 immune enhancement. production in endothelial cells. Amantadine has also been tried and carboxyfullerene, a novel The data from recent epidemics from India compound with anti-oxidant properties, has the show variable rates of occurrence of DHF/DSS ability to inactivate the dengue virus in a light- versus dengue fever in the age group of <1 dependent manner. year. In the Delhi epidemic of 1996, 9% of infants presented with signs of DHF, the There has been an attempt to reduce the youngest one being 3 months of age[28], while mortality associated with DSS by using more data from the recent Chennai epidemic aggressive fluid therapy than that suggested by (September 2001–January 2002)[29] showed WHO. Although no significant differences were higher proportion of DSS in infants as compared demonstrated among the various fluid types to that in older children (overall 20% of cases used for the initial resuscitation, but colloids’ being infants). The Chennai study also showed use may be associated with most rapid a higher incidence of convulsions, drowsiness, normalization of haematocrit and restoration orbital puffiness and rash in infants; while of cardiac index[32]. vomiting, restlessness and abdominal pain were predominant in older children. Whether An alternative protocol suggests the use the occurrence of convulsions in infants was of greater amounts of fluids, and, there has due to fever or dengue infection per se cannot been interest in the use of aggressive fluid

Dengue Bulletin – Vol 29, 2005 65 T Cell Immunopathogenesis of Dengue Virus Infection removal strategies of the excess fluid to vaccines and the other two have been made decrease the overall morbidity and mortality by passaging dengue viruses in non-human in children with DHF[33]. tissue cultures.

In addition, there has been ongoing The first vaccine was developed at Mahidol development of peptide inhibitors of dengue University in Bangkok, Thailand, and licensed virus infectivity which hold promise for by Aventis Pasteur. It produces 80–90% development as antiviral peptide drugs for seroconversion rates to all four serotypes after these infections[34]. These peptides mimic the the administration of two doses in young alpha portion of the viral fusion proteins, which children[39]. The second vaccine, produced by help to mediate cell entry of the virus and thus the Walter Reed Army Institute of Research, check the entry of the virions into cells. Another USA, and licensed by GlaxoSmithKline, exciting group of compounds, the alpha- produced similar seroconversion rates in adult glucosidase inhibitors, comprising of volunteers. But the molecular basis of castanospermine and deoxynojirimycin, inhibit attenuation by these vaccines is not understood type virus infection both in vitro and in vivo, and it is believed that interference in replication possibly by disrupting the folding of structural between the serotypes and/or interference in proteins prM and E, a step which is crucial for immune stimulation may lead to imbalanced viral secretion[35]. Two sulfated polysaccharides immune responses resulting in incomplete obtained from the red seaweeds, protection and enhanced disease severity. In Gymnogongrus griffithsiae and Cryptonemia addition, reversion to virulence through crenulata, have also shown activity against mutation or recombination between the dengue virus serotype 2 and the initial vaccine components or with wild virus, are processes of virus adsorption and internalization causes for concern. are the main targets of these compounds[36]. The most recent evaluation of DENV-2 inactivated, recombinant subunit and live- Vaccines attenuated vaccine candidates in the rhesus macaque model[40] has shown encouraging Dengue viruses are small, single-strand, results. While this data is from animal studies positive-sense RNA Flaviviruses with similar only, it represents an important step towards genetic organization and replication strategies demonstrating the safety, efficacy and as those of yellow fever and Japanese immunogenicity of these potential vaccine encephalitis viruses[37]. By replacing the pre- candidates. membrane and envelope genes of yellow fever 17D vaccine with those of Japanese Considering the disease burden and encephalitis (JE) virus, unique live-attenuated significant dengue-associated morbidity and chimeric vaccines have been generated for JE mortality, a review of the cost-effectiveness of by Thomas Monath and colleagues[38]. This dengue vaccines found their implementation vaccine had no unusual side effects and to be cost-effective. A meeting of the [41] generated high titres of neutralizing antibodies Pharmaco-economic Working Group to JE virus. A similar approach has also been concluded that it would cost $0.50 per dose tried for dengue by making chimera vaccines in the public sector and $10 per dose in the with all four dengue virus strains. At present, private sector, the overall average cost for there are six vaccines in late stages of vaccinating one child being $7.58. The gross development – four of them being chimera cost of the vaccination programme per 1000

66 Dengue Bulletin – Vol 29, 2005 T Cell Immunopathogenesis of Dengue Virus Infection population in South-East Asia would be $154 decisions in affected countries of South-East and the overall cost per disability-adjusted-life- Asia[42]. year (DALY) saved would be $50. In view of the overall savings in health care costs due to reduction in cases of DHF, the net cost per Conclusion capita would be $17. This data is from 10 South- East Asian countries (Brunei, Cambodia, The dengue pandemic started some time Indonesia, Laos, Malaysia, Myanmar, during World War II and has spread Philippines, Singapore, Thailand and Viet Nam) progressively to involve almost all tropical and does not include India, so there is a need countries. It has caused about 5 million to evaluate the disease profile in our country hospitalizations in children and about 70 000 and formulate similar cost-effective measures deaths from DHF/DSS. Widespread failure of to assess the feasibility of vaccine mosquito control programmes has led to implementation. expanded efforts in the development of the tetravalent dengue vaccine. It is hoped that in Paediatric Dengue Vaccine Initiative (PDVI) the coming 10 years this public health menace is a forum for coordination of global efforts in could be checked by the use of safe and dengue vaccine development under the aegis effective vaccines. As we gain more insight into of International Vaccine Institute, Seoul. It was the pathogenetic mechanisms of dengue virus launched in February 2002 and has been active infections, we can hope to improve our efforts in collecting information on the disease burden, towards providing better case management to drafting vaccine research and development reduce its overall morbidity and mortality and proposals and influencing policy-makers’ assist in the development of safe and effective vaccines against this dreaded disease.

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