|A TEM micrograph showing dengue virus virions (the cluster of dark dots near the center).|
|Group:||Group IV ((+)ssRNA)|
The dengue virus (DENV) in one of five serotypes is the cause of dengue fever. It is a mosquito-borne single positive-stranded RNA virus of the family Flaviviridae; genus Flavivirus. All five serotypes can cause the full spectrum of disease.
Its genome is about 11000 bases that codes for three structural proteins, capsid protein C, membrane protein M, envelope protein E; seven nonstructural proteins, NS1, NS2a, NS2b, NS3, NS4a, NS4b, NS5; and short non-coding regions on both the 5' and 3' ends. Further classification of each serotype into genotypes often relates to the region where particular strains are commonly found or were first found.
- 1 Evolution
- 2 Life cycle
- 3 Structure
- 4 Immune system interaction
- 5 References
- 6 External links
The dengue type 1 virus appears to have evolved in the early 19th century. Based on the analysis of the envelope protein there are at least four genotypes (1 to 4). The rate of nucleotide substitution for this virus has been estimated to be 6.5×10−4 per nucleotide per year, a rate similar to other RNA viruses. The American African genotype has been estimated to have evolved between 1907 to 1949. This period includes World War I and II which were associated with considerable movement of populations and environmental disturbance, factors known to promote the evolution of new vector borne viral species.
Until a few hundred years ago dengue virus was transmitted in sylvatic cycles in Africa and Asia between mosquitoes of the genus Aedes and non-human primates with rare emergences into human populations. The global spread of dengue virus, however, has followed its emergence from sylvatic cycles and the primary life cycle now exclusively involves transmission between humans and Aedes mosquitoes. Vertical transmission from mosquito to mosquito has also been observed in some vector species.
The DENV E (envelope) protein, found on the viral surface, is important in the initial attachment of the viral particle to the host cell. Dengue virus is transmitted by a mosquito known as Aedes. Several molecules which interact with the viral E protein (ICAM3-grabbing non-integrin, CD209, Rab 5, GRP 78, and the mannose receptor ) have been shown to be important factors mediating attachment and viral entry.
The DENV prM (membrane) protein, which is important in the formation and maturation of the viral particle, consists of seven antiparallel β-strands stabilized by three disulfide bonds.
The glycoprotein shell of the mature DENV virion consists of 180 copies each of the E protein and M protein. The immature virion starts out with the E and prM proteins forming 90 heterodimers that give a spiky exterior to the viral particle. This immature viral particle buds into the endoplasmic reticulum and eventually travels via the secretory pathway to the Golgi apparatus. As the virion passes through the trans-Golgi Network (TGN) it is exposed to low pH. This acidic environment causes a conformational change in the E protein which disassociates it from the prM protein and causes it to form E homodimers. These homodimers lie flat against the viral surface giving the maturing virion a smooth appearance. During this maturation pr peptide is cleaved from the M peptide by the host protease, furin. The M protein then acts as a transmembrane protein under the E-protein shell of the mature virion. The pr peptide stays associated with the E protein until the viral particle is released into the extracellular environment. This pr peptide acts like a cap, covering the hydrophobic fusion loop of the E protein until the viral particle has exited the cell.
The DENV NS3 is a serine protease, as well as an RNA helicase and RTPase/NTPase. The protease domain consists of six β-strands arranged into two β-barrels formed by residues 1–180 of the protein. The catalytic triad (His-51, Asp-75 and Ser-135), is found between these two β-barrels, and its activity is dependent on the presence of the NS2B cofactor. This cofactor wraps around the NS3 protease domain and becomes part of the active site. The remaining NS3 residues (180–618), form the three subdomains of the DENV helicase. A six-stranded parallel β-sheet surrounded by four α-helices make up subdomains I and II, and subdomain III is composed of 4 α-helices surrounded by three shorter α-helices and two antiparallel β-strands.
The DENV NS5 protein is a 900 residue peptide with a methyltransferase domain at its N-terminal end (residues 1–296) and a RNA-dependent RNA polymerase (RdRp) at its C-terminal end (residues 320–900). The methyltransferase domain consists of an α/β/β sandwich flanked by N-and C-terminal subdomains. The DENV RdRp is similar to other RdRps containing palm, finger, and thumb subdomains and a GDD motif for incorporating nucleotides.
The reason that some people suffer from more severe forms of dengue, such as dengue hemorrhagic fever, is multifactorial. Different strains of viruses interacting with people with different immune backgrounds lead to a complex interaction. Among the possible causes are cross-serotypic immune response, through a mechanism known as antibody-dependent enhancement, which happens when a person who has been previously infected with dengue gets infected for the second, third or fourth time. The previous antibodies to the old strain of dengue virus now interfere with the immune response to the current strain, leading paradoxically to more virus entry and uptake.
Immune system interaction
In recent years, many studies have shown that flaviviruses, especially dengue virus has the ability to inhibit the innate immune response during the infection. Indeed, the dengue virus has many nonstructural proteins that allow the inhibition of various mediators of the innate immune system response. These proteins act on two levels :
Inhibition of interferon signaling by blocking signal transducer
NS4B it is a small hydrophobic protein located in association with the endoplasmic reticulum. It may block the phosphorylation of STAT 1 after induction by interferons type I alpha, beta. In fact, the activity of Tyk2 kinase decreases with the dengue virus, so STAT 1 phosphorylation decreases too. Therefore, the innate immune system response may be blocked. Thus there is no production of ISG. NS2A and NS4A cofactor may also take part in the STAT 1 inhibition.
NS5 : the presence of this 105 kDa protein results in inactivation of STAT2 (via the signal transduction of the response to interferon) when it is expressed alone. When NS5 is cleaved with NS4B by a protease (NS2B3) it can degrade STAT2. In fact, after the cleavage of NS5 by the protease, there is an E3 ligase association with STAT2, and the E3 ligase targets STAT2 for the degradation.
Inhibition of the type I interferon response
NS2B3-b protease complex is a proteolytic core consisting of the last 40 amino acids of NS2B and the first 180 amino acids of NS3. Cleavage of the NS2B3 precursor activates the protease complex. This protease complex allows the inhibition of the production of type I interferon by reducing the activity of IFN-beta promoter: studies have shown that NS2B3 protease complex is involved in inhibiting the phosphorylation of IRF3. A recent study shows that the NS2B3 protease complex inhibits (by cleaving) protein MITA which allows the IRF3 activation.
There currently is no human vaccine available. Several vaccines are under development by private and public researchers. Developing a vaccine against the disease is challenging. With five different serotypes of the dengue virus that can cause the disease, the vaccine must immunize against all five types to be effective. Vaccination against only one serotype could possibly lead to severe dengue hemorrhagic shock (DHS) when infected with another serotype due to antibody-dependent enhancement. One vaccine was in phase III trials in 2012 and planning for vaccine usage and effectiveness surveillance had started.
In September 2012, it was announced that one of the vaccines had not done well in clinical trials.
As researchers continue their work, governments should also make efforts in protecting their citizens by providing clean environments to live in, which can be done through developing cleaning teams to keep the cities clean.
- Dennis Normile (25 October 2013). "Surprising New Dengue Virus Throws A Spanner in Disease Control Efforts". Science 342: 415. doi:10.1126/science.342.6157.415.
- Rodenhuis-Zybert IA, Wilschut J, Smit JM (August 2010). "Dengue virus life cycle: viral and host factors modulating infectivity". Cell. Mol. Life Sci. 67 (16): 2773–86. doi:10.1007/s00018-010-0357-z. PMID 20372965.
- WHO (2009). Dengue Guidelines for Diagnosis, Treatment, Prevention and Control. World Health Organization. ISBN 92-4-154787-1.
- Hanley, K.A. and Weaver, S.C. (editors) (2010). Frontiers in Dengue Virus Research. Caister Academic Press. ISBN 978-1-904455-50-9.
- Patil JA, Cherian S, Walimbe AM, et al. (August 2011). "Evolutionary dynamics of the American African genotype of dengue type 1 virus in India (1962–2005)". Infection, Genetics and Evolution 11 (6): 1443–8. doi:10.1016/j.meegid.2011.05.011. PMID 21632029.
- "Dengue virus".
- Holmes, EC; Twiddy, SS (May 2003). "The origin, emergence and evolutionary genetics of dengue virus.". Infection, Genetics and Evolution 3 (1): 19–28. doi:10.1016/s1567-1348(03)00004-2. PMID 12797969.
- Halstead, SB (1988). "Pathogenesis of dengue: challenges to molecular biology.". Science 239 (4839): 476–481. Bibcode:1988Sci...239..476H. doi:10.1126/science.3277268. PMID 3277268. Retrieved 23 February 2013.
- Haddow, AD; Guzman, H; Popov, VL; Wood, TG; Widen, SG; Haddow, AD; Tesh, RB; Weaver, SC (Jun 5, 2013). "First isolation of Aedes flavivirus in the Western Hemisphere and evidence of vertical transmission in the mosquito Aedes (Stegomyia) albopictus (Diptera: Culicidae).". Virology 440 (2): 134–9. doi:10.1016/j.virol.2012.12.008. PMID 23582303.
- Tassaneetrithep B, Burgess TH, Granelli-Piperno A, et al. (April 2003). "DC-SIGN (CD209) mediates dengue virus infection of human dendritic cells". J. Exp. Med. 197 (7): 823–9. doi:10.1084/jem.20021840. PMC 2193896. PMID 12682107.
- Krishnan MN, Sukumaran B, Pal U, et al. (May 2007). "Rab 5 is required for the cellular entry of dengue and West Nile viruses". J. Virol. 81 (9): 4881–5. doi:10.1128/JVI.02210-06. PMC 1900185. PMID 17301152.
- Jindadamrongwech S, Thepparit C, Smith DR (May 2004). "Identification of GRP 78 (BiP) as a liver cell expressed receptor element for dengue virus serotype 2". Arch. Virol. 149 (5): 915–27. doi:10.1007/s00705-003-0263-x. PMID 15098107.
- Miller JL, de Wet BJ, deWet BJ, et al. (February 2008). "The mannose receptor mediates dengue virus infection of macrophages". PLoS Pathog. 4 (2): e17. doi:10.1371/journal.ppat.0040017. PMC 2233670. PMID 18266465.
- Perera R, Kuhn RJ (August 2008). "Structural proteomics of dengue virus". Current Opinion in Microbiology 11 (4): 369–77. doi:10.1016/j.mib.2008.06.004. PMC 2581888. PMID 18644250.
- Dejnirattisai W, Jumnainsong A, Onsirisakul N, et al. (May 2010). "Cross-reacting antibodies enhance dengue virus infection in humans". Science 328 (5979): 745–8. Bibcode:2010Sci...328..745D. doi:10.1126/science.1185181. PMID 20448183.
- Diamond MS (September 2009). "Mechanisms of evasion of the type I interferon antiviral response by flaviviruses". J. Interferon Cytokine Res. 29 (9): 521–30. doi:10.1089/jir.2009.0069. PMID 19694536.
- Jones M, Davidson A, Hibbert L, et al. (May 2005). "Dengue virus inhibits alpha interferon signaling by reducing STAT2 expression". J. Virol. 79 (9): 5414–20. doi:10.1128/JVI.79.9.5414-5420.2005. PMC 1082737. PMID 15827155.
- Ho LJ, Hung LF, Weng CY, et al. (June 2005). "Dengue virus type 2 antagonizes IFN-alpha but not IFN-gamma antiviral effect via down-regulating Tyk2-STAT signaling in the human dendritic cell". Journal of Immunology 174 (12): 8163–72. doi:10.4049/jimmunol.174.12.8163. PMID 15944325.
- Muñoz-Jordan JL, Sánchez-Burgos GG, Laurent-Rolle M, García-Sastre A (November 2003). "Inhibition of interferon signaling by dengue virus". Proc. Natl. Acad. Sci. U.S.A. 100 (24): 14333–8. Bibcode:2003PNAS..10014333M. doi:10.1073/pnas.2335168100. PMC 283592. PMID 14612562.
- Ashour J, Laurent-Rolle M, Shi PY, García-Sastre A (June 2009). "NS5 of dengue virus mediates STAT2 binding and degradation". J. Virol. 83 (11): 5408–18. doi:10.1128/JVI.02188-08. PMC 2681973. PMID 19279106.
- Mazzon M, Jones M, Davidson A, Chain B, Jacobs M (October 2009). "Dengue virus NS5 inhibits interferon-alpha signaling by blocking signal transducer and activator of transcription 2 phosphorylation". J. Infect. Dis. 200 (8): 1261–70. doi:10.1086/605847. PMID 19754307.
- Morrison J, Aguirre S, Fernandez-Sesma A (March 2012). "Innate immunity evasion by dengue virus". Viruses 4 (3): 397–413. doi:10.3390/v4030397. PMC 3347034. PMID 22590678.
- Yusof R, Clum S, Wetzel M, Murthy HM, Padmanabhan R (April 2000). "Purified NS2B/NS3 serine protease of dengue virus type 2 exhibits cofactor NS2B dependence for cleavage of substrates with dibasic amino acids in vitro". J. Biol. Chem. 275 (14): 9963–9. doi:10.1074/jbc.275.14.9963. PMID 10744671.
- Rodriguez-Madoz JR, Belicha-Villanueva A, Bernal-Rubio D, Ashour J, Ayllon J, Fernandez-Sesma A (October 2010). "Inhibition of the type I interferon response in human dendritic cells by dengue virus infection requires a catalytically active NS2B3 complex". J. Virol. 84 (19): 9760–74. doi:10.1128/JVI.01051-10. PMC 2937777. PMID 20660196.
- Yu CY, Chang TH, Liang JJ, et al. (June 2012). "Dengue virus targets the adaptor protein MITA to subvert host innate immunity". In Diamond, Michael S. PLoS Pathog. 8 (6): e1002780. doi:10.1371/journal.ppat.1002780. PMC 3386177. PMID 22761576.
- Vaccine Development, Dengue Vaccine Initiative, November 2012, accessed November 5, 2013
- Preparing for Dengue Vaccine Introduction: Recommendations from the 1st Dengue v2V International Meeting, Joseph Torresi, Roberto Tapia-Conyer, Harold Margolis, PLoS Negl Trop Dis 7(9): e2261. doi:10.1371/journal.pntd.0002261