Dengue Literature Review

Dengue Pathophysiology

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Dengue Pathophysiology

Overview

Dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS) are defined by three interacting pathological phenomena: (1) increased vascular permeability causing plasma leakage, (2) thrombocytopaenia with impaired platelet function, and (3) coagulopathy with altered haemostasis. These occur in a coordinated, time-locked pattern — emerging during the febrile phase, peaking at defervescence, and typically resolving within 24–36 hours in non-fatal cases. Understanding the molecular drivers of each phenomenon is essential to developing targeted therapies, vaccines, and prognostic tools.

Key Points from Literature

Vascular Permeability

  • The cardinal feature of DHF/DSS; defined by plasma leakage into serous cavities (pleural effusion, ascites) and into the interstitial space
  • Endothelial cell death and direct viral infection of endothelium do not appear to be the primary mechanism: patients recovering from DHF regain normal endothelial function rapidly, implying a reversible soluble mediator rather than structural damage (see Guzman2016 - Dengue Infection)
  • Onset at defervescence, not during peak viraemia — suggesting vascular permeability results from factors that accumulate throughout the febrile phase and surpass a threshold at fever resolution
  • NS1 as a direct trigger: sNS1 activates TLR4 on myeloid cells → pro-inflammatory cytokines; separately, sNS1 disrupts endothelial monolayer integrity in vitro and in vivo; DENV NS1-induced TLR4 signalling is a proposed central mechanism for barrier dysfunction (see Guzman2016 - Dengue Infection, NS1 Protein)
  • APTT as strongest vascular permeability correlate: APTT values (measuring coagulation activation time) are the strongest laboratory correlate of vascular permeability in dengue patients — linking coagulopathy and plasma leakage mechanistically (see Guzman2016 - Dengue Infection)
  • Anti-NS1 autoantibodies additionally induce endothelial apoptosis (NO→p53/Bax/caspase-3 pathway) and NF-κB inflammatory activation (IL-6, IL-8, MCP-1; ICAM-1 upregulation) — a distinct antibody-mediated vascular damage pathway (see NS1 Molecular Mimicry in Dengue)

Thrombocytopaenia

  • Two concurrent mechanisms:
    1. Bone marrow suppression: early febrile phase; suppression of all blood cell lineages; proposed to be mediated by IFN-β (by analogy with lymphocytic choriomeningitis virus in animal models); megakaryocyte arrest persists until near the end of the febrile period
    2. Peripheral platelet destruction: immune-mediated; anti-NS1 IgM autoantibodies cause complement-mediated platelet lysis (see NS1 Molecular Mimicry in Dengue); anti-NS1 antibodies inhibit ADP-induced platelet aggregation via PDI inhibition on the platelet surface (see NS1 Protein)
  • Platelet counts can fall to 5,000/ml (normal ~200,000/ml) at nadir
  • Thrombocytopaenia is common across infectious diseases generally; it is the combination of thrombocytopaenia with vascular permeability that is distinctive of DHF/DSS
  • Platelet count is NOT a reliable predictor of bleeding severity in dengue; risk factors for severe haemorrhage are duration of shock and low-to-normal haematocrit at shock onset (see Guzman2016 - Dengue Infection) (see also Guzman2016 - Dengue Infection)

Coagulopathy

  • Characterised by prolonged APTT (activated partial thromboplastin time), reduced fibrinogen, and reduced anticoagulant protein concentrations
  • Classic disseminated intravascular coagulation (DIC) is debated: procoagulant marker elevation is present but usually mild; anticoagulant protein reduction is more prominent
  • NS1-thrombin binding: sNS1 binds thrombin in vivo forming NS1-thrombin complexes; rNS1 inhibits prothrombin activation and prolongs APTT in human platelet-deficient plasma (see Guzman2016 - Dengue Infection)
  • E protein WGNGCG motif: E protein aa 101–106 homologous to coagulation factors (XI, X, IX, VII, thrombin, plasminogen, tPA); anti-E antibodies inhibit plasmin activity (see NS1 Molecular Mimicry in Dengue, E Protein)
  • Glycocalyx shedding: NS1 may shed heparan sulfate/chondroitin sulfate from the endothelial glycocalyx → anticoagulant molecules enter circulation → contributes to coagulopathy (see Guzman2016 - Dengue Infection)
  • Most coagulopathy is minor and self-limiting; major haemorrhage is usually a complication of prolonged shock, not a primary dengue effect
  • The APTT-vascular permeability correlation raises the possibility that coagulation interference is proximal to, not merely co-incident with, plasma leakage

Complement Activation

  • Complement system activated to control DENV infection but its activation contributes to pathogenesis
  • Secondary infection: classical complement pathway activation via circulating immune complexes; levels of C3a/C5a elevated; temporal correlation with fibrinogen and thrombocytopaenia changes
  • Primary infant infection: alternative complement pathway activated; NS1 may directly activate complement by the alternative pathway
  • Activated complement interacts with the coagulation system, amplifying both coagulopathy and vascular inflammation (see Guzman2016 - Dengue Infection)

Liver Involvement

  • Hepatomegaly in 55% of DHF cases vs. 18% of DF cases (P<0.01); significantly more common in severe disease
  • Mechanisms: (1) generalised oedema from vascular permeability; (2) inflammatory response to hepatocyte infection by DENVs
  • Histopathology: Councilman bodies (apoptotic DENV-infected hepatocytes engulfed by Kupffer cells) — the same histological finding as in yellow fever (another flavivirus); almost no cellular inflammatory infiltrate in fatal cases, suggesting apoptosis rather than inflammatory hepatocyte death
  • AST/ALT elevated in 60–90% of children with DHF; 7–10% have levels >10× upper limit of normal
  • Jaundice is rare despite hepatomegaly; gamma-glutamyl transpeptidase elevated in 83% of cases
  • Post-dengue liver enzyme elevation may persist for months; anti-NS1 hepatitis-like effects in mouse models (see Lin2006 - Autoimmune Pathogenesis in Dengue Virus Infection) (see Guzman2016 - Dengue Infection)

Contradictions & Debates

  • Cause of vascular permeability: Multiple competing models exist — NS1-TLR4, cytokine storm (T cell-mediated), immune complex complement activation, anti-NS1 autoantibody endothelial damage — none fully accounts for all observations. The paper itself notes that none of the existing explanations can account for why infants with no prior infection develop severe dengue.
  • DIC vs non-DIC: The haemostatic profile of DHF resembles but does not fully meet diagnostic criteria for classic DIC; some researchers distinguish dengue coagulopathy as mechanistically distinct.
  • NS1 as mediator vs. marker: sNS1 levels correlate with severity, NS1 can cause endothelial disruption in vitro, and NS1-thrombin binding has been demonstrated in vivo — but whether NS1 is the primary driver of vascular permeability or a secondary marker of disease severity remains debated.

Sources

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