Question
Dengue hemorrhage fever
Answer
Dengue haemorrhagic fever (DHF) is a severe form of dengue virus infection (a flavivirus, transmitted by Aedes aegypti/albopictus mosquitoes), characterized by increased vascular permeability, thrombocytopenia, and haemorrhagic manifestations — distinct from, and more severe than, classical (uncomplicated) dengue fever.
Pathogenesis: DHF is classically associated with secondary infection by a different dengue serotype (of the four antigenically related but distinct serotypes, DENV-1 to DENV-4) in a person previously infected with a different serotype. This is explained by Antibody-Dependent Enhancement (ADE): pre-existing, non-neutralizing (cross-reactive but sub-protective) antibody from the first infection binds the new infecting serotype without neutralizing it, but the antibody-virus complex is then taken up more efficiently by Fc-receptor-bearing cells (monocytes/macrophages), paradoxically enhancing viral entry and replication. This drives a heightened immune/cytokine response (“cytokine storm” — TNF-α and other mediators), which increases capillary permeability, causing plasma leakage into extravascular spaces, along with complement activation and bone marrow suppression contributing to thrombocytopenia.
Clinical/laboratory criteria for DHF (WHO classical criteria):
- Fever.
- Haemorrhagic tendency (positive tourniquet test, petechiae, or spontaneous bleeding).
- Thrombocytopenia (≤100,000/μL).
- Evidence of plasma leakage — a rise in haematocrit (≥20% from baseline), pleural effusion, ascites, or hypoproteinaemia.
Dengue Shock Syndrome (DSS) is the most severe form, occurring when plasma leakage is severe enough to cause circulatory failure/hypotensive shock — a life-threatening medical emergency.
Laboratory diagnosis: NS1 antigen detection (positive in the first few days of illness, before antibody develops); IgM/IgG ELISA (IgM from about day 5, indicating recent infection; IgG rise pattern helps distinguish primary from secondary infection); RT-PCR for viral RNA in the early viraemic phase; full blood count showing thrombocytopenia and rising haematocrit (haemoconcentration).
Management: primarily supportive — careful fluid management (avoiding both under- and over-resuscitation, since capillary leak makes fluid balance critical), monitoring of haematocrit/platelet count/vital signs, and avoiding NSAIDs/aspirin (bleeding risk); no specific antiviral treatment is available.