Dengue and Other Viral Hemorrhagic Fevers

VHFs Overview - Feverish Foes

• Viral Families (all RNA viruses):
  • Flaviviridae (e.g., Dengue, Yellow Fever)
  • Filoviridae (e.g., Ebola, Marburg)
  • Arenaviridae (e.g., Lassa)
  • Bunyaviridae (e.g., CCHF, Hantavirus)
• Transmission:
  • Arthropod-borne (mosquitoes, ticks)
  • Rodent-borne (contact with excreta)
  • Direct contact (infected animals/humans, body fluids)
• Pathogenesis:
  • Endothelial dysfunction → ↑vascular permeability
  • Coagulopathy → bleeding
  • Cytokine storm → systemic inflammation

⭐ Most VHFs are zoonotic, with humans typically being accidental hosts rather than primary reservoirs for the virus (exception: human-to-human transmission in some VHFs like Ebola).

Dengue Deep Dive - Breakbone's Bad Rash

• Virology: Flavivirus (4 serotypes: DENV1-4). Vector: Aedes aegypti, A. albopictus.
• Clinical Phases: Febrile, Critical (plasma leakage), Recovery. See flowchart.
• WHO 2009 Classification:
  • Dengue without warning signs.
  • Dengue with warning signs: 📌 PLEASE M L H (Persistent vomiting, Lethargy/restlessness, Edema/effusion, Abdominal pain/tenderness, Spontaneous bleeding, Enlarged liver >2cm, Mucosal bleed, Hepatomegaly >2cm, Lab: rising HCT concurrent with ↓platelets).
  • Severe Dengue: Severe plasma leakage (shock, respiratory distress), severe bleeding, severe organ involvement (AST/ALT ≥1000 U/L, impaired consciousness, myocarditis).
• Dermatological: Facial flushing, maculopapular rash, petechiae, purpura. Convalescent 'isles of white in a sea of red' rash (Hermann’s rash).

⭐ Tourniquet test: ≥10 petechiae/inch² after 5 min cuff inflation (midway SBP/DBP) indicates capillary fragility; a positive test supports diagnosis but is not specific.

Other VHFs Spotlight - Contagious Cousins

• Chikungunya: Togaviridae (Alphavirus); Aedes mosquito. High fever, severe debilitating polyarthralgia (can be chronic), maculopapular rash. Arthralgia more prominent than Dengue; hemorrhage rare.
• Kyasanur Forest Disease (KFD): Flavivirus; Haemaphysalis ticks (monkeys reservoir). 📌 'Monkey Fever'. Endemic: South India. Biphasic: fever, headache, myalgia, hemorrhage, meningoencephalitis.
• Crimean-Congo Hemorrhagic Fever (CCHF): Nairovirus (Bunyaviridae); Hyalomma ticks. Sudden high fever, myalgia, dizziness, severe hemorrhage (petechiae to GI bleed). Mortality: 30-40%. Ribavirin early.

VHF Dx & Rx - Lab & Lifelines

• Labs: Leukopenia, thrombocytopenia, ↑AST>ALT (Dengue), coagulopathy (↑PT/APTT, ↑FDPs/D-dimer).
• Dengue Dx:
  • NS1 Ag (day 1-7), IgM (day 4-5+), IgG (later/secondary). RT-PCR (day 1-7).
  • Tourniquet test: ≥10 petechiae/inch².
• Other VHF Dx: Specific IgM/IgG ELISA, RT-PCR.
• Rx Principles:
  • Supportive (hydration, paracetamol). AVOID NSAIDs/Aspirin.
  • Severe Dengue: Isotonic crystalloids; platelets if <20,000/µL + bleed or <10,000/µL high risk.
  • Ribavirin: CCHF, Lassa.
• Prevention: Vector control, personal protection, vaccines (Dengvaxia for seropositive 9-45 yrs; KFD).

⭐ In Dengue, AST levels are typically higher than ALT levels (AST>ALT).

High‑Yield Points - ⚡ Biggest Takeaways

• Dengue: "break-bone fever", characteristic rash (islands of white in sea of red), positive Tourniquet test.
• Warning signs: severe abdominal pain, persistent vomiting, mucosal bleed, lethargy, hepatomegaly.
• Severe dengue: plasma leakage (shock, effusions), severe bleeding, organ impairment.
• Labs: thrombocytopenia, leukopenia, hemoconcentration (↑ Hct).
• Other VHFs (e.g., Ebola, Lassa): multi-organ failure, high mortality. Ribavirin for Lassa/CCHF.
• Vector control (Aedes) is key for Dengue prevention and other arboviral VHFs.