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.
| Feature | Dengue | Chikungunya | KFD (Monkey Fever) | CCHF |
|---|---|---|---|---|
| Vector | Aedes mosquito | Aedes mosquito | Haemaphysalis ticks | Hyalomma ticks |
| Virus Family | Flaviviridae | Togaviridae | Flaviviridae | Bunyaviridae (Nairovirus) |
| Key Clinical | Fever, rash, myalgia, arthralgia, leukopenia | High fever, severe polyarthralgia, rash | Biphasic fever, myalgia, hemorrhage, neuro sx | Sudden fever, myalgia, severe hemorrhage |
| Hemorrhage | Variable, can be severe | Rare | Common | Severe, hallmark |
| Mortality | <1% (severe: 2-5%) | Low | 3-10% | 30-40% |
| India Specifics | Widespread | Widespread | Karnataka, S. India | Gujarat, Rajasthan |
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.
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