VHF Flashcards
(13 cards)
What are VHF?
Viral Haemorrhagic Fevers (VHF): Overview
Definition
VHF refers to a group of severe, multisystem febrile illnesses caused by enveloped RNA viruses from four distinct families which are? :
- Arenaviridae
- Filoviridae
- Bunyaviridae
- Flaviviridae
What are the key characteristics of VHF?
Key Characteristics:
- All are RNA viruses with a lipid envelope
- Mostly zoonotic—humans are accidental hosts
- Transmitted by mammalian reservoirs or arthropod vectors
- Outbreaks are sporadic, often linked to ecological changes
- No specific treatment or vaccine for most types
- Virus survival depends on the presence of natural hosts in a defined geography
What’s the Classification of VHFs
Family | Virus | Genome | Reservoir/Vector
| Arenaviridae | Lassa fever | ss(-) RNA | Mastomys natalensis (multimammate rat) |
| | Junin | ss(-) RNA | Calomys musculinus
| | Machupo | ss(-) RNA | Calomys callosus
| Filoviridae | Ebola | ss(-) RNA | Pteropodidae fruit bats |
| | Marburg | ss(-) RNA | Pteropodidae fruit bats
| Flaviviridae | Yellow fever | ss(+) RNA | Aedes aegypti (mosquito) |
| | Dengue | ss(+) RNA | Aedes spp.
| | Kyasanur Forest | ss(+) RNA | Ticks |
| Bunyaviridae | Rift Valley fever | ss(-) RNA | Aedes mosquitoes
| | Crimean-Congo | ss(-) RNA | Hyalomma spp. (tick)
| | Hantavirus | ss(-) RNA | Rodents (e.g., deer mice)
What’s the mode of Transmission of VHF Viruses?
Primary transmission (from reservoirs):
- Rodent excreta (urine, feces, saliva): e.g. Lassa fever, Hantavirus
- Arthropod bites:
- Mosquitoes: Yellow fever, Rift Valley fever
- Ticks: Crimean-Congo hemorrhagic fever, Kyasanur Forest disease
Secondary (person-to-person):
- Direct contact with blood/body fluids from infected persons:
- Seen in Ebola, Marburg, Lassa, and CCHF
- Healthcare settings or burial rituals without protective measures
What’s the Pathophysiology of VHFs
1. Immunopathogenesis (especially in Dengue):
- Overactive immune response causes plasma leakage, shock, and organ damage
2. Coagulopathy and DIC:
- Due to:
- Liver damage (impaired clotting factor production)
- Bone marrow suppression (↓ platelets)
- Consumptive coagulopathy (massive clotting, then bleeding)
3. Increased vascular permeability:
- Capillary leakage leads to hypotension, shock, and edema
4. Multisystem involvement:
- Hemorrhage—usually mild but reflects thrombocytopenia and small vessel fragility
- Widespread endothelial damage disrupts homeostasis
What are the Symptoms of VHF
Early signs:
- Sudden fever
- Fatigue
- Dizziness
- Myalgia
- Weakness
Severe illness:
- Bleeding: under skin, from mucous membranes, orifices
- Shock: due to plasma loss
- Neurological symptoms: confusion, coma, seizures
- Renal failure
Pathophysiology of Viral Hemorrhagic Fevers (VHFs)
VHFs cause disease through immune dysregulation, coagulopathy, and vascular injury, leading to multisystem failure.
1. Viral Entry and Immune Evasion
- Primary infection targets macrophages, dendritic cells, and endothelial cells.
- These viruses suppress early interferon responses, allowing rapid viral replication.
Why it matters:
- Delayed immune response allows viral spread to multiple organs.
- Patients often present late with widespread viremia.
2. Cytokine Storm (Hyperinflammation)
- Infected immune cells release massive amounts of proinflammatory cytokines (e.g. IL-6, TNF-α).
- This leads to systemic inflammation and endothelial activation.
Why it matters:
- Causes fever, hypotension, capillary leak, and sets the stage for shock.
- Resembles sepsis—initial supportive care overlaps.
3. Endothelial Dysfunction and Vascular Leak
- Cytokines and direct viral damage disrupt endothelial integrity.
- Tight junctions loosen ➡️ plasma leaks into tissues.
Why it matters:
- Hemoconcentration, hypovolemia, and shock develop.
- Patients may have edema, pleural effusion, or ascites.
4. Coagulopathy and DIC
- Liver dysfunction ➡️ ⬇️clotting factors
- Bone marrow suppression ➡️thrombocytopenia
- Cytokine storm activates coagulation ➡️consumptive coagulopathy (DIC)
Why it matters:
- Bleeding from gums, nose, GI tract, and injection sites
- Bleeding isn’t always massive, but often signals severe disease
5. Multiorgan Failure
- Virus reaches liver, kidneys, lungs, brain
- Hepatic necrosis ➡️ ⬆️ AST/ALT
- Acute tubular necrosis ➡️ oliguria or renal failure
- Encephalitis or cerebral edema ➡️seizures, coma
Why it matters:
- Explains the shock, confusion, renal shutdown seen in late-stage VHF
- AST > ALT is common in Lassa and Ebola (suggests muscle + liver injury)
Summary: What You See = What’s Happening
Clinical Feature | Underlying Mechanism |
| ——————– | ————————— |
| Fever | Cytokine release |
| Bleeding | DIC + thrombocytopenia |
| Hypotension/shock | Capillary leak |
| Confusion/seizures | CNS invasion, hypoperfusion |
| Oliguria | ATN from shock/cytokines |
| ↑ AST, ALT | Liver cell necrosis |
*Laboratory Diagnosis of VHFs**
Specimens
-
Blood, tissues, and body fluids
➡️ Source of virus, antibodies, antigens, and genetic material
What are the Diagnostic Methods for VHF?
- Serology (IgM/IgG ELISA)
➡️ Detects immune response; useful in later stages or post-recovery
- Antigen detection (ELISA)
➡️ For early detection in acute cases
- RT-PCR (Nucleic acid amplification)
➡️ Rapid, sensitive test; confirms active infection
- Virus isolation (BSL-4 labs only)
➡️ Gold standard but slow and risky
- Electron microscopy
➡️ Useful for filoviruses (e.g., Ebola, Marburg) in research settings
Routine Lab Findings (Support Diagnosis & Monitor Severity)
Test | Finding | Why it matters |
| ——————- | ————————– | —————————————————————————– |
| WBC count | ↓ (especially lymphocytes) | Immunosuppression |
| Platelets | ↓ | Risk of bleeding (thrombocytopenia) |
| AST/ALT | ↑ | Liver damage, especially in Ebola |
| PT/PTT | ↑ | Coagulopathy/DIC |
| Hematocrit | ↑ | Hemoconcentration from plasma loss |
| Urea/Creatinine | ↑ | Renal impairment or dehydration |
| Bleeding time | Prolonged | Platelet or clotting factor issues |
| Urinalysis | Proteinuria, hematuria | Reflects systemic endothelial injury, especially in Lassa, Marburg, Ebola |
What are the Management for VHF
1. Supportive Care is the Mainstay
- Fluid resuscitation
➡️ Prevent hypovolemic shock from capillary leak
- Renal support (e.g., dialysis)
➡️ Needed in oliguric or nephrotoxic states
- Ventilator support
➡️ For respiratory distress, pulmonary edema, or CNS compromise
2. Antiviral Therapy
- Ribavirin
➡️ Only effective in Lassa fever if started early
3. Infection Prevention and Control
- Standard precautions
➡️ Hand hygiene, PPE
- Transmission-based precautions
➡️ Airborne, droplet, and contact depending on virus
- BSL-4 containment
➡️ Required for virus isolation and handling high-risk pathogens
And vaccination?
4. Vaccination
- Available for some VHFs (e.g., Ervebo for Ebola Zaire)
- Others still in development or limited to outbreak use
