Dengue Fever
Summary
Dengue Fever is an acute viral illness caused by the Dengue virus (Flavivirus family), transmitted by the Aedes aegypti mosquito. There are 4 serotypes (DENV-1, 2, 3, 4). It is endemic in tropical and subtropical regions worldwide, with ~400 million infections/year. Dengue presents with sudden high fever, severe headache (especially retro-orbital), myalgia/arthralgia ("Breakbone Fever"), and a characteristic maculopapular rash ("Islands of white in a sea of red"). The illness progresses through three phases: Febrile -> Critical -> Recovery. The critical phase (around days 3-7) involves plasma leakage, thrombocytopenia, and risk of Dengue Shock Syndrome (DSS) and Dengue Haemorrhagic Fever (DHF). Importantly, second infection with a DIFFERENT serotype increases the risk of severe disease due to Antibody-Dependent Enhancement (ADE). Management is supportive (Fluids, Paracetamol, Monitoring). NSAIDs/Aspirin are contraindicated (Bleeding risk).
Key Facts
- Vector: Aedes aegypti (daytime biting mosquito).
- Serotypes: 4 (DENV-1, 2, 3, 4). Infection with one provides lifelong immunity to that serotype, but increases risk of severe disease on re-infection with a different serotype (ADE).
- Incubation: 4-10 days.
- Phases: Febrile (Days 1-3) -> Critical (Days 3-7 – Plasma Leak) -> Recovery (Days 7-10).
- Classic Features: High fever, Retro-orbital headache, Myalgia ("Breakbone"), Maculopapular rash.
- Warning Signs: Abdominal pain, Persistent vomiting, Lethargy, Bleeding, Rising Haematocrit.
- Treatment: Supportive. Fluids. Paracetamol. NO NSAIDs/Aspirin.
Clinical Pearls
"Breakbone Fever": Severe myalgia and arthralgia are hallmarks of dengue – patients feel like their bones are breaking.
"Islands of White in a Sea of Red": The classic dengue rash spares small islands of normal skin.
"Watch the Haematocrit": Rising Haematocrit (Haemoconcentration) indicates plasma leakage -> Critical phase.
"Second Time is Worse": Heterotypic (Different serotype) re-infection causes severe dengue via ADE.
Why This Matters Clinically
Dengue is expanding globally due to climate change. Early recognition of warning signs and appropriate fluid management during the critical phase prevents mortality. NSAIDs/Aspirin are contraindicated.
Incidence
- Global Burden: ~400 million infections/year. ~100 million symptomatic.
- Distribution: Tropical/Subtropical. SE Asia, Americas, Africa, Western Pacific.
- Expanding Range: Climate change. Urbanisation. Travel.
Vector
| Mosquito | Notes |
|---|---|
| Aedes aegypti | Primary vector. Daytime biter. |
| Aedes albopictus | Secondary vector. Temperate climates. |
Serotypes
| Serotype | Notes |
|---|---|
| DENV-1 | Global. |
| DENV-2 | Associated with more severe disease. |
| DENV-3 | Global. |
| DENV-4 | Less common. |
Mechanism
| Step | Detail |
|---|---|
| Mosquito Bite | Virus inoculated. |
| Initial Replication | In Dendritic cells and Macrophages. |
| Viraemia | Virus in bloodstream -> Febrile phase. |
| Immune Activation | Cytokine storm. |
| Plasma Leakage | Increased capillary permeability -> Haemoconcentration, Hypovolaemia. |
| Thrombocytopenia | Bone marrow suppression. Platelet consumption. |
| Recovery | Fluid reabsorption. |
Antibody-Dependent Enhancement (ADE)
| Concept | Explanation |
|---|---|
| First Infection | Antibodies develop against that serotype. Lifelong immunity to that serotype. |
| Second Infection (Different Serotype) | Cross-reactive, non-neutralising antibodies ENHANCE viral uptake into cells. |
| Result | Higher viraemia. More severe disease. DHF/DSS. |
Capillary Leak Syndrome (Critical Phase)
- Plasma leaks from intravascular to interstitial space.
- Pleural effusion, Ascites.
- Haemoconcentration (Rising Haematocrit).
- Hypovolaemia -> Shock (DSS).
Phases of Illness
| Phase | Timing | Features |
|---|---|---|
| Febrile Phase | Days 1-3 (Up to 7) | High fever (39-40°C), Headache, Retro-orbital pain, Myalgia, Arthralgia, Nausea/Vomiting, Rash. |
| Critical Phase | Days 3-7 (Around Defervescence) | Plasma leakage, Rising Haematocrit, Thrombocytopenia, Warning Signs, Risk of DSS/DHF. |
| Recovery Phase | Days 7-10 | Fluid reabsorption, Improving platelets, Diuresis, Bradycardia. "Convalescent Rash". |
Symptoms (Febrile Phase)
| Symptom | Notes |
|---|---|
| High Fever | Abrupt onset. 39-40°C. Biphasic ("Saddleback"). |
| Retro-Orbital Headache | Pain behind the eyes (Characteristic). |
| Severe Myalgia / Arthralgia | "Breakbone Fever". |
| Nausea / Vomiting | Common. |
| Anorexia | |
| Rash | Maculopapular. "Islands of white in a sea of red". Days 3-5. |
| Bleeding | Mild: Petechiae, Gum bleeding, Epistaxis. |
Warning Signs (Critical Phase)
WARNING SIGNS (Indicates Progression to Severe Dengue) | Warning Sign | Notes | |--------------|-------| | Abdominal Pain (Persistent / Severe) | Plasma leak (Ascites). Liver swelling. | | Persistent Vomiting | Cannot tolerate fluids. | | Lethargy / Restlessness | Altered consciousness. Impending shock. | | Mucosal Bleeding | Gum bleeding, Epistaxis, Haematemesis, Melaena. | | Hepatomegaly (>cm) | Liver involvement. | | Rising Haematocrit + Falling Platelets | Haemoconcentration. | | Pleural Effusion / Ascites | Clinical or Radiological. |
Severe Dengue (DSS / DHF)
| Feature | Notes |
|---|---|
| Dengue Shock Syndrome (DSS) | Severe plasma leak. Hypotension. Narrow Pulse Pressure (<20 mmHg). Cold peripheries. Tachycardia. |
| Dengue Haemorrhagic Fever (DHF) | Plasma leak + Haemorrhage. |
| Severe Organ Impairment | Liver (AST/ALT >000), Myocarditis, Encephalopathy. |
Bedside
| Test | Notes |
|---|---|
| Tourniquet Test (Positive) | >0 petechiae per 2.5cm² after BP cuff inflation. Capillary fragility. |
| Haematocrit | Rising = Haemoconcentration = Plasma leak. |
| Platelet Count | Thrombocytopenia (<100,000 = Warning sign). |
Blood Tests
| Test | Notes |
|---|---|
| FBC | Leucopenia. Thrombocytopenia. Rising Haematocrit. |
| Liver Function Tests | Elevated AST/ALT (AST > ALT typical). |
| Dengue NS1 Antigen | Positive in first 5 days. Rapid diagnostic test. |
| Dengue IgM / IgG | IgM positive from Day 5. IgG rises in secondary infection. |
| Coagulation (PT/APTT) | May be deranged in severe. |
Imaging
| Test | Indication |
|---|---|
| CXR | Pleural effusion (Critical phase). |
| USS Abdomen | Ascites. Gallbladder wall thickening. |
Dengue Classification
| Category | Features |
|---|---|
| Dengue Without Warning Signs | Fever + 2 of: Nausea/Vomiting, Rash, Aches, Leucopenia, Positive Tourniquet. |
| Dengue With Warning Signs | Above + Any Warning Sign. |
| Severe Dengue | Severe Plasma Leak (DSS, Fluid accumulation with respiratory distress), Severe Bleeding, Severe Organ Impairment. |
Principles
- Supportive Care.
- Fluid Management (Critical in Critical Phase).
- Monitor for Warning Signs.
- Avoid NSAIDs / Aspirin.
- Hospital Admission for Warning Signs / Severe Dengue.
Outpatient (Dengue Without Warning Signs)
| Intervention | Detail |
|---|---|
| Oral Rehydration | Encourage fluids. ORS. |
| Paracetamol | For fever and pain. |
| Avoid NSAIDs / Aspirin | Bleeding risk. |
| Daily FBC | Monitor Haematocrit and Platelets. |
| Warning Sign Education | Return immediately if any warning sign develops. |
Inpatient (Warning Signs / Severe Dengue)
| Intervention | Detail |
|---|---|
| IV Fluids | Crystalloid (0.9% Saline). Monitor Haematocrit. Aim to replace plasma loss. |
| If Shock (DSS) | Rapid IV bolus (10-20mL/kg). Colloids if not responding. |
| Blood Products | If significant haemorrhage. Platelets rarely transfused unless active bleeding. |
| Monitor Closely | 4-6 hourly Haematocrit. Urine output. Vital signs. |
Fluid Management in Critical Phase
| Scenario | Action |
|---|---|
| Rising Haematocrit + Stable BP | Increase IV fluids. |
| Stable Haematocrit | Reduce IV fluids. |
| Recovery Phase (Falling Haematocrit) | Reduce/Stop IV fluids to avoid fluid overload. |
| Shock | Bolus. Colloid if refractory. |
What NOT to Do
| Avoid | Reason |
|---|---|
| NSAIDs / Aspirin | Bleeding risk (Thrombocytopenia, Platelet dysfunction). |
| Over-Aggressive Fluids in Recovery | Fluid overload. Pulmonary oedema. |
| Platelet Transfusion (Routinely) | Rarely indicated unless active bleeding. |
| Complication | Notes |
|---|---|
| Dengue Shock Syndrome (DSS) | Hypovolaemic shock from plasma leak. |
| Dengue Haemorrhagic Fever (DHF) | Bleeding diathesis. |
| Hepatic Failure | Elevated AST/ALT. Rare fulminant liver failure. |
| Encephalopathy | Rare. Metabolic or direct viral. |
| Myocarditis | |
| Fluid Overload (Recovery Phase) | From IV fluids during reabsorption phase. |
| Scenario | Mortality |
|---|---|
| Uncomplicated Dengue | <1%. |
| Dengue With Appropriate Fluid Management | ~1%. |
| Untreated DSS | ~10-20%. |
| Treated DSS | <1% (With expert care). |
Predictors of Severe Disease
- Secondary infection (Different serotype).
- DENV-2 serotype.
- Children.
- Delayed presentation.
Vector Control
- Eliminate standing water (Mosquito breeding sites).
- Insecticides. Bed nets (Limited – Aedes bites daytime).
- Personal protection (DEET, Long sleeves).
Vaccination
| Vaccine | Notes |
|---|---|
| Dengvaxia (Sanofi) | Live attenuated. Approved for those with prior dengue infection (Seropositive). Risk of ADE if seronegative. |
| Qdenga (Takeda) | Live attenuated. Broader use potential. |
Key Guidelines
| Guideline | Organisation | Notes |
|---|---|---|
| WHO Guidelines for Dengue | World Health Organization | Global standard. 2009 Classification. |
| PHE/UKHSA Guidance | UK Health Security Agency | Traveller's health. |
Scenario 1:
- Stem: A 30-year-old returns from Thailand with 5 days of high fever, severe headache (especially behind the eyes), and muscle aches. He has a maculopapular rash. What is the most likely diagnosis?
- Answer: Dengue Fever.
Scenario 2:
- Stem: What are the warning signs that indicate progression to severe dengue?
- Answer: Abdominal pain (Persistent/Severe), Persistent vomiting, Lethargy/Restlessness, Mucosal bleeding, Rising Haematocrit + Falling Platelets.
Scenario 3:
- Stem: Why is a second dengue infection with a different serotype more dangerous?
- Answer: Antibody-Dependent Enhancement (ADE). Cross-reactive antibodies enhance viral uptake into macrophages, causing higher viraemia and severe disease.
| Scenario | Urgency | Action |
|---|---|---|
| Dengue Without Warning Signs | Outpatient | Home with fluids. Paracetamol. Daily FBC. Education on Warning Signs. |
| Dengue With Warning Signs | Admit | IV Fluids. Close monitoring. |
| Severe Dengue (Shock/DHF) | Emergency | ICU. Aggressive fluid resuscitation. HDU/ICU care. |
| All Dengue in Pregnancy | Admit | Close monitoring. Fetal risk. |
What is Dengue Fever?
Dengue is a viral infection spread by mosquitoes (Aedes – bites during the day). It causes high fever, severe headache, muscle pain ("Breakbone Fever"), and a rash.
What are the warning signs?
- Severe stomach pain.
- Vomiting that won't stop.
- Bleeding from gums or nose.
- Feeling very tired or restless.
- If you have any of these, go to hospital immediately.
How is it treated?
- Rest and fluids.
- Paracetamol for fever and pain.
- Do NOT take ibuprofen or aspirin (increases bleeding risk).
Key Counselling Points
- Stay Hydrated: "Drink plenty of fluids."
- Paracetamol Only: "Do not take ibuprofen or aspirin."
- Watch for Warning Signs: "Come back immediately if you have severe stomach pain, vomiting, or bleeding."
| Standard | Target |
|---|---|
| NS1 / Dengue serology sent for suspected cases | >0% |
| Haematocrit and Platelets monitored daily | 100% (Inpatients) |
| Warning Signs documented and explained to patient | 100% |
| NSAIDs/Aspirin avoided | 100% |
- Etymology: "Dengue" likely from Swahili "Ka-dinga pepo" (Disease caused by evil spirit).
- First Recorded Outbreaks: 1779-1780 in Asia, Africa, North America (Likely Dengue).
- Virus Isolated: 1943 (WWII, Pacific).
- ADE Described: Halstead (1970s) – Explained severe dengue in secondary infections.
- WHO. Dengue: Guidelines for Diagnosis, Treatment, Prevention and Control. 2009. who.int
- Guzman MG, et al. Dengue. Lancet. 2015. PMID: 25529102
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. If you have fever after travel to a dengue-endemic area, please seek medical attention.