Dengue Fever

1. Definition

Dengue fever is an acute, mosquito-borne viral illness caused by the Dengue virus (DENV), a flavivirus with four distinct serotypes (DENV-1 to DENV-4). It ranges from a mild, self-limiting febrile illness to severe, potentially fatal disease characterized by plasma leakage, hemorrhage, and organ dysfunction.

2. Causes

Etiologic agent: Dengue virus (DENV), RNA virus, genus Flavivirus
Vector: Primarily transmitted by Aedes aegypti and Aedes albopictus mosquitoes

3. Risk Factors

Risk Factor	Details
Geographic location	Tropical/subtropical regions (Southeast Asia, South America, etc.)
Seasonality	Rainy seasons when mosquito breeding increases
Prior infection	Secondary infection with different DENV serotype increases risk of severe disease
Age	Children and elderly more prone to complications
Comorbidities	Diabetes, asthma, obesity
Living conditions	Urban crowding, poor sanitation, stagnant water

4. Types / Classifications

WHO 2009 Classification:

Category	Description
Dengue without warning signs	Fever + 2 of: nausea, rash, aches, leukopenia, positive tourniquet test
Dengue with warning signs	Abdominal pain, persistent vomiting, fluid accumulation, mucosal bleeding, lethargy, hepatomegaly, rising hematocrit with falling platelets
Severe dengue	Severe plasma leakage (shock/respiratory distress), severe bleeding, severe organ involvement (ALT/AST > 1000, encephalitis, myocarditis)

5. Pathogenesis

Primary infection induces life-long immunity to that serotype but only temporary cross-immunity to others.
Secondary infection with a different serotype increases risk of antibody-dependent enhancement (ADE), leading to:
- Increased viral replication
- Cytokine storm
- Capillary permeability → plasma leakage
- Thrombocytopenia and coagulopathy → hemorrhage

6. Clinical Presentation

Symptoms (3 Phases):

Febrile Phase (2–7 days)
- High-grade fever
- Headache (retro-orbital pain)
- Myalgia, arthralgia ("breakbone fever")
- Rash (maculopapular or petechial)
- Nausea, vomiting
Critical Phase (24–48 hours)
- Defervescence (fever subsides)
- Warning signs: abdominal pain, persistent vomiting, mucosal bleeding, fluid accumulation (ascites, pleural effusion), lethargy
- Risk of shock and bleeding
Recovery Phase
- Resorption of fluids
- Rash (desquamation or "islands of white in sea of red")
- Diuresis

Physical Examination Findings:

Flushed skin
Positive tourniquet test (petechial bleeding after BP cuff inflation)
Hepatomegaly
Signs of dehydration or shock (in severe cases)
Bleeding: epistaxis, gum bleeding, GI bleeding

7. Organ & System Complications

System	Complications
Hematologic	Thrombocytopenia, DIC, bleeding
Cardiovascular	Dengue shock syndrome (hypovolemic shock)
Hepatic	Transaminitis, acute liver failure
Neurological	Encephalitis, seizures, intracranial bleeding
Respiratory	Pleural effusion, ARDS
Renal	Acute kidney injury (in severe cases)

8. Diagnostic Investigations

Test	Purpose	Timing
NS1 antigen	Detects viral antigen early	Day 1–5 of illness
RT-PCR for DENV RNA	Confirms serotype, early detection	Day 1–5
IgM/IgG ELISA	Serology for recent/past infection	IgM (from Day 5), IgG (rises after Day 7)
CBC	Thrombocytopenia, leukopenia, hemoconcentration	Throughout
LFTs	Transaminase elevation	If hepatopathy suspected
Chest X-ray / Ultrasound	Pleural effusion, ascites (plasma leakage)	If warning signs present

9. Other Relevant Investigations

Coagulation profile: PT, aPTT (if bleeding suspected)
Serum electrolytes: for fluid management
ABG: in severe disease with shock/ARDS
Lactate: marker of tissue perfusion
Urinalysis: hematuria or proteinuria in severe cases

10. Treatment

Curative/Definitive:

No antiviral cure available
Supportive management is the mainstay

Empirical:

Empirical supportive therapy based on clinical suspicion in endemic regions, even before confirmation

Supportive:

Fluid management: guided by hematocrit and clinical signs
- Oral rehydration in mild cases
- IV fluids (crystalloids) for warning signs or shock
Paracetamol for fever
Avoid NSAIDs/aspirin (bleeding risk)

Palliative:

Symptom control in patients with severe organ failure not responding to treatment

11. Long-Term Effects / Complications of Treatment

Clinical:

Treatment	Potential Long-Term Complication	Monitoring Investigation
IV fluid resuscitation	Fluid overload, pulmonary edema	Daily weight, chest X-ray, SpO₂
Transfusions	Alloimmunization, volume overload	CBC, vital signs monitoring
Hepatic injury	Chronic transaminitis (rare)	LFTs periodically

Monitoring:

Platelet count: daily or more frequently if declining
Hematocrit: rising HCT suggests plasma leakage
Renal and liver function: if involved
Oxygenation and perfusion status in severe cases

12. Surveillance for the Disease

Public health reporting: mandatory in many countries
Vector control programs: larvicide, insecticide, community sanitation
Outbreak monitoring: syndromic surveillance and lab reporting
Post-infection follow-up (if severe dengue): organ function (renal, hepatic), CBC

References

WHO Dengue Guidelines, 2009
CDC Dengue Clinical Management
UpToDate: Clinical manifestations and diagnosis of dengue