MBBS Year
2nd Year
Subject
What Is Usually Asked
Virus, serotypes, pathogenesis, laboratory diagnosis
ReferenceAll Years (1st-Final)All UniversitiesDengue
Dengue: Notes, PPT and PYQs for MBBS
Dengue is an acute viral illness caused by the dengue virus and transmitted mainly by the Aedes aegypti mosquito. It ranges from a mild febrile illness to severe dengue with plasma leakage, shock and bleeding. It is examined in Microbiology in 2nd Year, Community Medicine in 3rd Year, and General Medicine and Paediatrics in Final Year.
SME-reviewed. Updated 2026.
Open in GeckoMed for PPT slides and offline notesQuick Summary: What You Need to Know for University Exams
- Dengue is caused by a flavivirus with four serotypes (DENV-1 to DENV-4).
- The main vector is Aedes aegypti, a day-biting mosquito that breeds in clean stored water.
- Secondary infection with a different serotype increases the risk of severe dengue through antibody-dependent enhancement.
- The WHO 2009 classification divides dengue into dengue without warning signs, dengue with warning signs, and severe dengue.
- The illness has three phases: febrile, critical and recovery. The critical phase is when plasma leakage occurs.
- NS1 antigen is useful in the first five days; IgM antibody after day five.
- There is no specific antiviral; management is careful fluid therapy. Aspirin and NSAIDs should be avoided.
Dengue Across MBBS Subjects
| MBBS Year | Subject | What Is Usually Asked |
|---|---|---|
| 2nd Year | Microbiology | Virus, serotypes, pathogenesis, laboratory diagnosis |
| 2nd Year | Pathology | Thrombocytopenia, bleeding, plasma leakage |
| 3rd Year | Community Medicine | Epidemiology, Aedes vector, vector control, national programme |
| Final Year | General Medicine | Clinical phases, warning signs, fluid management |
| Final Year | Paediatrics | Dengue shock syndrome in children |
MBBS Year
2nd Year
Subject
What Is Usually Asked
Thrombocytopenia, bleeding, plasma leakage
MBBS Year
3rd Year
Subject
What Is Usually Asked
Epidemiology, Aedes vector, vector control, national programme
MBBS Year
Final Year
Subject
What Is Usually Asked
Clinical phases, warning signs, fluid management
MBBS Year
Final Year
Subject
What Is Usually Asked
Dengue shock syndrome in children
Definition and Classification
Definition: Dengue is an acute systemic viral infection caused by any of the four dengue virus serotypes, transmitted by Aedes mosquitoes, characterised by fever, headache, myalgia, rash and, in severe cases, plasma leakage, bleeding and organ impairment.
WHO 2009 Classification
| Category | Key Features |
|---|---|
| Dengue without warning signs | Fever with two or more of: nausea or vomiting, rash, aches and pains, positive tourniquet test, leucopenia |
| Dengue with warning signs | Dengue plus any warning sign (see below) |
| Severe dengue | Severe plasma leakage (shock or fluid accumulation with respiratory distress), severe bleeding, or severe organ impairment |
Category
Dengue without warning signs
Key Features
Fever with two or more of: nausea or vomiting, rash, aches and pains, positive tourniquet test, leucopenia
Category
Dengue with warning signs
Key Features
Dengue plus any warning sign (see below)
Category
Severe dengue
Key Features
Severe plasma leakage (shock or fluid accumulation with respiratory distress), severe bleeding, or severe organ impairment
Warning Signs
- Abdominal pain or tenderness
- Persistent vomiting
- Clinical fluid accumulation (ascites, pleural effusion)
- Mucosal bleeding
- Lethargy or restlessness
- Liver enlargement of more than 2 cm
- Rising haematocrit with a rapid fall in platelet count
Older Terms (Still Asked in Exams)
- Dengue haemorrhagic fever (DHF): Fever, bleeding tendency, thrombocytopenia and evidence of plasma leakage
- Dengue shock syndrome (DSS): DHF with circulatory failure
Aetiology and Transmission
| Factor | Details |
|---|---|
| Agent | Dengue virus, a flavivirus with four serotypes (DENV-1, 2, 3, 4) |
| Vector | Aedes aegypti (main), Aedes albopictus |
| Vector habits | Bites during the daytime; breeds in clean, stagnant water in containers, coolers, tyres and flower pots |
| Host | All ages; infection gives lifelong immunity only to the infecting serotype |
| Environment | Urbanisation, water storage, poor waste management, rainy season |
Factor
Agent
Details
Dengue virus, a flavivirus with four serotypes (DENV-1, 2, 3, 4)
Factor
Vector
Details
Aedes aegypti (main), Aedes albopictus
Factor
Vector habits
Details
Bites during the daytime; breeds in clean, stagnant water in containers, coolers, tyres and flower pots
Factor
Host
Details
All ages; infection gives lifelong immunity only to the infecting serotype
Factor
Environment
Details
Urbanisation, water storage, poor waste management, rainy season
Pathophysiology
Flowchart
- An infected Aedes mosquito injects the virus during a bite
- The virus infects dendritic cells, monocytes and macrophages and spreads through the blood
- Immune activation releases cytokines
- Endothelial dysfunction increases capillary permeability
- Plasma leaks into the pleural and peritoneal spaces, causing haemoconcentration
- Loss of intravascular volume leads to shock if not corrected
- Thrombocytopenia, platelet dysfunction and coagulation abnormalities cause bleeding
Antibody-dependent enhancement (ADE): In a second infection with a different serotype, non-neutralising antibodies from the first infection bind the new virus and help it enter immune cells, increasing viral load and the risk of severe dengue.
(Examiner may ask you to draw the pathogenesis flowchart.)
Clinical Features
Phases of Dengue
| Phase | Timing | Key Features |
|---|---|---|
| Febrile | First 2 to 7 days | High fever, headache, retro-orbital pain, severe muscle and joint pain ("breakbone fever"), flushing, rash, positive tourniquet test |
| Critical | Around defervescence, usually lasting 24 to 48 hours | Plasma leakage, rising haematocrit, falling platelets, warning signs, risk of shock and bleeding |
| Recovery | After the critical phase | Reabsorption of leaked fluid, improving appetite, rising platelets, convalescent rash; risk of fluid overload if IV fluids continue unnecessarily |
Phase
Febrile
Timing
First 2 to 7 days
Key Features
High fever, headache, retro-orbital pain, severe muscle and joint pain ("breakbone fever"), flushing, rash, positive tourniquet test
Phase
Critical
Timing
Around defervescence, usually lasting 24 to 48 hours
Key Features
Plasma leakage, rising haematocrit, falling platelets, warning signs, risk of shock and bleeding
Phase
Recovery
Timing
After the critical phase
Key Features
Reabsorption of leaked fluid, improving appetite, rising platelets, convalescent rash; risk of fluid overload if IV fluids continue unnecessarily
Convalescent rash: Classically described as "islands of white in a sea of red."
Tourniquet test: A blood pressure cuff is inflated midway between systolic and diastolic pressure for five minutes; the test is positive if 10 or more petechiae appear per square inch.
Differential Diagnosis
| Condition | Distinguishing Points |
|---|---|
| Chikungunya | Prominent, often long-lasting joint pain |
| Malaria | Periodic fever, splenomegaly, parasites on smear |
| Typhoid | Step-ladder fever, relative bradycardia, positive blood culture |
| Leptospirosis | Exposure to contaminated water, conjunctival suffusion, jaundice and renal involvement |
Condition
Chikungunya
Distinguishing Points
Prominent, often long-lasting joint pain
Condition
Malaria
Distinguishing Points
Periodic fever, splenomegaly, parasites on smear
Condition
Typhoid
Distinguishing Points
Step-ladder fever, relative bradycardia, positive blood culture
Condition
Leptospirosis
Distinguishing Points
Exposure to contaminated water, conjunctival suffusion, jaundice and renal involvement
Diagnosis
| Test | When Useful | Key Points |
|---|---|---|
| NS1 antigen (ELISA or rapid test) | Days 1 to 5 | Detects viral antigen early in illness |
| IgM antibody (ELISA) | After day 5 | Indicates recent infection |
| IgG antibody | Later | High early IgG suggests secondary infection |
| RT-PCR | First few days | Detects viral RNA and identifies the serotype |
| Complete blood count | Daily in admitted patients | Leucopenia, thrombocytopenia, rising haematocrit (a rise of 20% or more suggests plasma leakage) |
| Liver function tests | As needed | Raised transaminases |
| Chest X-ray and ultrasound | Suspected leakage | Pleural effusion, ascites, gall bladder wall thickening |
Test
NS1 antigen (ELISA or rapid test)
When Useful
Days 1 to 5
Key Points
Detects viral antigen early in illness
Test
IgM antibody (ELISA)
When Useful
After day 5
Key Points
Indicates recent infection
Test
IgG antibody
When Useful
Later
Key Points
High early IgG suggests secondary infection
Test
RT-PCR
When Useful
First few days
Key Points
Detects viral RNA and identifies the serotype
Test
Complete blood count
When Useful
Daily in admitted patients
Key Points
Leucopenia, thrombocytopenia, rising haematocrit (a rise of 20% or more suggests plasma leakage)
Test
Liver function tests
When Useful
As needed
Key Points
Raised transaminases
Test
Chest X-ray and ultrasound
When Useful
Suspected leakage
Key Points
Pleural effusion, ascites, gall bladder wall thickening
Management
There is no specific antiviral treatment. Management depends on the phase and severity of illness.
Dengue Without Warning Signs (Can Be Managed at Home)
- Adequate rest and oral fluids
- Paracetamol for fever and pain
- Avoid aspirin, ibuprofen and other NSAIDs, which increase bleeding risk
- Daily review, with instructions to return if warning signs appear
Dengue With Warning Signs (Hospital Admission)
- Intravenous isotonic crystalloids
- Adjust fluid rate according to haematocrit, vital signs and urine output
- Close monitoring through the critical phase
- Reduce fluids gradually as leakage settles
Severe Dengue
- Immediate fluid resuscitation with crystalloid boluses; colloids in refractory shock
- Blood transfusion for significant bleeding or suspected occult bleeding
- Intensive monitoring of haematocrit, blood pressure, urine output and organ function
- Treat complications such as organ failure
Role of Platelet Transfusion
Prophylactic platelet transfusion is not routinely recommended in stable patients. It is considered mainly in significant bleeding or as advised by national guidelines.
Common Management Pitfalls
| Pitfall | Why It Matters |
|---|---|
| Giving NSAIDs or aspirin | Increases bleeding risk |
| Excessive IV fluids in the recovery phase | Causes fluid overload and pulmonary oedema |
| Treating the platelet count alone | Haematocrit and haemodynamic status guide fluid therapy |
| Missing warning signs | Delays admission and increases the risk of shock |
Pitfall
Giving NSAIDs or aspirin
Why It Matters
Increases bleeding risk
Pitfall
Excessive IV fluids in the recovery phase
Why It Matters
Causes fluid overload and pulmonary oedema
Pitfall
Treating the platelet count alone
Why It Matters
Haematocrit and haemodynamic status guide fluid therapy
Pitfall
Missing warning signs
Why It Matters
Delays admission and increases the risk of shock
Complications
- Dengue shock syndrome
- Severe bleeding, including gastrointestinal bleeding
- Acute liver injury
- Myocarditis
- Encephalopathy
- Acute kidney injury
- Fluid overload during recovery
- Multi-organ failure
Prevention and Control (Community Medicine Angle)
| Measure | Examples |
|---|---|
| Source reduction | Remove or cover water containers, empty coolers weekly, dispose of tyres and junk that collect water |
| Larval control | Larvicides such as temephos in water containers |
| Adult mosquito control | Space spraying (fogging) during outbreaks |
| Personal protection | Full-sleeved clothing, repellents, window screens, bed nets during daytime rest |
| Community participation | Awareness drives and regular household checks |
| Surveillance | Case reporting under the national vector-borne disease programme |
Measure
Source reduction
Examples
Remove or cover water containers, empty coolers weekly, dispose of tyres and junk that collect water
Measure
Larval control
Examples
Larvicides such as temephos in water containers
Measure
Adult mosquito control
Examples
Space spraying (fogging) during outbreaks
Measure
Personal protection
Examples
Full-sleeved clothing, repellents, window screens, bed nets during daytime rest
Measure
Community participation
Examples
Awareness drives and regular household checks
Measure
Surveillance
Examples
Case reporting under the national vector-borne disease programme
India: Dengue control falls under the National Centre for Vector Borne Diseases Control (NCVBDC). National Dengue Day is observed on 16 May. Dengue vaccine is not part of India's Universal Immunisation Programme.
Prognosis
Most patients recover fully with early recognition and appropriate fluid management. Deaths occur mainly from delayed recognition of shock, severe bleeding or fluid overload.
Quick Viva Questions
Q: What is the vector of dengue and when does it bite? A: Aedes aegypti, which bites during the daytime.
Q: What does a rising haematocrit indicate in dengue? A: Plasma leakage and haemoconcentration.
Q: Which test is used in the first five days of fever? A: NS1 antigen test.
Q: Why is a second dengue infection more dangerous? A: Antibody-dependent enhancement increases viral entry and the risk of severe dengue.
Q: Which drug is used for fever in dengue? A: Paracetamol; aspirin and other NSAIDs are avoided.
How Dengue Appears in MBBS University Exams
Typical question styles (not attributed to specific papers or years):
- "Discuss the clinical features, laboratory diagnosis and management of dengue fever." (Long essay, General Medicine)
- "Write a short note on dengue haemorrhagic fever and dengue shock syndrome." (Short note)
- "Describe the laboratory diagnosis of dengue." (Short note, Microbiology)
- "Enumerate the warning signs of dengue." (Short answer)
- "Describe the epidemiology and control of dengue in India." (Long essay, Community Medicine)
Frequently Asked Questions
Which test is best for early dengue diagnosis?
The NS1 antigen test is most useful in the first five days of fever. IgM antibody testing is more useful after day five.
Why should NSAIDs be avoided in dengue?
NSAIDs and aspirin impair platelet function and irritate the stomach lining, increasing the risk of bleeding in a disease that already causes thrombocytopenia. Paracetamol is used for fever and pain.
Can I download the dengue PPT for my presentation?
Yes. Use the Download PPT button at the top of this page. The GeckoMed app also gives offline access to the slides and notes.
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