Dengue & Dengue Haemorrhagic Fever — SAQ

Stem

A candidate is asked to manage a classic presentation of Dengue & Dengue Haemorrhagic Fever in an exam setting. Use precise definitions, scores, doses, and decision thresholds.

Core knowledge (model answer backbone)

Dengue is an acute mosquito-borne flaviviral illness caused by four antigenically distinct serotypes (DENV-1 to DENV-4), transmitted mainly by the day-biting Aedes aegypti mosquito (also A. albopictus). It is the most important arboviral disease of humans, endemic across the tropics with ~96 million symptomatic cases a year (about 390 million infections). The clinical spectrum runs from undifferentiated fever through classic dengue fever (DF) to dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS) — the latter driven by plasma leakage, thrombocytopenia and bleeding. A secondary infection with a different serotype is markedly more severe through antibody-dependent enhancement (ADE). The illness has three phases — febrile (2-7 days), critical (24-48 h around defervescence) when leakage peaks and shock supervenes, and recovery. Diagnosis rests on NS1 antigen (days 1-5) and IgM ELISA (after day 5). There is no specific antiviral: management is fluid titration — oral fluids and paracetamol in mild disease (AVOID NSAIDs and aspirin); isotonic crystalloid for the leaking patient; bolus resuscitation for shock. With prompt IV fluids, severe-dengue mortality falls below 1%; untreated shock kills within 12-24 hours. Dengvaxia (CYD-TDV) and Qdenga (TAK-003) v

Red flags

• High fever, retro-orbital headache, severe myalgia, rash and thrombocytopenia in the monsoon season - dengue; NS1 antigen (first 5 days), IgM after
• Abdominal pain, persistent vomiting, mucosal bleeding, lethargy, rising haematocrit with falling platelets as fever settles - WARNING SIGNS; admit, start IV fluids
• Cold extremities, narrow pulse pressure (under 20 mmHg), tachycardia, oliguria as fever defervesces - DSS; immediate crystalloid bolus 10-20 mL/kg over 15-20 minutes
• Profound shock, undetectable BP, major bleeding (melaena, haematemesis, intracranial) - severe dengue/DSS; ICU, crystalloid or colloid bolus, transfuse

High-yield structure examiners expect

Cover: Overview & Definition, Classification, Epidemiology & Risk Factors, Pathophysiology, Clinical Presentation, Differential Diagnosis.

Key doses / thresholds (from topic teaching)

• Paracetamol ONLY for fever/pain: adults max 4 g/day, dosing interval not less than 6 hours (WHO); NEVER NSAIDs/aspirin (bleeding risk, Reye syndrome)
• DSS bolus: isotonic crystalloid 10-20 mL/kg over 15-20 min (WHO 1997); WHO-regimen alternative RL 20 mL/kg over 15 min then stepwise 10/7/5/3 mL/kg/h
• Urine output target: at least 0.5 mL/kg/hour
• WHO 1997 grade I-IV; DSS = grades III-IV; managed as WHO 2009 group B/C
• DHF criteria: platelets under 100 x10^9/L + haematocrit rise 20% or more (or fall 20% or more after fluids) + fever 2-7 days + haemorrhagic tendency
• Secondary infection: IgM/IgG OD ratio under 1.2 (or under 1.4 by assay)

Questions

a) Define the condition and give the most important classification or severity framework used in exams. (3 marks)

• Clear one-line definition matching standard teaching.
• Named classification / stages / types with discriminating features.
• One sentence on why classification changes management.

b) Outline pathophysiology in a mechanism chain that explains the main clinical features. (3 marks)

• Initiating insult → intermediate pathway → end-organ effect.
• Link at least two symptoms/signs to mechanism.
• Mention one complication pathway (e.g. shock, perforation, herniation, arrhythmia).

c) List discriminating clinical features and bedside assessment. (3 marks)

• Classic presentation plus one atypical group (elderly, pregnancy, child, immunocompromised).
• Named signs/manoeuvres if relevant.
• What must never be missed on exam/bedside (pregnancy test, airway, glucose, etc.).

d) Investigations with thresholds and one named score if applicable. (3 marks)

• First-line tests and what positive findings mean.
• Gold-standard or definitive investigation when needed.
• Score components reproduced exactly if a named score is standard for this topic.

e) Immediate resuscitation and definitive management with doses where standard. (3 marks)

• ABC / time-critical steps first.
• First-line drug(s) with agent + dose + route (or procedure steps).
• Escalation triggers (theatre, ICU, thrombolysis window, antidote, etc.).
• Disposition and safety-netting.

Marking tips

Full marks require specificity (numbers, names, doses) not generic "give antibiotics/fluids." Regional practice (ICMR / NICE / AHA) may be cited as alternative where relevant.