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Dengue - Preventive & Social Medicine (PSM)

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The Dengue Syndrome

1. Asymptomatic (silent infection)
2. Undifferentiated fever (viral syndrome)
3. Classical Dengue Fever (DF) - with or without unusual haemorrhage
4. Dengue Haemorrhagic Fever (DHF) - with plasma leakage; subdivides into DHF non-shock and DHF with shock (Dengue Shock Syndrome - DSS)
5. Expanded dengue syndrome / Isolated organopathy (unusual manifestations)

DF/DHF follows an "iceberg/pyramid" phenomenon - most cases at the base are asymptomatic, with DF, DHF, and DSS forming progressively narrower tiers above.

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Problem Statement / Global Burden

• ~3.9 billion people in 128 countries are at risk of dengue infection
• 390 million infections per year; 96 million manifest clinically
• Reported cases rose from <0.5 million (2010) to 4.2 million (2019)
• ~500,000 DHF hospitalizations per year worldwide; ~90% are children <5 years
• CFR: ~2.5% during epidemics
• Attack rate during outbreaks in non-immune populations: 40-50%, can reach 80-90%
• Regions most affected: South-East Asia and Western Pacific

India

• Endemic in 35 states/UTs
• ~157,996 cases with 253 deaths in 2019; CFR 0.1%
• Seasonal pattern: cases peak after monsoon; southern states and Gujarat have perennial transmission
• All four serotypes isolated; DENV-1 and DENV-2 are currently widespread
• SEAR countries classified into 3 categories:
  • Category A (India, Indonesia, Thailand, Myanmar, etc.) - Major public health problem, hyperendemic with all 4 serotypes
  • Category B (Bhutan, Nepal) - Endemicity uncertain, first outbreaks 2004
  • Category C (DPR Korea) - No evidence of endemicity

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Epidemiological Determinants

A. Agent Factors

B. Host Factors

• Age: In hyperendemic areas, DHF primarily affects children; in primary epidemic areas, all age groups affected
• Immunity: No cross-protection between serotypes; secondary infection increases risk of DHF/DSS (only 2-4% develop severe disease in sequential infections)
• Severity: Depends on serotype sequence of secondary infection; DENV-2 secondary infections associated with greater severity

C. Vector Factors

D. Environmental Factors

• Temperature: Optimum 16-30°C; humidity 60-80%
• Aedes population fluctuates with rainfall and water storage
• Even a 2°C rise in temperature shortens the extrinsic incubation period and increases biting frequency
• Rapid urbanization, poor water management, and deficient sanitation amplify transmission

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Clinical Features

1. Classical Dengue Fever

• Incubation period: 3-14 days (commonly 4-7 days)
• Sudden onset high fever (39-40°C)
• Severe headache, retro-orbital pain (pain on eye movement and pressure), photophobia
• Myalgia and arthralgia ("break-bone fever")
• Biphasic fever curve - remission for a few hours to 2 days
• Rash in 80% cases - appears during remission or 2nd febrile phase
  • Early: diffuse flushing/mottling on face, neck, chest
  • Later: maculopapular or scarlatiniform rash on chest/trunk (3rd-4th day), may spread to extremities; may itch and be followed by desquamation
• Fever lasts ~5 days (rarely >7 days); full recovery usual; CFR exceedingly low

2. Dengue Haemorrhagic Fever (DHF) - Three Phases

• Abrupt onset high fever, facial flushing, headache
• Anorexia, vomiting, epigastric discomfort, right costal tenderness
• Maculopapular (rubelliform) rash less common than in DF
• Positive Tourniquet Test (Rumple-Leede test)

• Fever defervescence
• Plasma leakage - leads to pleural effusion, ascites
• Platelet count drops sharply (≤100,000/mm³)
• Haematocrit rises ≥20% (haemoconcentration) - hallmark of plasma leakage
• Risk of shock if plasma leakage is severe

• Plasma reabsorption
• Risk of fluid overload (pulmonary oedema) if IV fluids given excessively

DHF Grading (WHO)

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Diagnostic Criteria (WHO)

Classical Dengue Fever (Probable Case)

• Headache
• Retro-orbital pain
• Myalgia/arthralgia
• Rash
• Haemorrhagic manifestation
• Low WBC
• Confirmed by serology/virus isolation

DHF Criteria (All 4 must be present):

1. Acute fever of 2-7 days
2. Haemorrhagic manifestations (positive tourniquet test, petechiae/ecchymoses, or bleeding from mucosa/GI/injection sites)
3. Platelet count ≤ 100,000/mm³
4. Evidence of plasma leakage: rising haematocrit ≥20%, pleural effusion, ascites, or hypoproteinaemia

Dengue Shock Syndrome (DSS)

• Tachycardia, cool extremities, delayed capillary refill, weak pulse, lethargy/restlessness
• Pulse pressure ≤ 20 mmHg (e.g., 100/80 mmHg)
• Hypotension: systolic <80 mmHg (age <5 yrs) or 80-90 mmHg (older children/adults)

Confirmed Case

• Virus isolation from serum, CSF, or autopsy sample
• Fourfold or greater rise in IgG (by HI test) or rise in IgM
• Detection of virus/antigen by immunohistochemistry, immunofluorescence, or ELISA
• Detection of viral genome by RT-PCR

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Laboratory Diagnosis

• IgM ELISA detects cases after Day 5 of infection
• NS1 ELISA kits can detect cases from Day 1

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Treatment

Dengue Fever (DF)

• Supportive: adequate rest, fluids, paracetamol for fever
• Avoid aspirin/NSAIDs (risk of bleeding/Reye's syndrome)
• Oral rehydration if tolerating orally

DHF (Grades I & II) - Volume Replacement Algorithm

• Oral fluids first
• If not tolerated: IV crystalloids (Normal Saline, Ringer Lactate)
• Monitor haematocrit every 3-4 hours
• If Hct continues to rise: switch to colloids (Dextran 40/haemaccel)
• If Hct falls and patient improving: reduce IV fluids

DSS (DHF Grades III & IV)

• Immediate IV fluid resuscitation - crystalloid or colloid
• If Hct rising: colloid (Dextran 40/polygeline) at 10-20 ml/kg/hour
• If Hct declining: internal bleeding suspected → fresh whole blood 10 ml/kg/hour
• Oxygen to all patients in shock
• Monitor ABCS: Acidosis, Bleeding, Calcium (Na⁺, K⁺), Sugar

Indications for Red Cell Transfusion

1. Overt blood loss ≥10% total blood volume
2. Refractory shock despite fluids + declining haematocrit/Hb
3. Replacement: 10 ml/kg at a time + coagulogram
4. If fluid overload: give packed cells

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Prevention and Control

1. Vector Control (Primary Strategy)

• Eliminate mosquito breeding places
• Weekly Dry Day - empty/scrub/clean all water containers weekly
• Proper covering of stored water
• Filling/sealing permanent water bodies
• Manage roof tops, porticos, sunshades

• Larviciding: Temephos (Abate) - for stored water
• Adult mosquito control: Malathion fogging/spraying (outbreak measure)
• Pyrethroid-based insecticides for indoor residual spraying

• Larvivorous fish (Gambusia, Poecilia) in ornamental tanks, ponds
• Bacillus thuringiensis israelensis (Bti) - biological larvicide

• Full-sleeved clothing
• Mosquito repellents (creams, liquids, coils, mats)
• Bed nets (especially for sleeping infants/children during daytime)
• Screens on windows and doors

2. Vaccine - CYD-TDV (Dengvaxia - Sanofi Pasteur)

• World's first licensed dengue vaccine (licensed in Mexico, December 2015)
• Live attenuated tetravalent (all 4 serotypes) - chimeric yellow fever-dengue vaccine
• Schedule: 3 doses × 0.5 ml; 6-month intervals
• Route: Subcutaneous
• Age indication: 9-45 years (or 9-60 years depending on license) in endemic areas
• Contraindicated in:
  • Severe allergic reaction to components
  • Congenital/acquired immune deficiency
  • Symptomatic HIV or asymptomatic HIV with immune impairment
  • Pregnant/breastfeeding women
• Note: lower age limit is 9 years (safety concern in children aged 2-5 years in Phase 3 trials)
• Storage: 2-8°C; shelf life 36 months; discard reconstituted vaccine within 6 hours

3. Other Measures

• Isolation of patient under bed nets during first few days of illness (prevents further mosquito bites and transmission)
• Health education on Do's and Don'ts
• Sentinel surveillance hospitals (521 identified by GOI) with lab support
• 14 Apex Referral Laboratories for advanced diagnosis
• IgM capture ELISA kits supplied free by National Institute of Virology, Pune

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WHO Global Strategy for Dengue Prevention and Control (2012-2020)

1. Diagnosis and case management
2. Integrated surveillance and outbreak preparedness
3. Sustainable vector control
4. Implementation of future vaccine tools
5. Basic operational and implementation research

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India's National Programme / GOI Steps

• Monitoring through reports from state health authorities
• Mid-term plan (2011) with components:
  • (a) Surveillance (disease + entomological)
  • (b) Case management (lab diagnosis + clinical management)
  • (c) Vector management (environmental + chemical + personal protection + legislation)
  • (d) Outbreak response (epidemic preparedness + media management)
  • (e) Capacity building (training + HR strengthening)
  • (f) Operational research
• Contingency plan for dengue outbreaks sent to all states since 1996 Delhi outbreak

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High-Yield PSM Points (Exam Focus)

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