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PE31.13 | Vector Borne Fever — SDL Guide (Part 2)

Complications

The complications of vector-borne fevers are each driven by the specific pathophysiological mechanism of the underlying disease — plasma leakage in dengue, microvascular obstruction and haemolysis in falciparum malaria, and perivasculitis in scrub typhus. Recognising these complications early and responding with the correct intervention is the critical skill that separates outcomes in a severe case from those in an uncomplicated one. Missing warning signs in dengue, failing to check blood glucose in malaria, or delaying doxycycline in scrub typhus myocarditis can convert a treatable illness into a fatal one. The complications described below are primarily for P. falciparum malaria and dengue, as these carry the highest mortality among children in India.

Severe dengue (WHO 2009 classification):
Severe dengue is defined by any of three criteria:
1. Severe plasma leakage causing dengue shock syndrome (DSS) or fluid accumulation with respiratory distress (pleural effusion, ascites)
2. Severe bleeding — clinically significant haemorrhage (haematemesis, melaena, vaginal bleeding, intracranial haemorrhage)
3. Severe organ impairment — liver (AST/ALT >1000 IU/L), CNS (impaired consciousness, encephalitis), kidneys, or myocarditis

Dengue shock syndrome occurs as plasma leakage reduces circulating volume, causing: narrow pulse pressure (<20 mmHg), hypotension, cold peripheries, and impaired consciousness. If uncorrected, hypovolaemic shock progresses rapidly.

Severe (complicated) falciparum malaria:
- Cerebral malaria: altered consciousness (Glasgow Coma Scale <15 in adults, Blantyre Coma Scale <2 in children), seizures, coma; results from cytoadherence of infected RBCs blocking cerebral microvasculature + cerebral oedema; mortality 15–20% even with treatment
- Severe anaemia: Hb <5 g/dL from haemolysis + bone marrow suppression; highest risk in young children with repeated infections
- Hypoglycaemia: <2.2 mmol/L; from increased glucose consumption by parasite + insulin release stimulated by quinine (if used); may present as convulsions or altered consciousness
- Respiratory distress: metabolic acidosis (lactic acid from impaired tissue perfusion), pulmonary oedema
- Acute kidney injury: haemoglobinuria ('blackwater fever' from massive intravascular haemolysis) + renal tubular damage
- Hyperparasitaemia: >5% of RBCs parasitised — sign of overwhelming infection

Malaria in special situations:
- P. vivax: vivax malaria was considered 'benign' but severe vivax malaria (cerebral, respiratory distress, severe anaemia) is now well-documented in Indian children
- Pregnancy and neonatal malaria: malaria in pregnancy causes placental insufficiency, low birth weight

Scrub typhus complications:
- Myocarditis and cardiac arrhythmia — from Orientia vasculitis of coronary vessels
- Meningitis and meningoencephalitis — from CNS vasculitis
- ARDS — alveolar capillary endothelial damage
- Hepatitis and acute kidney injury in severe cases
- Complications respond rapidly to doxycycline if started before multi-organ failure

Chikungunya complications: Post-infectious arthritis (weeks to months); rare neurological complications (encephalitis, Guillain-Barré) in severe cases.

Management and Prevention

Management of vector-borne fevers requires disease-specific treatment protocols — there is no single 'febrile illness' treatment algorithm that fits all four diseases. The guiding principle for each is: treat the underlying pathophysiological mechanism, avoid drugs that worsen the specific disease mechanism (aspirin in dengue; primaquine without G6PD testing in malaria), and escalate to hospital care at the first sign of complication or clinical deterioration. Each disease has a different treatment logic: dengue requires fluid management calibrated to the leakage-reabsorption cycle rather than a fixed rate; malaria requires species identification before antibiotic selection; and scrub typhus responds dramatically to doxycycline — so rapidly that treatment response becomes a confirmatory diagnostic test in itself. Across all four diseases, the safety principles are as important as the treatment principles: the harm from aspirin in dengue, from primaquine in G6PD deficiency, and from missing the critical phase of dengue shock is as preventable as the disease itself through correct clinical decision-making.

Dengue management — guided by clinical phase and warning signs:

Dengue without warning signs (outpatient management):
- Adequate oral hydration with ORS or fruit juice (6–7 glasses per day for adults; weight-based for children)
- Paracetamol (15 mg/kg/dose, max 4 doses/day) for fever — DO NOT EXCEED recommended dose (hepatotoxicity risk when liver is already stressed by dengue)
- Avoid aspirin, ibuprofen, other NSAIDs — platelet inhibition + gastric bleeding risk
- Avoid IM injections — haematoma formation risk
- Review daily for warning signs; instruct parents on warning sign recognition
- Monitor blood counts (haematocrit, platelets) every 24–48 hours

Dengue with warning signs (admit for monitoring):
- IV crystalloid (0.9% NaCl or Ringer's lactate): 5–10 mL/kg over 1 hour, then reassess and titrate
- Monitor haematocrit every 4–6 hours; urine output (aim >0.5 mL/kg/hour)
- Reduce IV fluid rate as haematocrit falls (plasma leakage phase ends with recovery)
- Platelet transfusion: only if platelet count <20,000/µL AND active significant bleeding; do NOT transfuse prophylactically for low count alone
- Close monitoring for dengue shock (pulse pressure <20 mmHg → immediate fluid bolus)

Severe dengue (ICU level):
- IV fluid resuscitation for shock; careful fluid management thereafter (excess fluid causes pulmonary oedema once plasma reabsorbs)
- Treat underlying organ dysfunction

Malaria management — by species and severity:

P. falciparum (uncomplicated):
- Artemisinin-based Combination Therapy (ACT): first-line per India's NVBDCP
- Artemether-lumefantrine: weight-based dosing for 3 days (preferred in children)
- Artesunate + amodiaquine: alternative ACT
- ACT achieves the fastest parasite clearance of any antimalarial

P. falciparum (severe/complicated — cerebral malaria, hyperparasitaemia, respiratory distress):
- IV artesunate: 2.4 mg/kg IV at 0, 12, 24 hours, then daily — drug of choice for severe falciparum malaria
- Switch to oral ACT when the child can take oral medication
- Adjunctive: IV dextrose for hypoglycaemia; anticonvulsants for seizures; blood transfusion for severe anaemia (Hb <5 g/dL with respiratory distress)

P. vivax (uncomplicated):
- Chloroquine: 10 mg/kg on day 1, 10 mg/kg on day 2, 5 mg/kg on day 3 (total 25 mg/kg over 3 days)
- Primaquine: 0.25 mg/kg/day for 14 days for radical cure (eradication of liver hypnozoites to prevent relapse)
- MANDATORY: Test G6PD before giving primaquine — primaquine causes haemolytic anaemia in G6PD-deficient patients; in severe G6PD deficiency, omit or use a supervised weekly dose regimen
- Primaquine is contraindicated in: G6PD deficiency (severe), pregnancy, infants <6 months

P. falciparum resistance note: Chloroquine is NOT effective for P. falciparum in India due to widespread resistance — use ACT only.

Chikungunya management:
- Supportive only: paracetamol for fever, NSAIDs (ibuprofen, naproxen) for joint pain AFTER dengue has been excluded (dengue and chikungunya co-circulate; NSAIDs are contraindicated in dengue)
- No antiviral therapy available
- Physiotherapy for persistent arthritis

Scrub typhus management:
- Doxycycline: first-line
- Children ≥8 years: 2–4 mg/kg/day (max 200 mg/day) in 2 divided doses for 7 days
- Children <8 years (WHO allows doxycycline for serious infections): 2.2 mg/kg/dose twice daily
- Azithromycin: 10 mg/kg/day for 3–5 days — alternative for children <8 years (avoids dental staining risk of doxycycline, though risk is low with short courses)
- Response to doxycycline is dramatic — fever typically resolves within 24–48 hours; this 'doxycycline response' is itself a diagnostic clue
- Chloramphenicol is an alternative but less preferred (more toxicity)

Prevention — vector control:
- Aedes mosquitoes (dengue, chikungunya): eliminate breeding sites (standing water in flower pots, tyres, coolers), use bed nets, window screens, insect repellents, long-sleeved clothing; Aedes bites by day
- Anopheles mosquitoes (malaria): long-lasting insecticidal nets (LLINs), indoor residual spraying (IRS) — key NVBDCP tools; Anopheles bites at dusk/night
- Dengue vaccine: Dengvaxia (approved for prior dengue-exposed individuals ≥9 years in some countries — not in India's NIS); TAK-003 vaccine in trials
- Malaria prevention in travellers/high-risk: chemoprophylaxis (doxycycline/mefloquine) for high-risk areas

Self-Assessment — Vector-Borne Fevers

Vector-borne fever management requires integrating multiple clinical and epidemiological data points simultaneously — the day of illness, the exposure history, the vector prevalent in the area, the haematological trend, and the presence or absence of warning signs and complications. The following cases are designed to test your ability to perform this integration under realistic clinical conditions. For each case, resist the temptation to reach immediately for the most dramatic diagnosis; instead, work systematically through the fever pattern, associated features, haematological hallmarks, and epidemiological context. For treatment questions, focus on the specific drug, dose, and the critical safety checks (G6PD before primaquine, no NSAIDs before excluding dengue) that prevent iatrogenic harm in these diseases.

Case 1: An 8-year-old presents on day 6 of fever. She was improving, but today has developed abdominal pain, vomited 3 times, and has become increasingly lethargic. Haematocrit: 44% (was 36% yesterday). Platelets: 35,000/µL (was 95,000/µL yesterday). Temperature: 37.5°C (was 40°C for 5 days).

Questions:
- What disease does this child most likely have, and what is the clinical significance of the defervescence at this point?
- List the warning signs present in this case.
- What is your immediate management plan?

Case 2: A 4-year-old from Jharkhand (a high-malaria district) presents with 2 episodes of high fever with shaking chills every 48 hours. He is drowsy and has a palpable spleen. Peripheral blood smear shows ring-form trophozoites and gametocytes. Blood glucose: 1.6 mmol/L (29 mg/dL).

Questions:
- What is the most likely Plasmodium species, and what is the first emergency intervention?
- What is the appropriate drug regimen for this child's malaria?
- What test must be done before prescribing primaquine, and why?

Case 3: A 7-year-old has fever for 8 days with headache and myalgia. On examination you find a painless, black, crusted lesion in the left axilla with surrounding erythema. A maculopapular rash is present on the trunk.

Questions:
- What is the diagnosis? What is the pathognomonic sign, and what causes it?
- What is the first-line treatment and dose for this child's age?
- Why is a rapid clinical response to treatment itself diagnostically informative?