BORDETELLA PERTUSSIS

BORDETELLA PERTUSSIS

• Bordetella pertussis – gram‑negative, aerobic, non‑motile coccobacillus, 0.5‑1.5 µm, grows on Bordet‑Gengou or Regan‑Lowe medium with heated blood.

• Causative agent of whooping cough (pertussis), highly contagious droplet infection.

• Types of disease presentation

  • Classic (paroxysmal cough with whoop)
  • Atypical (mild, prolonged cough, often in adolescents)

• Transmission → inhalation of droplets → bacteria reach ciliated epithelium of trachea/bronchi.

• Pathogenesis (step‑wise)

  1. Adhesion → filamentous hemagglutinin (FHA) and pertactin bind to ciliary receptors.
  2. Colonization → microcolonies form on respiratory epithelium.
  3. Toxin production → pertussis toxin (PT), tracheal cytotoxin (TCT), adenylate cyclase toxin (ACT), dermonecrotic toxin.
  4. PT action → ADP‑ribosylates Gi proteins → ↑cAMP → lymphocytosis, systemic effects.
  5. TCT → destroys cilia → ciliostasis → impaired mucociliary clearance.
  6. ACT → inhibits phagocytosis, induces apoptosis of immune cells.
  7. Result → intense coughing, vomiting, possible hypoxia.

• Memory trick for pathogenesis: “FAT‑CAT” → FHA/pertactin, Adhesion, Toxins, Cilia loss, ACT, Toxin effects.

• Clinical manifestations

  • Incubation 7‑10 days (up to 21 days).
  • Catarrhal stage – mild rhinorrhea, low‑grade fever, occasional cough.
  • Paroxysmal stage – sudden bursts of cough → high‑pitched “whoop” on inspiration, post‑tussive vomiting, apnea in infants.
  • Convalescent stage – cough persists weeks‑months, may be triggered by cold air.
  • Complications – pneumonia, rib fractures, pulmonary hemorrhage, encephalopathy, seizures, secondary bacterial infection, death in infants.

• Laboratory diagnosis

  • Culture → Bordet‑Gengou or Regan‑Lowe agar, 37 °C, 5‑7 days → tiny dew‑drop colonies.
  • PCR → detection of IS481, pertussis toxin gene from nasopharyngeal swab/aspirate; rapid, high sensitivity.
  • Serology → ELISA for anti‑pertussis toxin IgG (single high titre or four‑fold rise) – useful after 3 weeks of illness.
  • Peripheral blood smear → marked lymphocytosis (especially in infants) – supportive clue.

• Management

  • Early macrolides – erythromycin 40 mg/kg/day in 4 doses for 14 days or azithromycin 10 mg/kg day 1 then 5 mg/kg daily for 4 days → reduces transmission, may shorten cough if given ≤3 weeks.
  • Trimethoprim‑sulfamethoxazole – alternative for macrolide‑resistant strains.
  • Supportive care – hydration, antipyretics, monitor infant apnea, oxygen if needed.
  • Vaccination – whole‑cell (wP) and acellular (aP) vaccines; aP contains detoxified PT, FHA, pertactin, fimbriae. Primary series at 6, 10, 14 weeks; boosters at 18 months, 5 years; Tdap in adolescents/adults.

• Prevention

  • High vaccine coverage → herd immunity.
  • Chemoprophylaxis for close contacts – single dose azithromycin or erythromycin.

• Key exam points from textbooks

  • Robbins – PT mechanism (ADP‑ribosylation of Gi) → lymphocytosis.
  • Harsh Mohan – description of catarrhal, paroxysmal, convalescent stages.
  • Ananthanarayan & Paniker – culture media, characteristic colony morphology.
  • Chatterjee – role of FHA and pertactin in adhesion.
  • NCH – vaccination schedule, management of infant apnea.