Bordetella pertussis

Bordetella pertussis

• Gram-negative coccobacilli
• Due to filamentous haemagglutinin : have tropism for bronchial epithelium
Growth requirements
• Strict aerobe
• Enriched media containing blood, albumin & starch :
Bordet-Gengou medium
• Split pearls or mercury drops colonies

EXOTOXINS & PATHOGENESIS

1. Pertussis Toxin
• Stimulates adenylate cyclase like diphtheria & cholera
• Inhibits lymphocytes to enter lymphoid tissues - striking lymphocytosis
pertussis toxin causes a striking lymphocytosis in the blood of patients with pertussis. The toxin inhibits signal transduction by chemokine receptors, resulting in a failure of lymphocytes to enter lymphoid tissue such as the spleen and lymph nodes. Because the lymphocytes do not enter lymphoid tissue, there is an increase in their number in the blood.
2. Invasive Adenylate Cyclase
• Taken up by phagocytic cells - inhibits their phagocytic activity
3. Tracheal cytotoxin
• Damages ciliated cells of respiratory tract
• The organism is non-invasive : no bacteremia
Clinical features of whooping cough
• Source of infection : patient with whooping cough
• Mode of Transmission : droplet infection
• Incubation period : 7-10 days
STAGES
1. Catarrhal (1-2 weeks)
• Fever, sneezing, rhinorrhoea
• Highly communicable - large no. of organisms are present in nasopharyngeal secretions
2. Paroxysmal (2-4 weeks)
• Paroxysmal cough with an inspiratory whoop
• Vomiting
• Exhausted child - difficult breathing
3. Convalescent (3-4 weeks)
• Severity of symptoms fades.

Lab identification:
Specimen :
• Nasopharyngeal swab
• Culture plate placed in front of mouth when patient is coughing
Culture
• On Bordet-Gengou medium
Immunofluorescence staining
• for rapid diagnosis
(Organism not found in blood)

TREATMENT
Supportive
• Oxygen
• Suction of mucous in infants
Antibiotics : Erythomycin or ampicillin
• Reduces no. of organisms in throat but little influence on course of disease.
PREVENTION
Vaccination: Pertussis vaccine incorporated with Diphtheria & Tetanus (DPT)
• Given in first year of life.