The etiologic agent of whooping cough is

• A. Bordetella pertussis
• B. Brucella suis
• C. Francisella tularensis
• D. Haemophilus ducreyi

Answer: (A)

Bordetella pertussis is the etiologic agent here. This small gram-negative coccobacillus infects the human respiratory tract, attaching to the ciliated epithelium and releasing toxins such as pertussis toxin that disrupts immune signaling and impairs mucociliary clearance. The resulting damage to the airway lining and the accumulation of secretions produce the characteristic paroxysmal coughing fits, often with a noisy inspiration (whoop) after a coughing burst, especially in unvaccinated or under-vaccinated individuals. This organism is a classic cause of whooping cough and is targeted by the pertussis component of the DTaP vaccines.

The other organisms listed cause different diseases and are not responsible for whooping cough: Brucella suis leads to brucellosis from animal exposure; Francisella tularensis causes tularemia; Haemophilus ducreyi causes chancroid.