Description. Pathogenecity, mode of infection, incubation period and toxigencity of :-Haemophilus

1. Description:

Haemophilus is a genus of Gram-negative, pleomorphic, non-motile coccobacilli. They are facultative anaerobes and require specific growth factors such as X factor (hemin) and V factor (NAD+) for growth, particularly on chocolate agar.

• The most clinically significant species is Haemophilus influenzae.
• Other notable species include Haemophilus ducreyi (causes chancroid), Haemophilus parainfluenzae, and Haemophilus aegyptius (associated with conjunctivitis).

2. Pathogenicity:

Haemophilus influenzae, especially type b (Hib), is the most pathogenic:

• Hib can cause:

• Meningitis (especially in children under 5)
• Epiglottitis
• Pneumonia
• Septicemia
• Otitis media
• Sinusitis

• Non-typeable strains (NTHi, which lack a capsule) mainly cause:

• Otitis media
• Bronchitis
• Exacerbations of chronic obstructive pulmonary disease (COPD)

Haemophilus ducreyi causes chancroid, a sexually transmitted infection presenting with painful genital ulcers and inguinal lymphadenopathy.

3. Mode of Infection:

• Haemophilus influenzae:

• Spread via respiratory droplets.
• Enters through the nasopharynx, may colonize and invade mucosal surfaces.
• Invasive disease occurs when the bacteria breach the mucosal barrier and enter the bloodstream or CNS.

• Haemophilus ducreyi:

• Sexual transmission, infects via microabrasions in genital mucosa.

4. Incubation Period:

• Haemophilus influenzae (type b):

• 2 to 4 days for upper respiratory tract symptoms.
• Invasive diseases (like meningitis or epiglottitis) may present shortly after initial colonization.

• Haemophilus ducreyi:

• Incubation period is usually 4 to 7 days, but can range from 1 to 14 days.

5. Toxigenicity:

• Haemophilus species do not produce classical exotoxins.
• Pathogenicity is mainly due to:
• Capsule (especially in Hib): major virulence factor, anti-phagocytic.
• Endotoxin (LPS/LOS): contributes to inflammation and systemic symptoms.
• IgA protease: helps bacteria evade mucosal immunity.
• Adhesins and pili: allow attachment to respiratory epithelium.