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Causes and pathogenesis of hemophilus influenzae infection
Last reviewed: 04.07.2025
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Causes of Haemophilus influenzae infection
Haemophilus influenzae infection is caused by the bacterium Haemophilus influenzae (H. influenzae, syn. - Pfeiffer's bacillus). Haemophilus influenzae of the genus Haemophilus (family Pasteurellaceae) is a small coccobacillus, may have a polysaccharide capsule. It is unstable in the environment. It has K and O antigens. According to the capsular antigen, six serovars are distinguished (a, b. c, d, e, f). Of the representatives of Hemophilus, onlyH. influenzae type b (Hib) is pathogenic for humans. The main pathogenicity factors are the capsule and pili. The capsule suppresses the phagocytic activity of leukocytes, the pili ensure adhesion of the pathogen to the epithelial cells. Additional pathogenicity factors are IgA proteases that break down secretory immunoglobulins. The pathogen also contains a lipopolysaccharide and glycoprotein complex. There is evidence of a significant role of LPS in the pathogenesis of ISS in patients with Hib infection. H. influenzae is unstable in the environment. It dies within 30 minutes at a temperature of 55 °C, under the influence of sunlight and when dried. Disinfectant solutions in concentrations commonly used in practice kill H. influenzae within a few minutes.
[ Pathogenesis of hemophilic infection
The entry point for infection is the mucous membrane of the upper respiratory tract, where the pathogen can persist for a long time without symptoms. Acute respiratory infections caused by Hib, epiglottitis, otitis, and sinusitis are associated with this localization of the pathogen. The mechanism of development of hemophilic pneumonia is unknown. If the defense mechanisms are impaired or inadequate, the pathogen overcomes the mucous membrane barrier and enters the blood. Bacteremia leads to the development of septicemia (may be complicated by IBS). arthritis, osteomyelitis, and meningitis as a result of penetration of the pathogen through the BBB. In this case, the body's defenses are limited to phagocytosis, which explains the high mortality rate (over 50%) in the absence of adequate therapy. Hemophilic meningitis (Hib meningitis) is the most typical and common form of Hib infection. Three phases are identified in the development of the disease:
- respiratory infection phase;
- bacteremia (blood culture frequency over 60%);
- meningitis phase.
Epidemiology of Haemophilus influenzae infection
The source of infection is patients with any clinical form of Hib infection, as well as healthy carriers. The frequency of nasopharyngeal carriage of hemophiliacs can reach 90%, but capsular strains of Hib, which are associated with almost all cases of the disease, are found in only 3-5% of those examined. The main route of transmission of the pathogen is airborne; contact is also possible. Human susceptibility has been poorly studied. It is known that the probability of infection in children from 3 months to 5 years is 6000 times higher than in other age groups. Apparently, the high susceptibility of children under 5 years of age (more than 90% of patients) is due not only to the lack of immunity, but also to anatomical and physiological characteristics.