Causes and pathogenesis of hemophilic infection
Last reviewed: 23.04.2024
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Causes of Haemophilus Infection
Hemophilus infection is caused by the bacterium Haemophilus influenzae (H. Influenzae, syn. - Pfeiffer's wand). Hemophilic rod of the genus Haemophilus (family Pasteurellaceae) - small coccobacillus, can have a polysaccharide capsule. In the environment it is unstable. Has K- and O-antigens. Six serovars are isolated from the capsule antigen (a, b. C, d, e, f). Of the representatives of Hemophilus for man, only H. Influenzae type b (Hib) is pathogenic . The main factors of pathogenicity are the capsule and the saw. The capsule suppresses the phagocytic activity of leukocytes, the saws ensure the adhesion of the pathogen to the cells of the epithelium. Additional pathogenicity factors are IgA-proteases that cleave secretory immunoglobulins. The causative agent also contains a lipopolysaccharide and glycoprotein complex. There is evidence of the significant role of LPS in the pathogenesis of IHT in patients with Hib infection. H. Influenzae is poorly tolerant in the environment. It kills for 30 minutes at a temperature of 55 ° C, under the influence of sunlight and when it dries. Disinfecting solutions in commonly used concentrations kill H. Influenzae in a few minutes.
[Pathogenesis of Hemophilus Infection
The entrance gate of the infection is the mucosa of the upper respiratory tract, where the pathogen can persistently asymptomatically persist. With this localization of the pathogen, ARI caused by Hib, epiglottitis, otitis, sinusitis are associated. The mechanism of development of hemophilic pneumonia is unknown. In case of violation or inadequacy of the mechanisms of protection, the causative agent overcomes the mucosal barrier and enters the blood. Bacteremia leads to the development of septicemia (ITH can be complicated). Arthritis, osteomyelitis and meningitis as a result of penetration of the pathogen through the BBB. In this case, the protective resources of the body are limited by phagocytosis, which explains the high lethality (over 50%) in the absence of adequate therapy. Hemophilic meningitis (Hib-meningitis) is the most common and frequent form of Hib infection. In the development of the disease, three phases are identified:
- phase of respiratory infection;
- bacteremia (frequency of allocation of blood culture more than 60%);
- phase of meningitis.
Epidemiology of Haemophilus Infections
Source of infection - patients with any clinical form of Hib infection. As well as healthy carriers. The frequency of nasopharyngeal carriage of hemophils can reach 90%, but capsular strains of Hib, with which almost all cases are associated, are found only in 3-5% of the examined. The main path of transmission of the pathogen is airborne; a contact path is also possible. Human susceptibility is poorly understood. It is known that the probability of infection in children from 3 months to 5 years is 6,000 times higher than in other age groups. Apparently, the high susceptibility of children under 5 years (more than 90% of patients) is due not only to lack of immunity, but also to anatomical and physiological characteristics.