Hemophiliacs, bacillus influenzae.

The influenza bacillus - Haemophilus influenzae - is often present on the mucous membrane of the upper respiratory tract of a healthy person. When the body's resistance is weakened, it can cause meningitis (especially in weakened children), bronchitis, pneumonia, purulent pleurisy, tracheitis, laryngitis, conjunctivitis, otitis and other diseases.

The causative agent of hemophilic infection was discovered by M. I. Afanasyev (1891) and described by R. Pfeiffer and S. Kitazato in 1892 during the influenza pandemic, the cause of which was mistakenly believed to be the influenza bacillus for more than 40 years.

The genus Haemophilus is part of the Pasteurellaceae family and consists of 16 species. Two species are pathogenic for humans: Haemophilus influenzae, the causative agent of inflammatory processes in the respiratory tract, and Haemophilus ducreyi, the causative agent of chancroid; this disease has not been detected in Russia since 1961.

Hemophiles are short coccoid rods measuring 0.3-0.4 x 1.0-1.5 µm. Sometimes they are located in short chains, more often - singly. They are very polymorphic, can form threads, which depends on the cultivation conditions; immobile, do not have spores. The influenza bacillus in the body and in the first generations on nutrient media can have a capsule. Bacteria are slowly stained with aniline dyes: Pfeiffer fuchsin stains within 5-15 minutes.

Bacteria of the genus Haemophilus belong to the group of hemophilic bacteria. They require rich nutrient media for cultivation, usually containing blood or its preparations. For their growth, the presence of hemin or some other porphyrins (X-factor) and/or nicotinamide adenine dinucleotide (V-factor) in the medium is required. It has been established that of the 16 known representatives of the genus Haemophilus, 2 species (H influenzae and H haemolyticus) require both the X-factor and V-factor, 4 species require only the X-factor, and 10 species require only the V-factor. The X-factor is heat-stable, and the blood of various animals or an aqueous solution of hematin chloride are used as its sources. The V-factor is heat-labile and is contained in the tissues of plants, animals, and is produced by many bacteria.

The influenza bacillus is a facultative anaerobe, the optimal temperature for its growth is 37 °C. The G + C content in DNA is 39-42 mol %. On "chocolate" agar (agar with heated blood), influenza bacillus colonies grow in 36-48 hours and reach a diameter of 1 mm. On blood agar with the addition of brain-heart extract, small, round, convex colonies with iridescent colors grow after 24 hours. There is no hemolysis. Colonies of non-capsular variants do not have iridescent colors. On liquid media with the addition of blood, diffuse growth is observed, sometimes whitish flakes and sediment are formed at the bottom.

A specific feature of influenza bacilli is the ability of their colonies to grow much faster and be larger near colonies of staphylococci or other bacteria ("satellite" growth). Pneumococci are inhibitors of influenza bacilli growth.

Saccharolytic properties are weakly expressed and inconstant. Usually ferments with the formation of acid ribose, galactose and glucose, has urease activity, has alkaline phosphatase, reduces nitrates to nitrites. According to the ability to form urease, indole and ornithine decarboxylase, H. influenzae is divided into six biotypes (I-VI).

Capsular strains of the influenza bacillus are divided into 6 serotypes by the specificity of the polysaccharide antigen: a, b, c, d, e, f. This antigen sometimes gives a cross-reaction with the antigens of capsular pneumococci. The capsular polysaccharide antigen is detected by the capsule swelling reaction, RIF, and the precipitation reaction in agar. Serovarian b is most often isolated from sick people. In addition to the capsular antigen, the influenza pathogen has a somatic antigen, which contains thermostable and thermolabile proteins.

The influenza bacillus does not produce exotoxins; its pathogenicity is associated with a heat-stable endotoxin released during the destruction of bacterial cells. Invasiveness and suppression of phagocytosis are associated with the presence of a capsule.

In the external environment, the pathogen is unstable, quickly dies under the influence of direct sunlight and ultraviolet rays and disinfectants in normal working concentrations. At a temperature of 60 °C, it dies within 5-10 minutes.

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Immunity

Children in the first three months of life are less susceptible to the influenza pathogen, as their serum contains antibodies transferred through the placenta from the mother. Subsequently, they disappear, and the child becomes susceptible to the pathogen. The infection may be asymptomatic or with damage to the respiratory tract. Meningitis most often develops in children aged 6 months to 3 years. By 3-5 years, many children develop complement-binding and bactericidal antibodies to the capsular polysaccharide antigen (polyribose phosphate).

Epidemiology of Haemophilus influenzae infection

The source of infection in diseases caused by the influenza bacillus are sick people; capsular strains in this case are transmitted from person to person by airborne droplets. Often the disease develops as a manifestation of autoinfection when the body's reactivity decreases due to some other disease, such as influenza. In healthy people, the influenza bacillus is found not only on the mucous membrane of the upper respiratory tract, but also in the oral cavity, middle ear, and sometimes on the mucous membrane of the vagina.

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Symptoms of Haemophilus influenzae infection

Associated primarily with the characteristics of the pathogen (whether it has a capsule or not), as well as with the underlying disease, against which the resistance of the macroorganism decreases. The influenza bacillus can multiply on the mucous membranes both extra- and intracellularly, sometimes penetrating into the blood. In this case, the pathogen can then penetrate the blood-brain barrier and cause meningitis. The influenza bacillus, along with meningococci and pneumococci, is one of the most common pathogens of meningitis. Mortality with such untreated meningitis can reach 90%. The clinical picture is determined by the dominant symptoms in each specific case, depending on the degree of damage to a particular organ.

Laboratory diagnostics of hemophilic infection

To diagnose diseases caused by the influenza bacillus, RIF, the bacteriological method and serological reactions are used. With a sufficient concentration of the pathogen in the material being studied (pus, mucus, cerebrospinal fluid), it can be easily and quickly detected using the capsule swelling reaction and RIF; cerebrospinal fluid can also be examined using the counter immunoelectrophoresis method. A pure culture is isolated by sowing the material on special nutrient media (chocolate agar, Levinthal medium, brain heart agar); typical colonies are identified by the capsule swelling reaction, the need for growth factors and other tests (biochemical properties, precipitation reactions in agar, etc.). Agglutination and precipitation reactions can be used for serological diagnostics.

Specific prevention and treatment of hemophilic infection

For prevention, a vaccine against Haemophilus influenzae infection from capsular polysaccharide (polyribose phosphate) is used. Currently, diseases caused by Haemophilus influenzae type b are considered candidates for eradication. For treatment, aminoglycosides, chloramphenicol, sulfonamides are most effective, however, the degree of sensitivity to antibiotics must be determined for the isolated pathogens.