Diphtheria is an acute, life-threatening, infectious disease. Children aged 3–7 years are most susceptible to it; in recent years, the incidence of adolescents and adults has increased.
Diphtheria is an acute, life-threatening, infectious disease. It proceeds in the form of acute inflammation of the upper respiratory tract, mainly the pharynx (approximately 90% of cases), the nose, the skin at the sites of damage, eyes or genitals.
The main threat, however, is not inflammation, but poisoning with a toxin, which is produced by the bacterium, the causative agent of the disease, while the cardiovascular and nervous systems are mainly affected.
The causative agent of diphtheria and infection
The causative agent of diphtheria is Corynebacterium diphteriae – gram-positive bacteria in the form of sticks with characteristic bulbous thickenings at the ends, which are placed in pairs in swabs, at an angle in the form of a Roman numeral V with respect to each other. Diphtheria bacilli secrete diphtheria toxin, the enzyme neuraminidase and other biochemically active compounds in the process of life.
The synthesis of diphtheria toxin by microbial cells is controlled by a special tox gene. Bacteria can lose it in the process of life, losing along with it their ability to produce toxin (toxigenicity). And, on the contrary, initially non-toxigenic strains can acquire pathogenic properties, fortunately, this happens extremely rarely.
The disease is transmitted by airborne droplets from patients with diphtheria or from healthy carriers of infection, much less often through household items.
Children aged 3–7 years are most susceptible to diphtheria infection, but in recent years the incidence of adolescents and adults has increased.
The source of infection is sick people or healthy carriers of toxigenic bacteria. The most contagious are diphtheria of the pharynx, nose and larynx, since they actively excrete pathogens of the disease with exhaled air. Patients with diphtheria of the eyes, skin can spread the infection by contact (hands, household items). Healthy carriers of bacteria are much less contagious, but the absence of any external signs of their condition does not allow them to control the spread of infection, because they can only be detected by chance during mass dispensary examinations. As a result, most cases of diphtheria infection are due to contact with healthy carriers of diphtheria bacillus.
The incubation period (the time from the moment of infection to the appearance of the first signs of the disease) is 2-10 days.
The toxin produced by diphtheria bacillus consists of several components. One of them – the enzyme hyaluronidase destroys the capillaries hyaluronic acid and increases their permeability, which leads to the exit of blood vessels and the impregnation of surrounding tissues with blood plasma with the deposition of fibrinogen protein. The second component – necrotoxin destroys epithelial cells with the release of the thrombokinase enzyme from them. Thrombokinase promotes the conversion of fibrinogen to fibrin and the formation of a fibrin film on the surface of tissues. Under the action of diphtheria toxin on the tonsils, which are covered with several layers of epithelial cells, a fibrin film is formed, penetrating deep into the tonsil epithelium and tightly soldered to it.
The third (main) component – the toxin itself is capable of blocking the processes of cellular respiration and the synthesis of protein molecules. The most sensitive to its action are capillaries, myocardial cells and nerve cells. As a result, myocardial dystrophy and infectious toxic myocarditis develops, capillary damage leads to an toxic toxic shock, damage to Schwann cells (auxiliary cells of nerve tissue) leads to demyelination of nerve fibers (destruction of the electrically insulating layer of myelin with impaired conduction of nerve impulses along nerve fibers). In addition, diphtheria toxin causes general intoxication of the body.
Symptoms and course
Pharyngeal diphtheria usually begins with a slight increase in temperature, slight soreness when swallowing, redness and swelling of the tonsils, the formation of a specific membranous plaque on them, an increase in the anterior upper cervical lymph nodes. The color of the films is usually white in the first 2–3 days of illness, but then acquires a gray or yellowish-gray color. After about a week, the disease either ends in recovery (a mild form, as a rule, in those vaccinated against diphtheria), or passes into a more severe toxic form due to the systemic effect of diphtheria toxin.
The toxic form of diphtheria is always very difficult. It is characterized by a very high body temperature (39.5-41.0 ° C), severe headaches, drowsiness, and apathy. The skin becomes pale, dry mouth is noted, repeated vomiting and abdominal pain is possible in children. Swelling of the tonsils becomes pronounced, can lead to a complete closure of the entrance to the pharynx, spreads to the soft and hard palate, often also to the nasopharynx.