What causes tetanus?

Causes of tetanus

The cause of tetanus is Clostridium tetani (genus Clostridium, the family Vasilisaeae) - a large Gram-positive rod, polytrich, has more than 20 flagella, an obligate anaerobic. When oxygen is available, it forms spores. In the process of vital activity it produces three toxic substances, has flagellum (H-Ar) and somatic (O-Ag) antigens. On the flagellate antigen, 10 serovars of the pathogen are isolated. Pathogenicity of the pathogen and all clinical manifestations of the disease are associated with tetanospazmine - a polypeptide with a mass of 150 kDa, the strongest poison, second only to botulinum toxin in toxicity.

Spores of tetanus bacillus have an extremely high resistance to the action of physical and chemical factors. In dry form, they die at a temperature of 155 ° C after 20 minutes, in 1% solution of the sulemy remain viable for 8-10 hours. The vegetative form of the pathogen in the environment is unstable.

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Pathogenesis of tetanus

Getting into the body through damage to the outer cover, the spores of the pathogen remain at the entrance gate. In the presence of anaerobic conditions (necrotic tissues, blood clots, ischemia, foreign bodies, flora consuming oxygen) and lack of adequate level of immune defense, spores grow into vegetative forms. After this, intensive production of tetanus exotoxin begins. The toxin is hematogenous, lymphogenous and perineural pathways spreading throughout the body and firmly fixed in the nerve tissue. It selectively blocks the inhibitory effect of intercalary neurons on motoneurons primarily in the motor cells of the anterior horns of the spinal cord. Pulses spontaneously arising in motoneurons are unimpeded to the striated muscles, causing their tonic tension.

It should be noted that, first of all, there is a reduction in striated muscles, which, on the one hand, are closer to the site of injury, and on the other hand, they act as relative (per unit area) "strongest" in the human body (masticatory and facial muscles) . In addition, the blockade of the neurons of the reticular formation of the brain stem contributes to the inhibition of the parasympathetic nervous system, which leads to the activation of the sympathetic nervous system, and this, in turn, causes an increase in body temperature, arterial hypertension and marked sweating, down to the development of dehydration.

The constant muscular tension is combined with a violation of microcirculation. There is a vicious cycle: metabolic acidosis and microcirculation disorders lead to the development of convulsions, and convulsive syndrome in turn aggravates metabolic acidosis and microcirculation disorders. If the patient does not die at the "peak" of a convulsive attack from a stopping of breathing or cardiac activity, then in the further course of the disease, the cause of death can be the direct action of the toxin on the respiratory and vasomotor centers in combination with deep metabolic disorders, as well as purulent-septic complications.

Epidemiology of tetanus

The source of the pathogen is many kinds of animals, especially ruminants, in the digestive tract of which spores and vegetative forms of the pathogen are found. The causative agent can also be detected in the human intestine. Falling with stool in the soil, spores of tetanus bacillus remain in it for years, and under favorable temperature conditions, lack of oxygen or consumption of its aerobic flora, they germinate, which leads to the accumulation of spores. An increase in the soil population of the pathogen is particularly characteristic of countries in the tropical belt. Thus, the soil serves as a natural reservoir of the pathogen.

Infection occurs when spores penetrate into tissues in wounds, especially fragmentation, domestic, industrial; agricultural traumas, together with soil particles, foreign bodies. In peacetime, the most frequent cause of infection is minor foot injuries, and in developing countries - umbilical cord injury in newborns. Perhaps the emergence of tetanus after burns, frostbite, community-acquired abortions, surgeries, childbirth, with various inflammatory processes, trophic ulcers, decaying tumors. Tetanus of wartime is associated with extensive wounds. Sometimes the entrance gate of infection can not be established ("cryptogenic tetanus").

Susceptibility to tetanus is high. In countries with a temperate climate, summer seasonality is noted (agricultural traumatism).

Postinfectious immunity is not produced.

The disease is recorded in all regions of the globe. The level of annual incidence depends largely on the coverage of the population with vaccination, as well as on the implementation of emergency prevention and reaches 10-50 cases per 100 000 population in developing countries. The bulk of cases in developing countries are newborns and infants. Annually, up to 400 000 newborns die. In developed countries, where mass vaccination was started in the 1950s, the incidence is almost two orders of magnitude lower. Patients with epidemiological danger do not represent.

A higher incidence is observed in a hot humid climate, which is associated with delayed wound healing. Increased contamination of the soil by the causative agent and widespread practice in a number of countries to treat the umbilical cord with soil or excrement of animals.

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