What causes botulism?

Causes of botulism

The cause of botulism is Clostridium botulinum, gram-positive anaerobic (in young cultures) movable rod. Depending on the antigenic properties of the produced toxin, eight serovars A, B, C _1, C ₂, D, E, F and G are isolated . In Ukraine, the disease is caused by serovars A, B and E. In the course of life, the causative agent of botulism produces a specific neurotoxin. Optimal conditions for toxin formation by vegetative forms are an extremely low residual oxygen pressure (0.4-1.33 kPa) and a temperature regime within 28-35 ° C, with the exception of an E type causative agent for which strict anaerobic conditions are not required and whose reproduction is possible at the temperature of the household refrigerator (3 ° C). This toxin is the most powerful of all known toxins of any origin. The strains of the pathogen obtained in the laboratory produce a toxin, which in a purified crystalline form in 1 g contains up to 1 million lethal doses for a human. The unique toxicity and relative simplicity of production make it possible to consider the possibility of its use as a biological weapon and a means of mass destruction. Botulinum toxin is used as a medicine for the treatment of muscle contractures and in cosmetology. Botulinum toxin, produced by different serovars of the pathogen, has a single mechanism of action, differs in antigenic and physical properties, molecular weight. Warming at 80 ° C for 30 minutes causes the death of vegetative forms of the pathogen. Disputes, unlike the vegetative form, are extremely resistant to various physical and chemical factors: in particular, they can withstand boiling for 4-5 hours, the effect of high concentrations of various disinfectants. They are resistant to freezing and drying, to ultraviolet radiation. Botulinum toxin under normal environmental conditions persists up to 1 year, in canned products - for years. It is stable in acidic medium, withstands high concentrations (up to 18%) of table salt, it does not break down in products containing various spices. The toxin comparatively quickly inactivated under the influence of alkalis, during boiling completely loses its toxic properties within 10 minutes. In the GIT, toxin reduces its toxicity, with the exception of toxin E, which, when activated by trypsin, increases it by 10,000 times. Ethanol and liquids containing it, reduce the toxicity of botulinum toxin; its presence in food does not cause a change in their appearance and organoleptic properties. The "bombardment" of canned food, the smell and flavor of rancid butter are usually associated with the presence of ancillary anaerobic flora, in particular Cl. Perfringens.

[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]

Pathogenesis of botulism

In the pathogenesis of botulism, the leading role is played by toxin. When alimentary infection occurs, it enters the body together with food, which also contains the vegetative forms of the pathogen. The effect of toxin on the human body is highly specific and is not related to its antigenic structure and molecular mass. The H chain of the toxin binds to the synaptic membrane of the neuromuscular cholinergic synapses innervating the striated muscles, i.e. A-motoneurons of the anterior horns of the spinal cord and the motor nuclei of the cranial nerves, as well as smooth muscles that are innervated by the vagus nerve. The toxin, possessing protease activity, cleaves specific synaptic proteins: SNAP-25 (cleaved with toxins of serovars A and E) and synaptobrevin (cleaved by toxin of serovar B), which disrupts the fusion of synaptic vesicles and synaptic membrane, i.e. Blocks the passage of the nerve impulse during normal production of acetylcholine and cholinesterase. The blockade of impulse transmission leads to myasthenia gravis and paralytic syndrome in the absence of anatomical damages, so it is more correct to treat this syndrome as pseudo-paralytic, since inactivation of the toxin can completely restore the functions of neuromuscular synapses. It affects primarily muscles with high functional activity: oculomotor, pharynx and larynx, respiratory. The action of the toxin is potentiated by aminoglycosides, antipolarizing muscle relaxants. Ionizing radiation and repeated entry into the body of new doses of toxin. Blockade of the musculature innervated by the vagus nerve, causes paresis of the intestine, reduces the production of saliva, gastric juice. Additional factors of pathogenesis are ventilation hypoxia, aspiration of the secretion of the oropharynx, secondary bacterial infection. The clinical picture of botulism is completely formed by a toxin, but a causative agent plays a role, the vegetative forms of which in the organism can produce toxin (wound botulism, newborns' botulism, cases of illness with prolonged incubation, sudden deterioration in late illness). This is indicated by the presence of antimicrobial antibodies in some patients.

Epidemiology of botulism

Spore forms of the pathogen can be found in dust, water and mud. Almost all food products contaminated by soil or intestinal contents of animals, birds, fish, can contain spore forms of botulinum pathogens. In natural conditions, the formation of vegetative forms and botulinum toxin most intensively occurs after the death of the animal, when the temperature of the body decreases to the optimum for the pathogen. When anaerobic conditions are created as a result of oxygen consumption by aerobic bacteria, algae in the soil, bottom sediments of shallow water bodies, propagation of the vegetative forms of the pathogen and toxin formation are also possible.

The overwhelming number of cases of botulism is associated with the use of canned food (mushrooms, beans, vegetables), fish and home-cooked meat. If solid-phase product is contaminated (sausage, smoked meat, fish), then it is possible: "nodding" the formation of toxin, so not all people who use this product are ill. Significantly less frequent cases of disease as a result of infection only by spores of CI pathogens . Botulinum. To them carry so-called wound botulism and botulism of newborns.

Wound botulism can arise due to contamination of wounds, in which anaerobic conditions are created. In this case, vegetative forms germinate from the spores that wound up in the wound, which produce botulinum toxins. Botulism of babies is observed mainly in children of the first 6 months of life. Most of the patients were on partial or full artificial feeding. Sometimes spores were isolated from honey used for the preparation of nutritional mixtures, or found in the environment surrounding the child: soil, household dust of the premises and even on the skin of nursing mothers. Susceptibility to botulism is universal. Immunity in botulism type-specific antibacterial, is poorly expressed, therefore, a possible recurrence is possible.

Botulism is common in all countries where domestic canning is practiced.

[11], [12], [13], [14], [15], [16], [17], [18], [19]