What is Anthrax?
Anthrax – an acute zoonotic infection that occurs with severe intoxication, the formation of carbuncles on the skin (skin form) or in the form of sepsis.
Brief historical information
The disease has been known since antiquity under various names: “sacred fire”, “Persian fire”, “Uglevik”, etc. In Russia, it was called “anthrax” in connection with the prevailing spread in Siberia. Currently, the disease occurs in isolated cases. The identity of the infection in animals and humans and the possibility of its transmission from sick animals to humans have been proved by S.S. Andreevsky in the experience of self-infection (1788). The causative agent of the disease is described by F. Pollender, F. Browell and K. Daven (1849-1850); R. Koch distinguished pure culture (1876). An outstanding role in the study of anthrax belongs to domestic scientists – I.I. Mechnikov, G.N. Minhu, N.F. Gamalee, A.A. Vladimirov, L.S. Tsenkovsky and others.
Causes of Anthrax
The causative agent is an anaerobic, fixed, gram-positive spore-forming encapsulated bacterium B. anthracis of the Bacillus genus of the Bacillusae family. Morphologically it looks like a large stick with chopped off ends. In smears it is located singly, in pairs or chains. In the presence of oxygen it forms spores. It grows well in meat-peptone environments. The antigenic structure of the pathogen is represented by a capsular and somatic antigen, antibodies to them do not have protective properties. Pathogenicity of the pathogen is determined by the presence of a capsule and exotoxin synthesis. The anthracic sticks can secrete a strong protein exotoxin, which has both inflammatory and lethal effects. It consists of three components, or factors: edematous, protective antigen (non-toxic, exhibits immunogenic properties) and the actual lethal factor. Its combined effect on the human body is manifested by tissue edema, impaired tissue respiration processes, and inhibition of phagocytic activity. The anthrax exotoxin is extremely labile: it is completely destroyed after half an hour heating at 60 ° C.
Temperature optimum for growth of 35-37 ° С, optimum pH 7.2-7.6. Vegetative forms are unstable in the environment, quickly die when heated and boiled, under the action of conventional disinfectants. Disputes are very stable, they can persist for a long time under the most unfavorable conditions in water for several years, in soil for decades. After 5 minutes of boiling, the spores retain the ability to vegetate. Under the action of a flowing steam die only after 12-15 minutes, at 110 ° C – after 5-10 minutes. Dry heat (140 ° C) kills spores after 3 hours. Under the action of 1% formalin solution and 10% NaOH solution die after 2 hours. In the soil, the spores of the anthrax pathogen not only survive for a long time, but under certain conditions they can germinate and re-form disputes, supporting the existence of a soil focus.
The reservoir and source of infection – herbivores (large and small cattle, horses, camels, pigs, etc.). The period of contagiousness of the source is equal to the period of the disease of animals, during which they release pathogens with urine, feces, and bloody secretions. Among animals, the nutritional route of transmission of the pathogen is of particular epizootological importance: when eating feed or drinking water contaminated with anthrax spores. The transmissible route of transmission is realized through the bites of flies, gadflies that carry the pathogen from sick animals, infected corpses and environmental objects to healthy animals. Unopened corpse of a sick animal is contagious for 7 days. Received from the sick animal raw materials (wool, skin, etc.) and its products are dangerous for many years. In the soil, the pathogen can not only persist, but also under certain conditions (temperature not lower than 12-15 ° С, humidity 29-85%, neutral or slightly alkaline environment, etc.) grow into a vegetative form. Soil anthrax foci retain potential epizootic and epidemic hazards for decades. During construction, irrigation and drainage and other earthworks, as well as with storm and flood waters, spores can be brought to the surface of the soil, creating the possibility of infecting animals and people. Reliable cases of human infection from humans are unknown, but humans can be a source of animal infection. A sick person does not pose a danger to healthy individuals, which can be explained by the peculiarities of the mechanism of transmission of infection, which is realized among animals or from animal to man and impossible among people.
The transmission mechanism is diverse, most often contact. The pathogen enters the body through damaged skin, microtrauma of the mucous membranes. Infection often occurs in the process of caring for a sick animal, slaughtering, cutting carcasses, cooking meat, working with animal raw materials and making items from it (sheepskin coats, shaving brushes, etc.). Extremely rare cases of foodborne infection, as well as inhalation of an infected aerosol, are known. Transmission factors are infected livestock products, raw materials, processed products, contaminated environmental objects and animal care equipment. Infection in the pathogen through the respiratory tract in the past has been repeatedly noted in paper and wool-processing enterprises. “Disease of rags” was widespread in Russia with collectors of landfill rags contaminated with excreta and manure of animals.
The natural susceptibility of people is relatively low (about 20% of people exposed to the risk of infection fall ill), but almost universal with airborne (dusty) infection. Those who have been ill remain strong immunity, repeated cases of disease are extremely rare.
Major epidemiological signs. Anthrax is ubiquitous; most cases are recorded mainly in the developing countries of Asia, Africa and South America. Diseases are found in regions with developed animal husbandry. The seasonality of the incidence of people to a certain extent repeats the summer-autumn character of the incidence of animals. Register sporadic cases and group diseases. The main causes of group diseases are non-compliance with veterinary and sanitary requirements regarding the prevention of anthrax by private livestock owners, farm managers, trading and purchasing organizations and enterprises of various forms of ownership engaged in the procurement, processing and sale of meat and meat products.
Diseases predominate in rural areas among people of active age, more often than males. There are household and occupational incidence of anthrax. Infections in urban areas are associated with the harvesting, storage, processing of animal raw materials, with violations of the technological regime and safety regulations. Sometimes diseases are met during earthworks; known cases of laboratory infection.
Anthrax pathogen spores can be applied as a means of bioterrorism, as the events in the USA clearly demonstrated in the autumn of 2001.