What causes listeriosis?

The cause of listeriosis

The cause of human listeria is a species of Listeria monocytogenes of the genus Listeria. which in accordance with the IX edition of the determinant Berdzhi refers to the 19th group of microorganisms - Gram-positive sporeforming sticks of regular shape. Listeria - facultative anaerobes. They are acid-resistant, unpretentious, spores and capsules do not form, grow well on ordinary nutrient media.

The antigenic structure of listeria is complex, there are 16 serological variants, depending on the combination of somatic (15) and flagellate (4) antigens. Listeria ferment glucose. They are catalase positive, oxidase-negative. Form cytochromes, mobile at 20-25 ° C; can be converted into L-forms and parasitize intracellularly, which causes insufficient effectiveness of antibiotic therapy in a number of cases, explains the tendency of listeriosis to protracted and chronic course, the possibility of latent form and bacterial transport.

Pathogenicity factors are listeriolysin O, which has hemolytic activity and determines virulence of the microbe; phosphatidylinositol; internalin A; internalin B; protein ActA and others.

Listeria are highly stable in the environment, grow in a wide range of temperatures (from 1 to 45 ° C) and pH (from 4 to 10), are capable of reproduction in soil, water, plants, corpses. In various foods (milk, butter, cheese, etc.) multiply at the temperature of a household refrigerator. At 70 ° C perish in 20-30 minutes, at 100 ° C - after 3-5 minutes; inactivated by a solution of formalin (0.5-1%), chloramine (3-5%) and other conventional disinfectants. Listeria are sensitive to penicillins, tetracyclines, aminoglycosides, and fluoroquinolones of the third generation.

Pathogenesis of listeriosis

Listeria penetrate the human body through the mucous membranes of the digestive tract, respiratory organs, eyes, genital tract, damaged skin, through the placenta of the pregnant woman to the fetus. In the site of the entrance gate, the inflammatory process develops, and regional lymph nodes are often involved. Resident macrophages or monocytes absorb bacteria in the process of nonspecific phagocytosis. Part of the listeria is killed, the remaining multiply intracellularly. With an adequate immune response of the body, further promotion of listeria does not occur. Otherwise, germs can spread from the entrance gates to the hematogenous and lymphogenous pathways, penetrate into the reticular-endothelial system (liver, spleen, lymph nodes), into the central nervous system, kidneys, etc., where their further multiplication takes place with the formation of granules consisting of reticular, monocytic cells, cellular detritus, altered polymorphonuclear leukocytes; In the center of the granule, there are accumulations of listeria (gram-positive argyrophilic short sticks, arranged in the form of chains or in pairs). The progression of the process causes necrotic changes in the center of the granule. Later, necrotic foci are organized, resorption of necrotic cell elements with possible scarring. Specific granulomas are most often found in the liver.

Listeria are able to overcome the BBB, to affect the membranes, the substance of the brain.

With congenital listeriosis, the granulomatous process has a generalized character, and it is treated as granulomatous sepsis. When external examination of a newborn with listeriosis, multiple white and gray granulomas 1-2 mm in diameter are detected, in some cases a rash on the skin, papular with a hemorrhagic whisk or a roseolous one. At the autopsy of the dead from listeriosis, all the organs on the surface or on a cut are sprinkled with fennel: white-gray, gray-yellow granulomas are found under the pleura, in the lungs, under the capsule of the liver and in its tissue, in the kidneys, under the soft cerebral membrane, brain, spleen, lymph nodes, intestines, stomach, adrenal gland, thymus. Microscopically, the skin is observed productive vasculitis, foci of necrosis in the dermis with the formation of granulomas, hyperemia. In the liver, multiple submillary foci of necrosis of hepatocytes with pronounced hyperplasia and proliferation of stellate endotheliocytes are identified, in the place of which the granules described above are formed.

The main role in the destruction and elimination of listeria from the body is assigned to cellular immune responses, the leading role is played by cytotoxic suppressors, to a lesser extent - helpers. The value of the humoral response is small, as in other infections with intracellular parasitism of the pathogen.

Epidemiology of listeriosis

Listeriosis is referred to as sapronosis, the main source and reservoir of the pathogen are environmental objects, primarily soil. Listeria is also distinguished from plants, silage, dust, ponds and sewage. The source of listeria is, in addition, various animals (rabbits, pigs, cows, dogs, cats, chickens, mice, rats, etc.).

The main way of human infection with listeriosis is food, with the use of various food products (meat, dairy, root crops) that have not undergone thermal treatment, especially if they have been stored in the refrigerator for a long time. The increased danger is represented by soft cheeses, sausages in vacuum packing, as well as fast food products: hot dogs , corn dogs, hamburgers, etc.

It is also possible to contact (from infected animals and rodents), aerogenic (in the premises when processing hides, wool, and also in hospitals), transmissible (with insect bites, in particular mites), sexual route of infection.

Of particular importance is the ability of the listeria to transmit vertically from the pregnant woman to the fetus during pregnancy (transplacental) or during labor (intranatally). Listeria can be the cause of nosocomial infection, in particular in maternity hospitals. The source of the causative agent of the infection is the mothers with unrecognized listeriosis or their newborns. In the human population, the asymptomatic carriage of listeria is 2-20%, from the stool of healthy people, listeria is isolated in 5-6% of cases.

Despite the fact that many food products are contaminated with Listeria and during the life of a person, infection occurs repeatedly, listeriosis becomes relatively rare: it depends on both the virulence of listeria and the state of the human immune system. The most susceptible are people with weakened immunity, especially pregnant and newborns, as well as HIV-infected, cancer patients, patients with diabetes mellitus, chronic alcoholism, etc. In connection with the possibility of infection from animals, the risk group also includes employees of livestock farms, meat processing plants, poultry farms, etc.

The current and future increase in the incidence of listeriosis is due to the high adaptive properties of listeria, their ability to reproduce in the abiotic environment, including food, the increase in the human population of people with different immunodeficiencies, the prevalence of the food pathway of infection.

After the transferred listeriosis, a prolonged immunity is formed. Repeated cases of listeriosis are not described.

The incidence is predominantly sporadic, less often group-based, and lethality reaches 15-17%.

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