What causes leptospirosis?

Causes of leptospirosis

The genus Leptospira of the family Leptospiraceae is represented by two species: parasitic - L. Interrogans and saprophytic - L. Biflexa. Both species are divided into numerous serotypes. The latter are the main taxonomic unit that forms serological groups. The classification of leptospira is based on the constancy of their antigenic structure. To date, we know 25 gray-ghipp, which unite about 200 pathogenic serotypes of leptospira. The causative agent of leptospirosis of humans and animals is referred to as L. Interrogans. Serogroups of L. Interrogans icterohaemorragiae, affecting gray rats, L. Interrogans pomona, affecting pigs, L. Interrogans canicola - dogs, as well as L. Interrogans grippotyphosa, L. Interrogans hebdomadis, are of greatest importance in the structure of morbidity .

Leptospira are thin, mobile microorganisms of spiral shape with a length of several to 40 nm and more and a diameter of 0.3 to 0.5 nm. Both ends of the leptospira are usually bent in the form of hooks, but there are also forms without a hook. Leptospira have three basic structural elements: the outer shell, the axial filament and the cytoplasmic cylinder, which is screw-like twisted around the longitudinal axis. They reproduce by means of transverse division.

Leptospira are gram-negative. These are strict aerobes; they are grown on nutrient media containing serum. The optimum growth is 27-30 ° C, but even in such conditions they grow extremely slowly. Pathogenicity factors leptospira - exotoxin-like substances, endotoxin, enzymes (fibrinolysin, coagulase, lipase, etc.), as well as invasive and adhesive ability. Leptospira sensitive to high temperatures: boiling them kills instantly, heating to 56-60 ° C - for 20 minutes. To the effect of low temperatures leptospires are more stable. So, at -30-70 ° C and in frozen organs they retain viability and virulence for many months. Bile, gastric juice and man's acid urine are destructive to leptospira, and in the slightly alkaline urine of herbivores they remain viable for several days. In the water of open reservoirs with weakly alkaline or neutral reaction, leptospires persist for 1 month, and in the moist and wetland they do not lose pathogenicity until 9 months. Leptospira are susceptible to penicillin, chloramphenicol, tetracycline, and extremely sensitive to the action of conventional disinfectants, boiling, pickling and pickling on food. Leptospira survive up to 1-2 days, and under the influence of ultraviolet and during drying, die within 2 hours. At the same time, low temperatures do not have a harmful effect on leptospira. This explains their ability to hibernate in open reservoirs and wet soil, completely preserving virulence.

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Pathogenesis of leptospirosis

The causative agent penetrates into the human body due to its mobility. The entrance gates are microdamages of the skin and mucous membranes of the mouth, esophagus, conjunctiva of the eyes, etc. There are cases of laboratory infection through the damaged skin. When intracutaneous penetration in an experiment on laboratory animals, leptospira penetrate into the blood after 5-60 minutes, apparently bypassing the lymph nodes that do not fulfill the barrier function in leptospirosis. At the site of the pathogen introduction, there is no primary affect. Further spread of leptospira occurs by hematogenous way, while lymphatic vessels and regional lymph nodes also remain intact. With the blood flow, the leptospirae enter various organs and tissues: the liver, the spleen, the kidneys, the lungs, the central nervous system, where they multiply and accumulate. The first phase of infection lasts from 3 to 8 days, which corresponds to the incubation period.

The second phase of the pathogenesis of leptospirosis is secondary bacteremia, when the amount of leptospira in the blood reaches a maximum and they continue to multiply in the liver and spleen, adrenals, causing the clinical onset of the disease. With a current of blood, the leptospira again spread throughout the body, even overcoming the BBB. During this period, along with the multiplication of leptospira, their destruction begins as a result of the appearance of antibodies agglutinating to the fourth day of the disease and lysing leptospira. Accumulation in the body of metabolic products and decay of leptospira is accompanied by fever and intoxication. Which increases the sensitization of the body and causes hyperergic reactions. This phase lasts for 1 week. However, it can be shortened to several days. The maximum concentration of leptospira by the end of the leptospiraemia phase is observed in the liver. Leptospira produce hemolysin, which, by affecting the erythrocyte membrane, causes their hemolysis and the release of free bilirubin. In addition, the liver develops destructive changes with the formation of inflammation and swelling of the tissue. In severe disease, the main factor in the pathological process in the liver is the damage to the membranes of the blood capillaries, which explains the presence of hemorrhages and serous edema. The pathogenesis of jaundice with leptospirosis is of a twofold nature: on the one hand. Disintegration of erythrocytes due to toxic effects on the hemolysin membranes and hemolytic antigen, as well as as a result of erythrophagia by the cells of the reticuloendothelial system in the spleen, liver and other organs, on the other - as a result of developing parenchymal inflammation with violation of the bile-forming and excretory liver function.

The third phase of the pathogenesis of leptospirosis is toxic. Leptospira die due to the bactericidal action of blood and the accumulation of antibodies, disappear from the blood and accumulate in the convoluted tubules of the kidneys. The toxin accumulated due to the death of leptospira has a toxic effect on various organs and systems. In some patients, leptospires reproduce in convoluted tubules and are excreted from the body with urine. In this case, the defeat of the kidneys is at the forefront. The most characteristic lesion of the kidneys with leptospirosis is a degenerative process in the epithelium of the tubular apparatus, therefore it is more correct to treat them as diffuse distal tubular nephrosis. In patients, there are signs of acute renal failure with oligoanuria and uremic coma. Severe kidney damage is one of the most common causes of death in leptospirosis.

In the toxemia phase, damage to organs and tissues is due to the action of not only the toxin and the products of the vital activity of the leptospira, but also the autoantibodies formed as a result of the disintegration of the affected tissues and cells of the macroorganism. This period coincides with the second week of the disease, but may be somewhat delayed. The toxin has a damaging effect on the endothelium of the capillaries, which increases their permeability with the formation of thrombi and the development of LVS syndrome.

CNS is affected by the overcoming of the BBB by leptospira. Part of the patients develop serous or purulent meningitis, less often meningoencephalitis.

In some cases, there is a specific leptospirosis myocarditis.

The pathognomonic symptom of leptospirosis is the development of myositis with lesion of skeletal, especially calf muscles. Often, the lungs (leptospiroznaya pneumonia), eyes (irites, iridocyclitis), less often other organs are affected.

Epidemiology of leptospirosis

Leptospirosis is one of the most widespread natural focal infectious diseases. The source of the infectious agent is wild, agricultural and domestic animals. The role of certain animal species as a source of leptospiral infection is far from the same due to their varying sensitivity to these microorganisms and the nature of the response to infection. Animals that have a chronic and, in some cases, asymptomatic process, accompanied by prolonged release of leptospirae with urine, have the greatest epidemiological and epizootological significance. It is these animals that ensure the preservation of leptospira as a biological species. The greatest importance in the natural foci of leptospirosis is assigned to representatives of the order of rodents, as well as insectivores (hedgehogs, shrews). The carrier of leptospira was proved in almost 60 species of rodents. Of which 53 are classified as a family of mouse-like and hamster-like.

The biological plasticity of the leptosphere makes it possible to adapt them to agricultural and domestic animals (cattle, pigs, horses, dogs), as well as to the synanthropic rodents (gray rats, mice), which form anthropurgic foci of infection, which are the main danger to humans.

From the epidemiological point of view, the incidence of large and small cattle, as well as pigs, is important. Animals of any age are sick, but in adults leptospirosis proceeds more often in a latent form, and in young animals - with more severe symptoms.

A person does not matter as a source of infection.

The main factor of transmission of the causative agent of leptospirosis is water contaminated with secretions (urine) of infected animals. Immediate causes of infection of people is the use of raw water for drinking, washing from open reservoirs, bathing in small weakly flowing ponds or fording them.

Some of the importance in the transmission of infection is also in foods contaminated by rodent secretions. Transmission of the infection occurs most often through a contact route, but a food path is also possible. Transmission factors are also wet soil, pasture grass, contaminated with excrements of sick animals. Infection can occur during slaughtering of cattle, cutting carcasses, as well as when eating milk and thermally unprocessed meat. Often, people who have professional contact with sick animals are ill with leptospirosis: veterinarians, deratants and agricultural workers.

To penetrate the leptospira, the slightest violations of the integrity of the skin are enough.

Epidemic outbreaks of leptospirosis are confined, as a rule, to the summer-autumn period. The peak incidence falls on August. There are three main types of outbreaks: water, agriculture and livestock. Leptospirosis is also seen in the form of sporadic cases, which can be registered throughout the year.

Leptospira are hydrophilic, therefore, leptospirosis is characterized by high prevalence in areas where there are many marshy and strongly moistened lowlands.

The natural susceptibility of people to leptospiroznoy infection is significant. Post-infectious immunity is strong, but type-specific; therefore, repeated diseases caused by other serovars of the pathogen are possible.

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