Leptospira belongs to the causative agents of zoonotic bacterial infection. They are characterized by wave-like fever, intoxication, and damage to the capillaries of the liver, kidneys, and central nervous system.
Leptospira is thin spirochetes. Their size is about 0.07-5-0.15 x 6-24 µm with curved ends. The motor system is represented by one fibril from each cell. The number of primary curls is 20–40 and 1-2 secondary, located at the end of the body. It seems the body takes shape of the G, S, C letters. Leptospira are weakly stained with aniline dyes. As a result, it is difficult to distinguish them on preparations according to the Giemsa stain. They do not form cysts. They reproduce by transverse fission. The main type of motion is rotational or reciprocal.
According to the Giemsa method, they become red. But when entering the body, they change their characteristic morphological features. Dark-field microscopy is used for their identification.
Cultural and biochemical properties
Aerobes. Lipids are the source of carbon and energy. They are catalase and oxidase-positive. It is cultivated on liquid salt nutrient media containing 5% -10% native rabbit serum or serum albumin, at a temperature of 28-30 °C. The peculiarity of liquid nutrient growth medium is the absence of turbidity. It rarely reaches a high density. Grow slowly (a week or later).
Nature of the distribution
Leptospira is widely distributed in nature. They inhabit soil and water bodies. The species L. interrogans is pathogenic to humans and animals. It causes leptospirosis.
L. interrogans is sensitive to drying, heating, low pH, and disinfectants. When heated to 56 °C, it dies within 25-30 minutes. Boiling kills the microbe instantly. It remains up to 30 days in water bodies, up to 280 days in moist and alkaline soils, and 1-2 days on food products.
Leptospirosis refers to a natural focal zoonosis, with a predominantly fecal-oral transmission mechanism. It is divided:
- natural reservoirs of leptospirosis. They are located in uninhabited and moist places (floodplains of rivers, lowlands, swamps, moist forests).
- anthropourgic focus. They are found in rural areas and cities.
The main reservoir and source of infection are domestic and field rodents. The additional ones are domestic animals (cattle, pigs, dogs). In wild animals, the infection has a chronic course without clinical manifestations, while the pathogen is excreted in the urine, polluting water bodies and soil. The susceptibility of people to leptospirosis is high, but people are not pathogens to leptospira into the environment.
Some species of L. interrogans are characterized by hemolytic and lipase activity, reproduce plasmocoagulase, fibrinolysin, and cytotoxins.
The site of entry is the mucous membranes of the digestive tract, damaged skin.
Having penetrated the body, the microbe spreads to the organs of the reticuloendothelial system (liver, kidneys) with blood. There it multiplies and re-enters the bloodstream. As a result, it coincides with the disease onset. By the end of 1 week of the disease, leptospira disappears from the blood, accumulates in the kidneys and excreted with the urine. Damage to the renal tubules occurs – glomerulonephritis, up to necrosis of the tubule epithelium. Mortality ranges from 3 to 25-40%. Death can be caused by hemorrhage in vital organs, acute liver or kidney failure.