Etiology and Epidemiology
Leptospirosis is the most widespread zoonosis in the world. Pathogenic properties in humans are attributed to the species Leptospira interrogans. These motile spirochetes stain poorly with Gram stain; therefore, dark-field microscopy or silver impregnation is used to visualize them.
Animals serve as the sources of infection: rodents, pigs, cattle, and dogs. The pathogen is shed in urine for prolonged periods, establishing both natural (near water bodies) and anthropurgic foci. The transmission mechanism is fecal-oral, with the waterborne route being predominant (swimming, drinking raw water). Farmers, veterinarians, and slaughterhouse workers are at risk, though urbanization of the disease has been observed recently due to contact with urban dogs.
Pathogenesis: from penetration to vasculitis
The bacteria penetrate through microtraumas of the skin and intact mucous membranes. Tissue macrophages perform only incomplete phagocytosis, allowing leptospires to reach lymph nodes via the lymphatic system, multiply there, and enter the bloodstream.
Via the bloodstream, the bacteria spread to the liver, kidneys, and spleen (parenchymal diffusion). The primary pathogenic mechanism is the adhesion of microbes to the endothelium of the microvasculature. Leptospiral toxins destroy the vascular wall, causing generalized capillarotoxicosis (vasculitis). This leads to increased capillary permeability, erythrocyte hemolysis, organ hemorrhages, and the development of DIC syndrome.
Clinical presentation
The incubation period lasts from several days to a month (most commonly 1–2 weeks). The disease has an acute onset and a characteristic staged progression.
Initial period (up to 1 week):
- Fever of 39–40°C with chills and wide daily fluctuations.
- Myalgia — a leading symptom (pain is especially pronounced in the calf muscles, neck, and back).
- Facial puffiness and hyperemia, conjunctival vessel injection, subconjunctival hemorrhages.
Period of peak manifestations (1–2 weeks): Toxemia and organ damage increase. Tachycardia develops, blood pressure drops, and oliguria appears (dark-colored urine). Two main clinical forms develop:
- Anicteric form (up to 90% of cases) — milder course, fatal outcomes are rare.
- Icteric form — accompanied by jaundice, hepatomegaly, and worsening hemorrhagic syndrome. Associated with high mortality, which reaches 15–20% during epidemic outbreaks.
Complications and diagnostics
The most frequent and dangerous complication of leptospirosis is AKI (acute kidney injury) with azotemia, which develops as early as the first week and serves as the main cause of patient death. Other life-threatening conditions include DIC syndrome, infectious-toxic shock, acute liver failure, and pulmonary hemorrhage. Prolonged ocular lesions (uveitis, iridocyclitis) are considered specific complications.
Taking a detailed epidemiological history is critical for confirming the diagnosis. Laboratory diagnostics include dark-field microscopy of blood, urine, and CSF, as well as serological methods: indirect hemagglutination assay (IHA), and the microscopic agglutination-lysis test.
Important: any patient with suspected leptospirosis requires mandatory hospitalization in an infectious diseases hospital.
Briefly: answers to topical questions
Which antibacterial drugs are used for etiotropic therapy of leptospirosis?
Antibacterial drugs are used for the etiotropic therapy of leptospirosis, with the choice depending on the severity of the disease.
- For mild-to-moderate cases:
- Doxycycline is the drug of choice (100 mg twice daily per os for 7 days).
- Ampicillin, amoxicillin, azithromycin are alternative agents for oral administration in standard therapeutic doses.
- In severe cases:
- Benzylpenicillin is the drug of choice (6–12 million IU/day intramuscularly; up to 18–24 million IU for leptospiral meningitis).
- Penicillin G — 0.6–1 million IU/day intravenously.
- Ampicillin (500–1000 mg 4 times daily) or amoxicillin are alternative drugs for intravenous administration.
What methods are used for the serological diagnosis of leptospirosis?
Serological diagnosis of leptospirosis is performed to detect specific antibodies using several methods.
- MAT (microscopic agglutination-lysis test) is the "gold standard" of diagnostics, performed using a standard panel of live cultures.
- MA (microscopic agglutination test).
- ALTL (agglutination-lysis test for leptospires).
- IHA (indirect hemagglutination assay) — used with leptospiral diagnostic antigen.
- CFT (complement fixation test).
- ELISA (enzyme-linked immunosorbent assay) — used to determine specific IgM class antibodies (IgM-Abs).
What pathological changes are detected in a routine urinalysis in leptospirosis?
A routine urinalysis in leptospirosis reveals a complex of pathological changes indicating renal involvement in the infectious process.
The main changes include:
- Proteinuria — pathological increase in urinary protein levels.
- Leukocyturia — presence of leukocytes in the sediment.
- Cylindruria — appearance of casts.
- Microhematuria or hematuria — detection of blood (erythrocytes) in the urine, which is frequently observed during the disease.
What changes in the complete blood count are observed during the peak period of leptospirosis?
The complete blood count (hemogram) during the peak period of leptospirosis shows pronounced inflammatory changes.
The following abnormalities are detected:
- Leukocytosis — an increase in the total leukocyte count (ranging from 12–20 × 10⁹/L).
- Neutrophilia — accompanied by a characteristic left shift of the leukocyte differential.
- Marked acceleration of ESR — increased erythrocyte sedimentation rate, reaching 40–60 mm/h.
How to remember the typical clinical portrait: a farmer after working in a flooded meadow. He presents with fever, jaundice, a red face with conjunctival injection (eyes red like a rabbit's), as well as agonizing pain in the calves and lower back.
Class and exam questions
Why does hemorrhagic syndrome develop in leptospirosis?
The pathogen adheres to the endothelium and releases pathogenicity factors, causing vasculitis, generalized capillarotoxicosis, and disseminated intravascular coagulation (DIC).
Which form of leptospirosis is most common?
In the vast majority of cases (up to 90%), the disease presents in the anicteric form, which has a more favorable prognosis.
Why is leptospirosis difficult to diagnose using standard microscopy?
Bacteria of the genus Leptospira stain extremely poorly with Gram and Romanowsky-Giemsa stains; therefore, dark-field microscopy or silver staining is required for their detection.
What else to study on this topic
- Structure of leptospiral pathogenicity factors (role of the lipopolysaccharide complex and cytotoxins)
- Differential diagnosis with hemorrhagic fever with renal syndrome (HFRS)
- Pathomorphological changes in organs (renal tubular necrosis, centrilobular hepatic necrosis)
- Features of leptospirosis in children (development of Kawasaki-like syndrome)
- Principles of etiotropic therapy and use of anti-leptospiral gamma globulin
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