Transmission and Sources:
- Zoonotic Transmission: Primarily via contact with urine of infected animals (rodents, livestock, dogs).
- Human-to-Human Transmission: Rare, but recent evidence suggests household clustering, asymptomatic renal colonization, and prolonged leptospire excretion may indicate unrecognized human sources.
- Environmental Survival: Leptospires can persist in moist environments (e.g., soil, water) for weeks, facilitating indirect transmission.
- Unusual Routes: Laboratory accidents, immersion in contaminated water (e.g., car accidents), and animal bites have been documented as less common routes.
- Epidemiology:
- Seasonality: Peaks in summer/fall (temperate regions) and rainy seasons (tropics).
- Global Burden: Estimated 1 million severe cases annually, with significant underreporting likely due to nonspecific symptoms and diagnostic challenges.
- Clinical Considerations:
- Asymptomatic Carriers: Some individuals may excrete leptospires without symptoms, complicating control efforts.
- Diagnosis: Requires serology (MAT, ELISA) or PCR in early disease; culture is insensitive and slow.
- Prevention: Vaccines for livestock exist, but no human vaccine is widely available. Public health measures focus on rodent control and safe water management.
Rationale: Recent data challenge the assumption that leptospirosis is solely a zoonosis, highlighting the need for broader surveillance and infection control strategies.