## Most Common Serovar in Severe Leptospirosis **Key Point:** Serovar Icterohaemorrhagiae is the most common cause of Weil's disease (severe leptospirosis with jaundice, renal failure, and haemorrhage) globally and in India. ### Epidemiology & Clinical Significance | Serovar | Primary Host | Clinical Severity | Geographic Distribution | |---------|--------------|-------------------|-------------------------| | **Icterohaemorrhagiae** | Rats (urban) | Severe (Weil's disease) | Worldwide, including India | | Canicola | Dogs | Mild–moderate | Sporadic in India | | Grippotyphosa | Rodents (field) | Mild–moderate | Less common in India | | Hardjo | Cattle | Mild–moderate | Occupational (farmers) | **High-Yield:** Icterohaemorrhagiae is transmitted by infected rat urine in urban and semi-urban settings. Farmers and sewage workers are at highest risk. ### Pathophysiology of Weil's Disease 1. Leptospiraemia phase (days 1–7): Fever, myalgia, headache 2. Immune phase (day 8 onwards): Jaundice, renal dysfunction, pulmonary haemorrhage 3. Icterohaemorrhagiae causes direct endothelial damage and vasculitis **Clinical Pearl:** The presence of jaundice + renal failure + haemorrhage (pulmonary or GI) in a febrile patient with occupational exposure (farmer, sewage worker, abattoir worker) strongly suggests Icterohaemorrhagiae. **Warning:** Do not confuse serovar prevalence with clinical severity. While Grippotyphosa and Hardjo are common in some regions, Icterohaemorrhagiae remains the most frequent cause of severe, life-threatening disease. ### Why Icterohaemorrhagiae? - Highest virulence among serovars - Urban rat reservoir ensures sustained transmission - Causes systemic vasculitis and multi-organ failure - Mortality rate: 5–15% (untreated) [cite:Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases Ch 273]
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