Leptospirosis

Leptospirosis is a zoonotic disease caused by pathogenic, spiral-shaped bacteria called spirochaetes, belonging to the genus Leptospira. Kerala experiences a particularly high disease and mortality burden, especially during the monsoon and post-monsoon periods.

Reservoirs

Several wild and domesticated mammals can act as reservoirs of Leptospira. Important reservoirs include rodents, cattle, buffaloes, pigs, dogs, horses, sheep and goats.

Pathogenic leptospires can persist in the renal tubules and, in some animals, in the reproductive tract. Many carrier animals remain asymptomatic or develop only mild illness, while continuing to shed the bacteria through their urine for prolonged periods. Rodents are particularly important reservoirs because their urine can contaminate soil and water.

Transmission

Humans generally acquire leptospirosis through direct contact with infected animal urine or indirectly through water, soil or food contaminated with the bacteria. The organism can enter the human body through cuts, abrasions, mucous membranes or macerated skin.

Human-to-human transmission is rare, making exposure to infected animals and contaminated environments the principal routes of infection.

Symptoms and Severity

Leptospirosis can range from a mild flu-like illness to severe and potentially fatal disease. Common symptoms include fever, headache and muscle pain, generally developing around 5–14 days after exposure.

Severe infection can cause Weil’s syndrome, meningitis and pulmonary haemorrhage. Jaundice is generally associated with more severe disease.

Diagnosis

Leptospirosis is often underdiagnosed because its early symptoms can resemble several other febrile illnesses. Limited access to appropriate diagnostic tests can further contribute to missed or delayed diagnosis.

Treatment

Leptospirosis is treated with antibiotics, with the choice depending on the severity of the infection. Commonly used antibiotics include doxycycline, penicillin G and ceftriaxone.

Prevention and Control

Prevention primarily involves reducing exposure to contaminated environments and controlling animal reservoirs. Important measures include maintaining proper sanitation, avoiding contact with potentially contaminated water and soil, controlling rodents and using protective clothing during high-risk occupational or environmental exposure.

Serovar-specific vaccines are available for animals such as dogs, pigs and cattle. However, vaccination may not completely prevent renal carriage, meaning vaccinated animals may still potentially harbour the organism in their kidneys.

Geographical Distribution

Leptospirosis occurs worldwide but has a particularly high prevalence in South-East Asia. Countries such as India, Indonesia, Thailand and Sri Lanka report significant numbers of cases, with transmission generally increasing during the rainy season.

Why Kerala is Vulnerable

Kerala faces a significant leptospirosis burden because the disease is strongly associated with rainfall, flooding, contaminated water and soil, and exposure to animal urine. The risk becomes particularly important during the monsoon and post-monsoon periods, when environmental conditions favour transmission.