Leptospirosis.

Leptospirosis is a bacterial infection caused by Leptospira spirochetes transmitted to humans through contact with water, soil, or food contaminated by infected animal urine. Most cases are mild flu-like illnesses, but 5-10% develop severe Weil's disease with jaundice, renal failure, and bleeding, and a smaller fraction develop fatal pulmonary hemorrhage.

Leptospirosis is spread by contact with water, soil, or animals contaminated with infected animal urine. Spirochetes enter through cuts, mucous membranes, or conjunctivae. Common exposures include flood water, paddy fields, rivers, sewers, and direct contact with rodents, cattle, pigs, or dogs. Human-to-human transmission is rare.

Symptoms begin 5-14 days after exposure and include sudden high fever, severe headache, intense calf and back pain, and bilateral red eyes (conjunctival suffusion) without discharge. Severe disease adds jaundice, reduced urine output, mucosal bleeding, and breathlessness from pulmonary involvement.

About 90% of cases are mild and self-limited. The remaining 5-10% develop severe disease with case-fatality rates of 5-40% in Weil's disease and 50-75% in pulmonary hemorrhage syndrome despite intensive care. Early antibiotic treatment dramatically reduces severity and mortality.

Mild disease is treated with oral doxycycline 100 mg twice daily for 7 days, or amoxicillin or azithromycin in children and pregnancy. Severe disease is treated with intravenous penicillin G or ceftriaxone for 7 days plus aggressive supportive care, including dialysis for kidney injury and ventilation for pulmonary hemorrhage.

Weil's disease is severe icteric leptospirosis: jaundice, acute kidney injury, and hemorrhage. It accounts for 5-10% of cases and carries 5-40% mortality. Hyperbilirubinemia is conjugated and renal failure is typically non-oliguric with hypokalemia. Early intravenous antibiotics and supportive care are essential.

Mild leptospirosis resolves within 5-10 days of starting antibiotics, although fatigue may persist for weeks. Severe disease requires 1-3 weeks of hospitalization, with renal and hepatic recovery over weeks to months. Late complications such as uveitis can appear weeks to months after the acute illness.

Yes. Avoid contact with floodwater and contaminated freshwater, wear waterproof boots and gloves for occupational water exposure, control rodents around homes, and vaccinate domestic animals. Doxycycline prophylaxis (200 mg weekly) protects high-risk responders, soldiers, and athletes during defined exposures.

Conjunctival suffusion — bilateral painless redness of the eyes without discharge — is one of the few highly characteristic clinical signs of leptospirosis, present in 30-90% of cases. It appears on day 2-4 of illness. Recognizing it in a febrile patient from an endemic region strongly raises suspicion and prompts empirical antibiotic therapy.

Yes. Doxycycline 100 mg orally twice daily for 7 days is the standard first-line oral treatment for mild and moderate leptospirosis in non-pregnant adults and children over 8. It shortens illness duration by 2-3 days and reduces shedding. Treatment is most effective within 5 days of symptom onset.

True relapse is uncommon with appropriate antibiotic therapy. Reinfection with a different serovar is possible because immunity is serovar-specific. Late immune complications such as uveitis are not a relapse of bacterial infection but a delayed antibody-mediated reaction.

Yes. Leptospirosis is endemic across coastal and high-rainfall regions of India, with the heaviest documented burden in Kerala, Tamil Nadu, Karnataka, Andaman & Nicobar Islands, Maharashtra, and Gujarat. Monsoon-season outbreaks recur each year, particularly during flooding.

Rats and other rodents carry leptospires chronically in their kidneys and shed live organisms in urine for months or years. Humans become infected when broken skin or mucous membranes contact contaminated water, mud, or rarely the animals themselves. Direct rat-bite transmission is rare but possible.

The Jarisch-Herxheimer reaction is a sudden worsening of symptoms — chills, fever, hypotension, worsening myalgia — within hours of the first dose of antibiotics in spirochetal infections. It occurs in 9-22% of leptospirosis cases and is managed with intravenous fluids, antipyretics, and short-course steroids in severe reactions.

Yes. Swimming, wading, kayaking, or rafting in lakes, rivers, and floodwater in endemic regions can transmit leptospirosis, especially through abrasions or mucous membranes. The Borneo Eco-Challenge outbreak (2000) infected approximately 80 of 304 participants. Chlorinated pools and saltwater do not transmit infection.

Leptospiral uveitis is a late immune complication that appears weeks to months after acute infection. It causes eye redness, blurred vision, photophobia, and floaters. Most cases respond to topical corticosteroids and cycloplegics; rarely systemic immunosuppression is needed. Untreated severe uveitis can cause vision loss.

Human vaccines are available in a few countries (Cuba, France, China, Japan) but are not widely licensed; they protect against specific local serovars and require frequent boosters. Veterinary vaccines for cattle, pigs, and dogs are widely used and reduce zoonotic transmission.

Yes, when diagnosed and treated promptly. Most patients recover fully with antibiotics. Severe disease with renal failure or pulmonary hemorrhage requires intensive care but is also curable in survivors. Late complications such as uveitis are treatable but may require months of topical therapy.

Both present with sudden fever, headache, and myalgia after monsoon-season exposure. Dengue causes retro-orbital pain, rash, plasma leakage, and is diagnosed by NS1 antigen or PCR. Leptospirosis adds conjunctival suffusion, calf myalgia, jaundice, and renal injury, and responds to doxycycline. Co-infection is well-documented during outbreaks.

Single-dose doxycycline 200 mg taken within 24-72 hours of a defined high-risk exposure (such as wading through floodwater for hours) reduces clinical illness in randomized trials. Routine prophylaxis is not indicated for brief or low-risk exposures. Consult local public-health guidance during major flooding.

Leptospires invade vascular endothelium and skeletal muscle, producing a vasculitis-like myositis that causes intense myalgia (often calf-predominant) and a marked rise in creatine kinase out of proportion to muscle injury. The pain is often the most prominent symptom and helps distinguish leptospirosis from other tropical fevers.