What is Leptospirosis?
Leptospirosis is a zoonotic bacterial disease caused by spirochetes of the genus Leptospira. It is considered the most common worldwide infectious zoonosis, with cases reported across all continents except Antarctica. The disease affects both animals and humans, with rodents, cattle, dogs, and other mammals serving as reservoir hosts. The bacteria are shed in the urine of infected animals and can survive in warm, moist environments for weeks to months, making water and soil contaminated with infected animal urine the primary routes of transmission to humans.
How People Get Infected
Transmission occurs when bacteria in contaminated water or soil enter the body through cuts or scratches in the skin, through mucous membranes of the eyes, nose, or mouth, or, rarely, through ingestion of contaminated food or water. Activities that place people at high risk include:
• Agricultural work, especially rice farming and sugarcane harvesting
• Wading or swimming in contaminated freshwater (rivers, lakes, ponds, floodwater)
• Occupational exposure in veterinarians, farmers, slaughterhouse workers, and sewage workers
• Recreational activities like whitewater rafting, kayaking, and triathlons in tropical regions
• Contact with animals or animal urine in endemic areas
In Thailand, leptospirosis is a significant public health concern, particularly in rural agricultural communities during the rainy season. The northern and northeastern regions of Thailand report the highest incidence rates, with cases closely correlated with flooding and heavy rainfall.
Symptoms: From Mild Flu-like to Life-Threatening
Leptospirosis is known as “the great imitator” because its symptoms mimic many other diseases. The incubation period ranges from 2 to 30 days, typically 7 to 14 days.
Classic (anicteric) leptospirosis — accounting for about 90% of cases — presents as a sudden-onset flu-like illness:
• Sudden high fever: Often reaching 39°C to 40°C (102°F to 104°F)
• Chills and rigors: Often sudden and dramatic
• Severe muscle aches: Particularly affecting the calves, lower back, and thighs — calf tenderness is a classic finding
• Severe headache: Often frontal and frontal-temporal
• Nausea, vomiting, and diarrhea: Gastrointestinal symptoms are common
• Rash: Macular or petechial, appearing in some cases
• Conjunctival suffusion: Red eyes without purulent discharge — this is a highly characteristic finding of leptospirosis
• Jaundice: Yellowing of the skin and eyes (absent in anicteric form)
Severe leptospirosis (Weil’s disease) occurs in approximately 5% to 10% of cases and can be fatal:
• Severe jaundice with liver failure
• Acute kidney injury requiring dialysis
• Pulmonary hemorrhage — diffuse alveolar hemorrhage can be rapidly fatal
• Meningitis and meningoencephalitis
• Cardiac arrhythmias and myocarditis
• Disseminated intravascular coagulation (DIC)
• Multiorgan failure and death (mortality in Weil’s disease is 5% to 15%, and up to 50% in severe pulmonary hemorrhagic syndrome)
Diagnosis
Diagnosis is challenging because early symptoms overlap with many tropical diseases. Key diagnostic tools include:
• Culture: The definitive diagnostic method, but Leptospira grows slowly (up to 13 weeks) and requires specialized media, making it impractical for acute management
• PCR: Detects Leptospira DNA in blood (first week) and urine (second week onward); provides rapid results
• Microscopic Agglutination Test (MAT): The gold standard serological test, detecting agglutinating antibodies; requires paired sera showing a four-fold rise in antibody titer
• Rapid diagnostic tests: IgM-based ELISA and lateral flow assays provide faster results but may have variable sensitivity
• Complete blood count: May show thrombocytopenia and elevated C-reactive protein
• Chemistry panel: Elevated creatinine (kidney injury), bilirubin, and liver enzymes
Leptospirosis must be differentiated from malaria, typhoid fever, dengue fever, scrub typhus, viral hepatitis, and other febrile illnesses — all of which are common in tropical Thailand.
Treatment
• Mild disease: Oral doxycycline (100 mg twice daily for 7 days) or oral amoxicillin/ampicillin. Most patients can be treated at home with antibiotics, fluids, and supportive care.
• Severe disease: Intravenous ceftriaxone (1-2 g daily) or IV penicillin G. Hospitalization is essential for close monitoring of renal function, fluid balance, and respiratory status.
• Supportive care: Aggressive fluid and electrolyte management, renal replacement therapy (dialysis) if needed, and careful monitoring for pulmonary hemorrhage.
Early antibiotic treatment — even within the first five days of illness — shortens the clinical course, reduces complications, and decreases the duration of bacteremia and bacterial shedding.
Prevention
• Avoid contact with potentially contaminated water: Especially during and after flooding. Do not swim or wade in floodwater, rivers, or ponds in endemic areas.
• Wear protective clothing: Waders, boots, and gloves when working in waterlogged soil or with animals
• Cover wounds: Use waterproof dressings on any cuts or abrasions before contact with potentially contaminated water
• Antibiotic prophylaxis: Doxycycline 200 mg weekly during high-risk activities (e.g., rafting, military exercises in endemic areas)
• Control rodents: Reduce rodent populations around homes and workplaces
• Vaccination: Vaccines are available in some countries for high-risk occupational groups, but no vaccine is widely available globally
Dr. Kijakarn emphasizes the connection between flooding and leptospirosis in Thailand. “Every major flood in Thailand is followed by a spike in leptospirosis cases. We see farmers and flood cleanup workers presenting with high fever, muscle pain, and jaundice. Anyone who has been wading in floodwater and develops fever should seek medical care immediately and specifically mention their water exposure — this dramatically speeds up diagnosis and treatment.”
This article is for general information only and does not replace professional medical advice. If you are experiencing symptoms, please consult a healthcare provider.
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