What is leptospirosis?

Leptospirosis is a bacterial zoonotic infection caused by pathogenic Leptospira spirochaetes — transmitted from animal urine (predominantly rats, cattle, pigs and dogs) to humans through direct contact with infected urine or water/soil contaminated with infected animal urine. Most infections (approximately 90%) cause mild flu-like illness; 10% cause severe disease (Weil's disease) with jaundice, kidney failure and bleeding, which can be fatal without treatment.

How is leptospirosis transmitted?

Leptospira enters the human body through: cuts or abrasions in the skin; mucous membranes (eyes, nose, mouth); and potentially intact but water-softened skin during prolonged immersion. Common exposure routes: wading through flood water contaminated with rat urine; working in rice paddies or sugarcane fields; recreational water activities in contaminated rivers, lakes; handling animals or their products; and occupational exposure for sewer workers and veterinarians.

Why is leptospirosis so underdiagnosed?

Leptospirosis is one of the most underdiagnosed infections because: it mimics dengue, malaria, typhoid and influenza in its early stages (fever, headache, myalgia); the definitive diagnostic test (MAT) requires specialised laboratories with live Leptospira cultures — unavailable in most endemic settings; rapid diagnostic tests are commercially available but have limited sensitivity; and healthcare workers in endemic areas often do not consider leptospirosis in the differential diagnosis. WHO estimates the actual burden may be 10 times higher than reported.

What are the symptoms of leptospirosis?

Leptospirosis classically has two phases. Phase 1 (leptospiraemic, days 1-7): abrupt onset fever, severe headache, myalgia (particularly calf muscles — characteristic), conjunctival suffusion (bloodshot eyes without discharge), and sometimes skin rash. Most patients recover. Phase 2 (immune/late phase, days 7-14): approximately 10% develop Weil's disease — jaundice, acute kidney injury, pulmonary haemorrhage (haemoptysis, respiratory failure), coagulopathy and myocarditis. Weil's disease is fatal in 5-40% of untreated cases.

How is leptospirosis treated?

Treatment: doxycycline 100 mg twice daily (7 days) for mild disease; intravenous penicillin G or ampicillin/amoxicillin for severe disease. Early antibiotic therapy reduces severity and duration. IV penicillin in severe leptospirosis may reduce the risk of oliguria. Supportive care (fluid management, dialysis for renal failure, ventilation for pulmonary haemorrhage, correction of coagulopathy) is critical in Weil's disease.

What is the role of rats in leptospirosis?

Rats (Rattus norvegicus, Rattus rattus) are the most important reservoirs of leptospirosis globally — chronically infected in their kidneys without illness, shedding massive amounts of Leptospira in urine. Rat populations in urban slums, agricultural areas and flood-prone zones are the primary source of human exposure. Rat control — population management, food storage, sanitation — is an effective prevention strategy, particularly in urban settings.

How does flooding cause leptospirosis outbreaks?

Flooding is the most powerful amplifier of leptospirosis transmission: floodwater disperses rat and animal urine over wide areas; contaminated water contacts skin and mucous membranes during wading; clean water infrastructure is disrupted; and flood response activities (clean-up, sandbag placement) force people into contact with contaminated water. Post-flood leptospirosis outbreaks are well-documented globally — Philippines, Sri Lanka, Brazil and Central America. Climate change, by intensifying flooding, is expanding leptospirosis risk.

Can leptospirosis be prevented?

Prevention strategies: doxycycline prophylaxis (200 mg weekly) for high-risk occupational exposure; personal protective equipment (rubber boots, gloves) for workers in endemic settings; rat control in urban environments; safe water supply and sanitation; vaccination of livestock and companion animals (reduces reservoir); and post-flood prophylaxis during outbreak response. Human vaccines are available in some countries (Cuba, China, Japan) but are not widely used globally.

What is the One Health link?

Leptospirosis is a paradigm case for One Health: it exists at the interface of animal reservoirs (rats, cattle, pigs, dogs), environmental contamination (water, soil), and human exposure through agriculture, flooding and occupational contact. Effective control requires coordination across human health (clinical management, surveillance), veterinary (animal vaccination, reservoir management), and environmental (WASH, flood management, rat control) sectors.

How does leptospirosis relate to climate change?

Climate change is projected to increase leptospirosis incidence through: more frequent and intense flooding events; rising temperatures extending the geographic range of Leptospira survival in the environment; and intensified agriculture in warm, humid regions. The WHO has identified leptospirosis as one of the climate-sensitive diseases most likely to increase in burden with projected warming and altered precipitation patterns.

How does GMJ News cover leptospirosis?

GMJ News covers WHO leptospirosis burden estimates, flood-associated outbreak reports, climate-leptospirosis links and One Health prevention approaches. Leptospirosis is present in the Caucasus region through agricultural and flood exposures — a direct concern for PHIG's One Health and environmental health agenda.

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Leptospirosis

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Leptospirosis is the world's most widespread zoonotic disease — affecting an estimated 1 million people per year and causing approximately 59,000 deaths, predominantly in tropical and subtropical regions where flooding, agricultural work and rat contact are common (WHO). Caused by Leptospira bacteria transmitted through animal urine (rats, cattle, pigs) contaminating water and soil, leptospirosis disproportionately affects agricultural workers, urban slum dwellers and people exposed to flooding. Climate change — by intensifying flood events — is increasing leptospirosis transmission globally.

Key messages

Most widespread zoonosis

Leptospirosis is the world's most widespread zoonotic disease — infecting an estimated 1 million people per year and killing approximately 59,000. It is caused by Leptospira bacteria transmitted through animal urine contaminating water and soil (WHO).

Flood-linked

Flooding dramatically amplifies leptospirosis transmission — dispersing animal urine over wide areas, contaminating water sources, and forcing people into flood water contact. Climate change — increasing flood frequency — is expanding leptospirosis risk globally.

Agricultural workers at risk

Leptospirosis predominantly affects: rice paddy farmers, sugarcane harvesters and other agricultural workers (foot/leg immersion in contaminated soil and water); urban slum dwellers (rat urine contaminating floodwater); recreational water users; sewer workers; and veterinarians.

Weil's disease

Severe leptospirosis — Weil's disease — causes jaundice, renal failure, pulmonary haemorrhage and multi-organ failure with a case fatality rate of up to 40% without treatment. Early antibiotic therapy is life-saving.

Doxycycline treatment and prophylaxis

Doxycycline is both treatment (first-line for mild leptospirosis) and post-exposure prophylaxis (single dose after known exposure). Penicillin or ampicillin IV are used for severe disease.

Highly underdiagnosed

Leptospirosis is massively underdiagnosed — it mimics dengue, malaria and other febrile illnesses, and definitive diagnosis (MAT serology or culture) requires specialised laboratories absent in most endemic settings. The true burden may be 10 times higher than reported.

Key statistics

cases/year (estimated)

WHO

59K

deaths/year

WHO

10x

actual burden above reported

WHO research

Up to 40%

CFR in severe Weil's disease

WHO

Worldwide

except in Antarctica — distributed globally

WHO

Flooding

primary amplifying factor for outbreaks

WHO/Lancet

Estimated leptospirosis cases per year by region (thousands) — WHO/ILRI

Source: WHO/ILRI global burden estimates. Asia-Pacific carries the largest burden.

Glossary of key terms

Leptospira
WHOA genus of spiral bacteria (spirochaetes) comprising over 300 pathogenic serovars. Maintained in the environment by chronically infected animal reservoirs — rats, cattle, pigs, dogs. Humans are accidental dead-end hosts infected through skin contact with contaminated water or soil.

Weil's disease
WHO/ClinicalSevere leptospirosis — characterised by the triad of jaundice, acute kidney injury and bleeding (including pulmonary haemorrhage). Case fatality rate up to 40% without treatment. Requires IV antibiotics and ICU support.

MAT (microscopic agglutination test)
WHOThe gold-standard serological diagnostic test for leptospirosis — detecting antibodies in patient serum that agglutinate live Leptospira antigens. Requires live Leptospira cultures and is available only in specialised laboratories.

Conjunctival suffusion
WHO/ClinicalRedness of the conjunctiva (eye whites) — a characteristic early clinical feature of leptospirosis, distinguishing it from conjunctivitis (which has discharge). Seen in approximately 40% of leptospirosis cases in the first week.

Doxycycline prophylaxis
WHO/CDCA single 200 mg oral dose of doxycycline taken within 48-72 hours of exposure (known immersion in contaminated water during an outbreak) reduces leptospirosis risk by approximately 95%. Used for flood relief workers and others with known occupational exposure.

Canicola fever
WHOLeptospirosis caused by Leptospira canicola — transmitted by dogs. Dogs are significant reservoirs in urban settings. Canine leptospirosis vaccination reduces transmission to humans.