Leptospirosis

Leptospirosis is a blood infection caused by bacteria of the genus Leptospira that can infect humans, dogs, rodents, and many other wild and domesticated animals. Signs and symptoms can range from none to mild (headaches, muscle pains, and fevers) to severe (bleeding in the lungs or meningitis). Weil's disease ( VILES), the acute, severe form of leptospirosis, causes the infected individual to become jaundiced (skin and eyes become yellow), develop kidney failure, and bleed. Bleeding from the lungs associated with leptospirosis is known as severe pulmonary haemorrhage syndrome. More than 10 genetic types of Leptospira cause disease in humans. Both wild and domestic animals can spread the disease, most commonly rodents. The bacteria are spread to humans through animal urine or feces, or water or soil contaminated with animal urine and feces, coming into contact with the eyes, mouth, or nose, or breaks in the skin. In developing countries, the disease occurs most commonly in pest control, farmers, and low-income people who live in areas with poor sanitation. In developed countries, it occurs during heavy downpours and is a risk to pest controllers, sewage workers, and those involved in outdoor activities in warm and wet areas. Diagnosis is typically by testing for antibodies against the bacteria or finding bacterial DNA in the blood. Efforts to prevent the disease include protective equipment to block contact when working with potentially infected animals, washing after contact, and reducing rodents in areas where people live and work. The antibiotic doxycycline is effective in preventing leptospirosis infection. Human vaccines are of limited usefulness; vaccines for other animals are more widely available. Treatment when infected is with antibiotics such as doxycycline, penicillin, or ceftriaxone. Mortality from severe disease forms, Weil's disease and severe pulmonary haemorrhage syndrome, is high (>10% and >50%, respectively) even when optimal treatment is provided. When the lungs are involved, the risk of death increases to the range of 50–70%.

Environmental and One Health considerations Leptospirosis is a known One Health issue because its transmission involves complex interactions among humans, animals, and the environment. Transmission commonly occurs through water when it is contaminated with urine from infected animals like rodents and livestock. Environmental factors such as heavy rainfall, flooding, and poor sanitation significantly increased the risk of leptospirosis transmission by allowing the spread of contaminated water. Additionally, urbanization and inadequate waste management promote the growth of rodent populations, which act as primary reservoirs for the bacteria. Climate change is associated with a higher incidence of leptospirosis because extreme weather events create a suitable environment for outbreaks. The One Health approach highlights the significance of coordinated efforts among human health, veterinary health, and environmental health, and environmental management sectors to prevent and control the disease. Leptospirosis disproportionately affects populations in environments where exposure is unavoidable, particularly in regions with inadequate drainage, poor sanitation, and frequent flooding. In these environments, individuals are routinely exposed to contaminated soil and water, which increases infection risk. These patterns underscore the role of environmental conditions and structural inequalities in shaping disease distribution. Beyond direct transmission from animal reservoirs, growing evidence indicates that Leptospira can persist in environmental reservoirs such as soil and freshwater systems, thereby extending the window of exposure beyond intermediate contamination events. Studies show that the organism survives for prolonged periods in moist environments, with factors such as temperature, pH, and nutrient availability affecting its viability. This persistence complicates traditional transmission models by enabling indirect exposure pathways that do not require recent animal contact.

Public health interventions and One Health implementation Effective control of leptospirosis requires coordinated interventions across human, animal, and environmental health sectors. Public health strategies include surveillance systems to monitor outbreaks, particularly in regions prone to flooding and poor sanitation. Early diagnosis and improved laboratory capacity are essential for timely case identification and response. Animal health interventions include vaccination of livestock and domestic animals, as well as rodent control programs aimed at reducing reservoir populations. In agricultural and occupational settings, the use of protective equipment can reduce exposure risk among workers. Environmental interventions focus on improving sanitation infrastructure, ensuring safe water management, and implementing waste control measures to limit contamination of soil and water. Urban planning and drainage improvements are also important in reducing standing water that facilitates bacterial survival. The One Health framework emphasizes interdisciplinary collaboration among healthcare providers, veterinarians, environmental scientists, and policymakers to improve prevention and outbreak response. An estimated one million severe cases of leptospirosis in humans occur every year, causing about 58,900 deaths. The disease is most common in tropical areas of the world, but may occur anywhere. Outbreaks may arise after heavy rainfall. The disease was first described by physician Adolf Weil in 1886 in Germany. Infected animals may have no, mild, or severe symptoms. These may vary by the type of animal. In some animals, Leptospira live in the reproductive tract, leading to transmission during mating.

Signs and symptoms

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