What are the causes?
Leptospirosis is a disease caused by Leptospira bacteria (such as the species Leptospira interrogans). They are spread via urine and survive relatively easily in outdoor environments, especially fresh water and muddy ground. The main animals capable of transmitting the disease are rodents and insectivores, as well as livestock including cattle, horses and pigs. Pets such as dogs may also carry the bacteria.
How does the disease spread?
In humans, the bacteria generally enter the body through wounds or mucosa after exposure to an environment contaminated by the urine of animal reservoirs. Leptospirosis may be contracted anywhere in the world, but the risks are much higher in tropical regions. More people are affected in summer and autumn in temperate countries, or during the rainy season in tropical regions.
What are the symptoms?
After an incubation period of 5 to 14 days, symptoms include high fever with chills, headache, very red eyes, muscle and joint pain, and sometimes a cough.
Several clinical forms, ranging from flu-like symptoms to multiple organ failure with hemorrhagic syndrome, have been described.
In the moderate form, the first symptoms are high fever with chills, headache and diffuse muscle and joint pain. But the disease can develop into kidney or liver failure, meningitis or pulmonary symptoms. Hemorrhage occurs in 20% of cases. There are no specific telltale symptoms, but yellow eyes and myalgia (muscle pain) are particularly common.
Weil's disease refers to a severe form of leptospirosis that causes acute kidney failure, neurological symptoms (convulsions or coma) and sometimes severe gastrointestinal or pulmonary hemorrhage. Recovery time is long but most patients recover fully with no long-term effects. Ocular complications including uveitis or keratitis may occur at a later stage.
In this form, the disease is potentially fatal.
How is leptospirosis diagnosed?
Leptospirosis may be diagnosed by PCR to identify the bacteria in the blood and/or urine in the first days of the disease, or by serological assay (IgM ELISA) from the sixth day after the onset of symptoms.
What treatments are available?
Moderate forms of leptospirosis can clear up on their own without any after-effects, but the use of antibiotics may be recommended. Patients with Weil's disease require intensive care in hospital, with the administration of antibiotics.
How can leptospirosis be prevented?
Effective preventive measures include rat extermination, draining flooded areas and monitoring water from factory farms, but these can be hard to implement. Personal protective equipment (gloves, goggles and boots) is recommended for people who may be exposed to Leptospira.
It is also important to avoid swimming in fresh water if you have any open wounds, especially after heavy rainfall, when there can be run-off from banks and soil.
In France, a human vaccine is available solely for workers with high exposure, such as farmers, livestock breeders, sewage workers and garbage collectors. A specific vaccine for dogs is widely used in France. There are also vaccines for farm animals.
Who is affected?
Leptospirosis is a disease that occurs worldwide but especially in tropical regions. In mainland France, it affects 600 to 700 people each year, an annual incidence of 1/100,000 people.
The incidence is 50 or 100 times higher in tropical regions, such as the French overseas territories or countries in Latin America or South-East Asia.
The number of severe cases of leptospirosis worldwide every year is estimated to be over a million, with a case fatality rate above 10%. The disease has a clear seasonal pattern, with peaks during the rainy season in tropical regions and during the summer and autumn in temperate countries, when people are more likely to swim in fresh water.
How many people are affected?
People in certain occupations (farmers, livestock breeders, sewage workers and garbage collectors) and people who engage in water sports (outdoor swimming, canoeing, kayaking, fishing, hunting and canyoneering) are particularly at risk. In humans, the bacteria mainly enter through broken skin or mucosa. The animal reservoir is highly diverse – as well as rodents and insectivores, it includes livestock such as cattle, horses and pigs, which are frequently infected, resulting in significant financial losses, and also pets like dogs. All these animals spread leptospirosis via their urine. Entire herds can become infected from just a few individual carriers. Epidemiology varies from one geographical region to the next depending on the ecosystem and living conditions.
November 2024