Leptospirosis is caused by the bacterium Leptospira interrogans senso lato. This bacterium survives well in the outside environment (freshwater, muddy soil, etc.), which facilitates contamination.
The incubation period is from 4 to 14 days. This disease has a number of clinical forms, ranging from flu-like syndrome to multi-organ involvement with hemorrhagic syndrome. In its moderate form, the disease starts with high fever and shivering, headache, muscle pain and generalized joint pain. It may go on to affect the kidneys, liver, meninges or lungs. There are no distinctive symptoms, but conjunctival jaundice and myalgia are particularly common. Serious forms (hemorrhagic jaundice or Weil's disease) bring acute kidney failure, neurological disorders (seizures, coma) and pulmonary and gastrointestinal hemorrhaging with varying degrees of severity. Convalescence is lengthy, but usually without sequelae. Late ocular complications (uveitis, keratitis) may occur.
A diagnosis can be confirmed by culture or – even more effectively – by gene amplification during the first week after the onset of high fever, or by serology from the second week of the disease onwards.
This is a disease seen throughout the world, mainly in tropical regions. In mainland France it affects around 300 people annually, which indicates an annual incidence of 0.4 to 0.5 per 100,000 inhabitants. The incidence is from 100 to 1000 times higher in tropical regions, such as the French overseas collectivities or many Latin American and Southeast Asian countries. The number of serious cases of leptospirosis seen annually throughout the world is estimated at over one million, with a case fatality rate above 10%. The disease has a clear seasonal pattern, with summer and autumn peaks linked to hot weather and rainfall.
Certain occupations (farmers, livestock breeders, sewage workers, refuse collectors, etc.) and people who take part in water sports (swimming, canoeing, kayaking, fishing, hunting, canyoneering, etc.) are particularly at risk. In humans, the bacterium enters the body mainly through damaged skin or the mucous membranes. The animal reservoir is highly diversified and, in addition to rodents and insectivores, includes livestock such as cattle, horses or pigs – in which infection is a frequent occurrence and results in significant financial losses – and domestic animals such as dogs. All these animals transmit leptospirosis via their urine. Entire flocks and herds become contaminated from just a few carrier individuals. Epidemiology varies between geographical regions, depending on the ecosystem and living conditions.
Treatment and prevention
The serious forms require hospitalization. Treatment is based on intensive care. Early administration of antibiotics (amoxicillin, cephalosporin and cyclins) reduces the risk of complications, shortens disease progression, relieves symptoms and limits renal damage. In terms of prevention, collective measures to control rat populations and effluents from factory farming systems and to drain flooded areas might be effective but are difficult to implement. A monovalent human vaccine is available in France, solely to workers with a high level of exposure (sewage workers and refuse collectors). A bivalent vaccine for dogs is widely used in France.
At the Institut Pasteur
Fundamental research into Leptospira is being undertaken by the Biology of Spirochetes Unit, which also includes the National Reference Center for Leptospirosis and FAO/WHO Collaborating Center for Epidemiology of Leptospirosis. A number of leptospiral identification methods have been developed. Epidemiological surveys have also been undertaken in endemic regions (the island of Mayotte, the Antilles, etc.). Lastly, scientists at the Institut Pasteur have also identified several virulence factors in the bacterium responsible for this disease.
Surveillance and Public Health : National Reference Center for Leptospirosis led by Mathieu Picardeau