Leptospirosis is contracted in aquatic environments contaminated by the urine and excrement of rats. Michael Eaton / stock.adobe.com
This infectious disease is transmitted from rats to humans through contact with water and has proliferated in recent years due to heavy rains.
A worrying increase in cases of leptospirosis in the French overseas territories. In particular on Reunion Island where 165 cases and three deaths linked to this disease were recorded in 2022, compared to 140 cases in 2021. To combat the proliferation of this bacterium transmitted from rats to humans, the Reunionese authorities have launched a second deratting campaign from March 17 until the end of May.
Leptospirosis is caused by leptospira bacteria that thrive in warm, moist environments, where they can survive for up to several weeks. The disease is contracted on contact with water (fresh water or muddy soil) contaminated with the urine and excrement of mammals, mainly rats. Humans can be infected only if they have skin lesions – bacteria do not cross healthy skin.
Rainy season favorable to contamination
This infectious disease experiences an upsurge each year during the rainy season, from January to May. However, since 2016, an unprecedented increase in the number of cases has been observed in Reunion: from 45 cases in 2016 to 165 cases in 2022. This is partly explained by extreme rainfall caused by global warming. “With the recent heavy rains, a further increase in the number of cases is expected in the coming weeks.“, warns the Ministry of Health at Figaro.
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«The rainy season is the period most at risk“, recalled the Regional Health Agency, quoted by France Info. “This period is particularly favorable for soil leaching responsible for the dispersion of leptospires in the environment. It also has temperature and humidity conditions conducive to the survival of the bacteria in humid environments.“, continues the Ministry of Health.
Diagnostic issues
However, other factors may have contributed to the increase in contamination on Reunion Island. Notably “an improvement in the reporting of leptospirosis cases in connection with the awareness of health professionals“, reports the ministry. If this disease has been known for more than a century by scientists, “we are witnessing real diagnostic problems because the symptoms are close to those of the flu (high fever, muscle aches and strong headaches)”, points out Mathieu Picardeau, head of the national reference center for leptospirosis at the Institut Pasteur.
“This rise in cases is worrying because not diagnosing a patient with leptospirosis increases their chances of developing severe forms of the disease..” The first symptoms appear on average one to two weeks after contamination. But “the disease can worsen four to five days after the first signs and extend to the meninges, liver, kidneys, lungs…“Alerts the ministry. In 2022 in Réunion, 7 cases out of 10 required hospitalization and 1 case out of 4 was placed in intensive care.
According to Mathieu Picardeau, scientists identify a million severe cases in the world each year, “but this figure is most likely underestimated due to lack of monitoring, especially in Africa“. And at least 60,000 people a year die from this disease, adds the expert. The latter nevertheless wishes to reassure:When the diagnosis is made in time, treatment with antibiotics is very effective.»
Low risk in mainland France
Reunion is not the only French overseas territory to be affected by this increase in contamination. This is the case of New Caledonia, whose number of cases rose from 65 in 2019 to 265 in 2022. Elsewhere in the world, leptospirosis is present in tropical islands. “The highest incidences are recorded in Southeast Asia, the Pacific and Indian Oceans“says Mathieu Picardeau.
But what about metropolitan France? According to the Institut Pasteur researcher, “there are on average 700 cases of leptospirosis per year in mainland France“. With the garbage collectors’ strike in the capital in recent weeks, mountains of garbage litter the streets and attract rats.
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The question of an increase in contamination then arises. “There is no proven health riskassures the Ministry of Healthbecause city sidewalks are not a humid environment favorable to the survival or proliferation of leptospires. Same analysis on the side of Mathieu Picardeau who declares not to observe any evolution in this direction and adds that “the epidemic peak is in summer when people practice water activities».