Main topic : One Health
Study of circulating Leptospira strains in humans and dogs in mainland France, between 2019-2021: an unsuspected diversity.
GARCIA-LOPEZ M. 1,2, LORIOUX C. 2, HARRAN E. 1, AYRAL F. 1, PICARDEAU M. 2, DJELOUADJI Z. 1, BOURHY P. 2
1 USC 1223-RS2GP, Laboratory of Leptospira and Veterinary Analysis, VetAgro Sup, University of Lyon, Marcy l'Etoile, France; 2 Biology of Spirochetes unit, National Reference Center for Leptospirosis, Institut Pasteur, Paris, France
Leptospirosis is a widespread zoonotic disease caused by pathogenic bacteria of the genus Leptospira. The incidence of the disease continues to increase in mainland France and has exceeded 600 cases per year1. The key potential maintenance hosts are rodents, mainly rats2, which excrete the bacteria in their urine and contaminate the environment. Humans and animals acquire the disease through direct contact with the urine of infected animals or indirect contact with contaminated environments. Both humans and dogs are susceptible hosts with comparable clinical manifestations ranging from febrile phase to multiple organ dysfunction3. Nevertheless, cases of leptospirosis in humans and dogs are most likely underestimated due to the lack of disease surveillance and limited epidemiological studies. Furthermore, the difficulty of obtaining isolated cultures limits our knowledge of the circulating strains. This study aimed to identify and describe the distribution of circulating pathogenic Leptospira ssp. in humans and dogs in mainland France, between 2019 and 2021, through the sequence polymorphism of the PCR products of the lfb1 gene4,5.
PCR assays for the detection of pathogenic Leptospira spp. were performed on samples from humans and dogs for which clinical manifestations of leptospirosis were reported between 2019 and 2021. Human samples were analyzed by the National Reference Center for Leptospirosis, and dog samples by the Veterinary Analysis Laboratory of VetAgro Sup. Only samples with a positive diagnosis were included in this study to identify the pathogenic Leptospira strain responsible for the acute infection. Sequencing of the lfb1 gene amplification product was performed on 170 samples, including 110 human samples and 60 canine samples. Epidemiology data in particular vaccination status were collected.
The phylogenetic analysis based on the lfb1 sequence revealed a high genetic diversity within three Leptospira species: L. interrogans with seven lfb1 species-groups (including 4 new lfb1 species-groups), L. kirschneri with two lfb1 species-groups (with 1 new lfb1 species-groups) in humans and dogs; and L. borgpetersenii represented by one lfb1 species-group in humans only. The lfb1 species-group L. interrogans 1, corresponds to serovar Icterohaemorrhagiae or Copenhageni, was frequently retrieved (n=98/170; 57.6%) among human and dog cases. Furthermore, almost 50% (n=29/60) of the infected dogs included in the study had a complete vaccination profile against Leptospira, mainly with L4 vaccines (serovars Icterohaemorrhagiae, Canicola, Grippotyphosa, and Pomona) or L3 vaccines (serovars Icterohaemorrhagiae, Canicola and Grippotyphosa).
Our study presents, for the first time, a global picture of the Leptospira strains responsible for acute infections in humans and dogs in mainland France. It also shows the identification of five previously undescribed lfb1 species-groups worldwide. We highly detected one lfb1 species-group, L. interrogans 1, in both human and dog samples, suggesting that rats may be a common source of infection. It is worth noting from this study that the canine vaccinations currently available in France are only partially effective in preventing the clinical form of the illness.