Human Leptospirosis on Reunion Island, Indian Ocean: Are Rodents the (Only) Ones to Blame?

<div><p>Background</p><p>Although leptospirosis is a zoonosis of major concern on tropical islands, the molecular epidemiology of the disease aiming at linking human cases to specific animal reservoirs has been rarely explored within these peculiar ecosystems.</p><p>Methodology/Principal Findings</p><p>Five species of wild small mammals (n = 995) as well as domestic animals (n = 101) were screened for <i>Leptospira</i> infection on Reunion Island; positive samples were subsequently genotyped and compared to <i>Leptospira</i> from clinical cases diagnosed in 2012–2013 (n = 66), using MLST analysis. We identified two pathogenic species in human cases, namely <i>Leptospira interrogans</i> and <i>Leptospira borgpetersenii</i>. <i>Leptospira interrogans</i> was by far dominant both in clinical samples (96.6%) and in infected animal samples (95.8%), with <i>Rattus spp</i> and dogs being its exclusive carriers. The genetic diversity within <i>L</i>. <i>interrogans</i> was apparently limited to two sequence types (STs): ST02, identified among most clinical samples and in all rats with complete MLST, and ST34, identified in six humans, but not in rats. Noteworthy, <i>L</i>. <i>interrogans</i> detected in two stray dogs partially matched with ST02 and ST34. <i>Leptospira borgpetersenii</i> was identified in two clinical samples only (3.4%), as well as in cows and mice; four haplotypes were identified, of which two seemingly identical in clinical and animal samples. <i>Leptospira borgpetersenii</i> haplotypes detected in human cases were clearly distinct from the lineage detected so far in the endemic bat species <i>Mormopterus francoismoutoui</i>, thus excluding a role for this volant mammal in the local human epidemiology of the disease.</p><p>Conclusions/Significance</p><p>Our data confirm rats as a major reservoir of <i>Leptospira</i> on Reunion Island, but also pinpoint a possible role of dogs, cows and mice in the local epidemiology of human leptospirosis. This study shows that a comprehensive molecular characterization of pathogenic <i>Leptospira</i> in both clinical and animal samples helps to gaining insight into leptospirosis epidemiology within a specific environmental setting.</p>