Leptospira diversity in animals and humans in Tahiti, French Polynesia

Leptospirosis is a highly endemic bacterial zoonosis in French Polynesia (FP). Nevertheless, data on the epidemiology of leptospirosis in FP are scarce. We conducted molecular studies on Leptospira isolated from humans and the potential main animal reservoirs in order to identify the most likely sources for human infection.Wild rats (n = 113), farm pigs (n = 181) and domestic dogs (n = 4) were screened for Leptospira infection in Tahiti, the most populated island in FP. Positive samples were genotyped and compared to Leptospira isolated from human cases throughout FP (n = 51), using secY, 16S and LipL32 sequencing, and MLST analysis. Leptospira DNA was detected in 20.4% of rats and 26.5% of pigs. We identified two Leptospira species and three sequence types (STs) in animals and humans: Leptospira interrogans ST140 in pigs only and L. interrogans ST17 and Leptospira borgpetersenii ST149 in humans and rats. Overall, L. interrogans was the dominant species and grouped into four clades: one clade including a human case only, two clades including human cases and dogs, and one clade including human cases and rats. All except one pig sample showed a unique L. interrogans (secY) genotype distinct from those isolated from humans, rats and dogs. Moreover, LipL32 sequencing allowed the detection of an additional Leptospira genotype in pigs, clearly distinct from the previous ones.Our data confirm rats as a major potential source for human leptospirosis in FP. By contrast to what was expected, farm pigs did not seem to be a major reservoir for the Leptospira genotypes identified in human patients. Thus, further investigations will be required to determine their significance in leptospirosis transmission in FP

Flowchart describing the steps of the molecular analysis.

<p>Methods used to detect and to identify <i>Leptospira</i> species and genotypes from samples collected in French Polynesia are detailed. Seven-loci MLST was attempted only for a selected subgroup of the animal and human samples successfully amplified on <i>secY</i> locus using MLST scheme #1.</p

Geographic localization of piggeries and rat sampling sites on Tahiti Island.

<p>The pig kidneys tested for <i>Leptospira</i> infection originated from 17 herds representing 16 farms. Rats were trapped at 12 sampling sites, including five farms from which pig kidneys originated.</p

Maximum-likelihood phylogenetic tree (model TN93+I; 1,000 replicates) inferred from <i>LipL32</i> gene (229-bp sequence).

<p>Clinical and animal samples from Tahiti are shown in light blue, clinical samples from other islands in French Polynesia (FP) in dark blue; referred to using identifiers accompanied by the host name. Corresponding GenBank accession numbers are reported in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005676#pntd.0005676.s005" target="_blank">S5 Table</a>. Published sequences included in the phylogeny are shown in black using the identified <i>Leptospira</i> species followed by GenBank accession numbers, the host species and the country of origin. The major genetic groups are highlighted with grey boxes (numbered 1 to 3). Bootstrap values higher than 70% are indicated by a dark circle. Black silhouettes represent host groups from FP (i.e. human, dog, pig or rat).</p

<i>Leptospira</i> detection and identification by host species.

<p>The prevalence of renal infection by <i>Leptospira</i> in farm pigs and rodents is based on RT-qPCR detection results. Infecting <i>Leptospira</i> species were determined by PCR, targeting either <i>secY</i>, <i>rrs</i> (16S) or <i>LipL32</i> gene in positive samples. The number of successful amplification for <i>secY</i> is provided. Based on the observed diversity within the <i>secY</i> gene, MLST amplifications were attempted on a subset of positive samples; the number of successful complete MLST on seven (or six) loci is given.</p