Terrestrial leeches in Madagascar: Their phylogeny, role as biodiversity indicators and potential as tools for detecting Yersinia pestis reservoirs via iDNA analysis

Details

Supervisors

Batoko, Henri ; Tortosa, Pablo

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie, à finalité approfondie

Abstract

Plague, a globally relevant zoonosis, re-emerges seasonally in Madagascar, suggesting a persistent biological reservoir. However, factors driving the maintenance of Yersinia pestis in the environment remain poorly understood. This study explores the phylogeny and ecology of Malagasy terrestrial leeches and assesses their potential as biodiversity indicators and tools for detecting Y. pestis reservoirs through iDNA analysis. Morphological identification of sampled leeches proved inconclusive, but most appeared to belong to a single species, with two outliers showing distinct traits. Molecular barcoding of CO1 sequences failed to confidently identify species, yet a phylogenetic tree inferred by Maximum Likelihood revealed two distinct monophyletic groups, likely representing undescribed species or distinct local lineages. These findings are consistent with our morphological and molecular identifications, and collectively, they highlight the lack of knowledge regarding these hematophagous ectoparasites. Next, host identification was performed using the 16S mitochondrial locus. Despite employing human blocking primers, the most frequently detected host was Homo sapiens, indicating insufficient primer concentration. Nonetheless, native (Boophis entingae, Tenrec ecaudatus), introduced (Potamochoerus sp.) and invasive species (Rattus sp.) were detected. The frequent detection of Rattus rattus, a known plague carrier, demonstrates the potential of leech-derived iDNA in wildlife surveillance for zoonotic pathogens. Finally, attempts to detect Y. pestis via two-step real-time PCR and conventional PCR were inconclusive, underscoring the need for improved protocols. For one sample, the initial step yielded a positive result whereas the subsequent step returned a negative result, indicating the potential presence of a bacterial species other than Yersinia pestis. However, the conventional PCR yielded inconclusive results, precluding the sequencing and identification of the pathogen. Despite the uncertainty in the possibility of detecting Y. pestis, these findings highlight the promise of leech-derived iDNA for both biodiversity assessments and pathogen surveillance.