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Mycoplasma equirhinis, a neglected player in equine respiratory disorders ?
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Edité par CCSD -
International audience. Respiratory disorders are responsible for poor performance in racehorses and for overall significant economic problems in the equine industry. Bacteria belonging to the Mycoplasma (M.) genus have been regularly reported in up to 15% of clinical specimens in different countries, but their clinical contribution remains unclear.To assess their role, a detection / isolation protocol combining culture and post-enrichment PCRs was optimized and used on 1,948 respiratory samples collected from 1,764 horses in France over the 2020-2022 period. The prevalence of mycoplasmas was refined to 16.1%, with a predominance of M. equirhinis (Mequi) species (85.3%). We further used a clinical scoring, a risk factor analysis as well as a test for association with other bacteria and viruses to improve our understanding of the clinical role of Mequi. In contrast to the pattern of primary pathogens, Mequi prevalence remained steady whatever the clinical score. Nonetheless, in presence of Streptococcus equi subsp. zooepidemicus (S. zoo) or viruses like EHV-5 the prevalence of Mequi was significantly increased. CO-infection between Mequi and S. zoo was associated with, on average, a significantly higher load of S. zoo. These results indicate that Mequi is not a primary pathogen but could contribute to clinical signs in association with other microbes. In bronchoalveolar lavages, the detection of Mequi was associated with neutrophilmediated inflammation, suggesting it could participate in an inappropriate immune response, similar to that observed in equine asthma. This is consistent with the fact that Mequi was more frequently isolated in racehorses and stabled horses, two favouring factors for asthma.Through comparison of 24 genomes, we further showed that Mequi is a highly homogeneous species, with only a few mobile genetic elements like the M. arginini-like ICE (Integrative Conjugative Element) and a M. arthritidis-like prophage. The repertoire of genes putatively associated to virulence was rather limited to cytoadherence and immune escape, similarly to its closest phylogenetic neighbour, M. hominis. In conclusion, Mequi could play a part in the equine respiratory disease complex, in association with other microbes, essentially through dysregulation of the host immune response, as is well known for other mycoplasma species in other respiratory complexes
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