A pilot study for the identification of biomarkers of Ehrlichia ruminantium infection by natural host

Heartwater, caused by the Rickettsiales Ehrlichia ruminantium, is one of the most important tick-borne diseases of livestock in Africa, but also in the Caribbean from where it threatens the American mainland. All domestic and wild ruminants can be infected by E. ruminantium, a small pleomorphic gram-negative obligate intracellular bacterium invading the cytoplasm of vascular endothelial cells. Clinical diagnosis of heartwater is based on the presence of Amblyomma sp. ticks, nervous signs, and presence of transudates in the pericardium and thorax on post-mortem examination, and efficient molecular diagnostics allow reliable heartwater confirmation but not early detection. The objective of the present study was to evaluate modifications in serum composition in animals infected by E. ruminantium and define new diagnostic biomarkers. For this, sera from goats experimentally infected by intravenous injection of E. ruminantium cultured in bovine aortic endothelial cells in vitro were sampled. Sera at Day 0 and Day 14 post-infection (occurrence of clinical signs) were pre-fractionated by SDS-PAGE and analysed by shotgun next-generation proteomics by means of high-throughput analysis of peptides with a Q-Exactive HF mass spectrometer incorporating an ultra-high-field Orbitrap analyzer. Preliminary data obtained against the Capra hircus and Ehrlichia ruminantium theoretical molecular databases evidenced 6 and 2 proteins of interest for which abundances were increased or decreased, respectively, at Day 14. These proteins could represent a molecular signature of E. ruminantium infection. Here, we demonstrated the relevance of such proteomic approach to propose candidate diagnostic biomarkers of heartwater. Further investigations will be performed for monitoring more precisely the whole kinetics of E. ruminantium infection for delineating biomarkers for early diagnosis. (Texte intégral)