Ehrlichia ruminantium: The Causal Agent of Heartwater

Ehrlichia ruminantium is an obligate intracellular bacterium that causes heartwater, a fatal tick-borne disease of livestock, with high economical impact in sub-Saharan Africa and some islands in the Indian Ocean and the Caribbean. In host endothelial cells, E. ruminantium has a complex life cycle with two forms: the extracellular and infectious elementary bodies and the intracellular, non-infectious but metabolically active reticulate bodies. Several control and prevention strategies against heartwater have been developed but with limited efficacy. Since 1990, the pace of heartwater research has accelerated rapidly due to important advances in diagnosis, epidemiology, phylogeny and immunology. The recent use of Omics approaches significantly contributed to identify E. ruminantium virulence factors and provide new insights on vector–pathogen–host interactions. This knowledge opens now a window of opportunity to develop improved vaccines against heartwater.