Ehrlichia ruminantium is the causative agent of heartwater, an important tick-borne disease of livestock in Africa and the Caribbean that threatens the American mainland. The genome sequences of three strains of E. ruminantium have recently been published, revealing the presence of specific features related to genomic plasticity. E. ruminantium strains have traces of active genomic modifications, such as high substitution rates, truncated genes and the presence of pseudogenes and many tandem repeats. The most specific feature is the presence in all Ehrlichia of independent long-period tandem repeats, which are associated with expansion or contraction of intergenic regions.