Ehrlichia species, probable emerging human pathogens in sub-Saharan Africa: environmental exacerbation.

Ehrlichiae are obligate intracellular Gram-negative tick-borne bacteria that are responsible for life-threatening emerging human zoonoses and diseases of veterinary importance worldwide, collectively called ehrlichioses. The genus Ehrlichia consists of five recognized species, including E. canis, E. chaffeensis, E. ewingii, E. muris, and E. ruminantium. The recent discoveries of Ehrlichia species in new areas and of tick species that were previously thought to be uninfected by these agents have suggested that these agents may have wider distribution than originally thought. Environmental factors like temperature, migration, control failure, and host population have been known to exacerbate the spread of Ehrlichia species. Human cases of moderate to severe disease caused by E. chaffeensis have been reported mainly in North America. In this article, we present an overview of ehrlichiae as emerging pathogens in sub-Saharan Africa, where E. ruminantium, the causative agent of heartwater, a disease of domestic and wild ruminants, is most established. Molecular evidence indicates that E. ruminantium may be an emerging pathogen of a life-threatening human disease. Ehrlichia ruminantium is considered an agricultural biothreat, with several strains reported throughout sub-Saharan Africa, where the infection is considered endemic. Understanding the diversity of E. ruminantium and other Ehrlichia species from all geographically distinct areas of sub-Saharan Africa may enhance our knowledge of the pathogenesis and epidemiology of these pathogens.