ABSTRACT
The presently constituted tribe Ehrlichieae contains three genera: Cowdria, Ehrlichia, and Neorickettsia. Cowdria and Ehrlichia are tick-transmitted and cause disease in domestic animals. The Ehrlichiae are parasites of domestic animals, and apparently are indigenous to the Mediterranean Basin and Europe. Classification of parasites on the basis of their tissue tropisms, although artificial, may be useful temporarily until the relationships between the various species become better known. The life cycles still need to be elucidated for most, and almost nothing is known of their evolutionary relationships. The whole question of the Ehrlichia-like agents of domestic animals is probably much more complex than it appears and needs careful and intensive study. Classification of parasites on the basis of their tissue tropisms, although artificial, may be useful temporarily until the relationships between the various species become better known. The life cycles still need to be elucidated for most, and almost nothing is known of their evolutionary relationships.
