Anaplasma ovis is an arthropod-borne rickettsial pathogen that induces acute anemia in sheep and goats following invasion and replication within erythrocytes. Although A. ovis does not infect cattle, this pathogen has been reported to infect wild ruminants. A. ovis is transmitted by Rhipicephalus bursa, Haemaphysali sulcata and probably other ticks in the old world and by Dermacentor andersoni in the Americas. Reservoirs of this pathogen naturally occur in mammalian or other tick hosts with persistent infection. Acute anaplasmosis in goats is characterized by depression, debility, marked decline in body weight, fever, progressive anemia, and reduced milk production.