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Medical Index
First Posted Apr 27, 2010
Jul 25, 2010

Granulocytic Anaplasmosis/Anaplasma phagocytophila (Ehrlichia equi)in Horses

Anaplasma phagocytophila (E. equi) targets granulocytes not monocytes. It is transmitted by Ixodes spp. tick vectors. The two most common are Ixodes pacificus and Ixodes scapularis. Lyme disease is transmitted by the same two species. Granulocytic ehrlichiosis is most prevalent in late fall to spring. It is most prevalent in the state of California.


  • Fever
  • Edema such as stocking up
  • Ataxia (incoordination)
  • Lethargy
  • Anemia and lethargy

There are a number of other diseases in horses that present with much the same symptoms such as equine infectious anemia virus (EIAV), equine arteritis virus (EAV), Strangles (Streptoccus equi), and Potomac Fever.

Blood work is used along with Polymerase chain reaction (PCR) in the diagnosing of this disease. Once the determination has been made that, indeed, your horse has granulocytic anaplasmosis the treatment is to give oxytetracycline.

Medical Index