• Two species affect dogs, and both are transmitted by ticks or, rarely, through infected blood transfusions.
• Anaplasma phagocytophilum (formerly classified as an Ehrlichia species) is consistently found as a coinfection with Borrelia burgdorferi. Coinfection is more likely to result in clinical disease.
• Anaplasma platys is typically found incidentally when veterinarians are diagnosing thrombocytopenia.
• These parasites are not found on erythrocytes. Anaplasma phagocytophilum is found within the cytoplasm of neutrophils, and A. platys is seen only within platelets. Because of that, they are located largely within the read area of a smear.
• Anaplasma phagocytophilum is seen as a large morula within the cytoplasm (Figure 1). More than one morula may be present.
• Anaplasma platys appears as dark-staining granules within platelets (Figure 2).
1. Anaplasma phagocytophilum on a blood smear. Note the large morula in the cytoplasm (Wright’s stain; 100x).
2. Anaplasma platys on a blood smear. The small dark-purple dots throughout the smear are A. platys within platelets (Wright’s stain with Prussian blue; 40x).
• Thrombocytopenia is a typical clinical sign of an A. platys infection.
• Anaplasma phagocytophilum can be acute or subclinical. Frequent clinical signs include fever, lethargy, inappetence, lameness, stiffness, or a reluctance
to move. Mild splenomegaly and lymphadenomegaly can occur. Laboratory findings commonly consist of thrombocytopenia, lymphopenia,
eosinopenia, and a mild anemia.
• Therapy is the same for both species: oral administration of doxycycline (5 to 10 mg/kg once or twice daily for 28 days).
• Corticosteroid administration is not recommended.