Clinical Pathology Case Study: Anaplasmosis in a dog

Cytologic description and interpretation

Thrombocytopenia is confirmed with only 4-5 platelets per 100x field.  In addition, several neutrophils contain aggregates of basophilic cocci bacteria, consistent with Anaplasma or Ehrlichia morula.

Interpretation: Based on the dog’s geographic location and travel history, Anaplasma phagocytophilum is the presumed organism.

Discussion

Anaplasmosis (typically Anaplasma phagocytophilum) is a tick-borne infection found worldwide in a variety of animals. Most infections are asymptomatic or cause short-lived, mild clinical signs (eg. anorexia, lethargy, stiffness, fever). Thrombocytopenia is the most common laboratory abnormality. The thrombocytopenia is typically mild and is not associated with bleeding abnormalities.

In dogs, Anaplasmosis has a similar presentation to other tick-borne diseases, including Lyme disease and Ehrlichiosis. Anaplasma and Ehrlichia organisms can occasionally be seen within leukocytes of acutely-infected animals. If found, the organism and patient’s geographic location can be used to reach a definitive diagnosis. However, visible organisms are only present in acute infections and sometimes in very low numbers. Therefore, PCR testing, which is more sensitive than blood smear evaluation, is another diagnostic option.

In areas where Anaplasmosis is common, many dogs are exposed subclinically to A. phagocytophilum and develop antibodies that can persist for 6 months after infection.  A positive antibody test therefore should always be interpreted in combination with the patient’s clinical signs.