• Open Access

Clinical Features of Canine Granulocytic Anaplasmosis in 18 Naturally Infected Dogs


  • Parts of this paper were presented as a poster at the 2007 ACVIM Congress in Seattle, USA (title: “Clinical features of 15 dogs naturally infected with Anaplasma phagocytophilum”) and at the 2007 DVG Congress in Berlin, Germany (title: “Canine granulozytäre Anaplasmose bei 16 natürlich infizierten Hunden”).

Corresponding author: Prof. Dr Barbara Kohn, Clinic for Small Animals, Faculty of Veterinary Medicine, Free University of Berlin, Oertzenweg 19b, D-14163 Berlin, Germany; e-mail: kohn@vetmed.fu-berlin.de.


Background: Anaplasma phagocytophilum, the causative agent of canine granulocytic anaplasmosis (CGA), is a Gram-negative intracellular organism transmitted by ixodid ticks. Thus far, only a few clinical studies evaluating dogs with CGA have been published.

Objectives: Evaluation of dogs naturally infected with A. phagocytophilum in which known co-infections were excluded.

Animals: Eighteen dogs with CGA.

Methods: Prospective study. The diagnosis of CGA was based on a positive PCR test result; dogs with co-infections were excluded. History, clinical findings, CBC, clinical biochemistry, infectious disease screening, diagnostic imaging, and the course of disease were evaluated.

Results: CGA was diagnosed based on a positive PCR test for A. phagocytophilum; 10 dogs also had morulae in neutrophils. Six of 18 dogs were seronegative to A. phagocytophilum, the others were seropositive. All dogs were acutely ill. The most common clinical findings were lethargy, inappetence, fever, and splenomegaly. Abnormal laboratory results included thrombocytopenia, anemia, lymphopenia, hypoalbuminemia, and abnormally high plasma alkaline phosphatase activity. In 6 of 10 dogs tested, the platelet-bound antibody test was positive; Coombs' test was negative in 9 dogs. All dogs were treated with doxycycline and recovered. PCR testing as well as blood smear analysis for morulae were negative in 14 tested dogs 2–8 weeks after beginning treatment.

Conclusions and Clinical Importance: Clinical findings in dogs with CGA were nonspecific. Positive platelet-bound antibody test results suggest immune-mediated platelet destruction as an important pathogenic mechanism. With correct diagnosis and treatment, prognosis is good.