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Category: Dogs

Efficacy of Doxycycline Therapy for Anaplasma Phagocytophilum Infection in Dogs
July 16, 2008 (published)
Pedro Diniz

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Preliminary results can be found here.

Study Start Date: 07/01/2008
Study End Date: 12/30/2009

Efficacy of doxycycline therapy for Anaplasma phagocytophilum infection in dogs

A. phagocytophilum is a tick-transmitted bacterium capable of infecting dogs, cats, horses, human beings and other species and causes Granulocytic Anaplasmosis. Clinical observations of selected cases; as well as preliminary data from an experimental study; have suggested that doxycycline may not clear the infection of A. phagocytophilum in all treated dogs. Since differences in antibiotic susceptibility can occur between experimental strains and wild strains of this organism; this study will evaluate the efficacy of doxycycline treatment for canine granulocytic anaplasmosis (CGA) and identify potential chronic A. phagocytophilum infections. Over a 2-month period; dogs presented with signs compatible with CGA that will be treated with doxycycline will be tested monthly using molecular techniques and serology at three time points: at the initial consultation; after doxycycline treatment (30 days) and after 60 days of the initial consultation. The study will evaluate not only the presence of the bacterium after treatment; but also clinical improvement of patients; based upon questionnaires for clients and clinicians. The study hopes to confirm the efficacy of the therapy for acute infection with A. phagocytophilum in naturally infected dogs.

Study Design:
Prospective, uncontrolled, repeated measures

Sample Size:

Inclusion Criteria:
Veterinarians from endemic areas for Anaplasma phagocytophilum in the US (Northeast, Upper Midwest and California) who anticipate diagnosing at least 5 dogs with CGA (canine granulocytic anaplasmosis) during the study period. Veterinarians must contact investigators before enrolling any patient and submitting samples, to receive the start-up package. Veterinarians should carefully review the study protocol, as they will be required to diligently complete all phases of the study with enrolled patients.

Enrolled dogs should present at least three of the following clinical signs or laboratory abnormalities:

  • Presence of ticks or history of tick infestation within 4 weeks,
  • Acute onset of lethargy or depression, fever (temperature > 102.9F), joint pain, neck pain, bleeding, anorexia, vomiting, neurological signs, inflammatory ocular disease, lameness, anemia, leukopenia, thrombocytopenia, or hyperproteinemia.

Exclusion Criteria:

  • Dogs treated with antibiotics or anti-rickettsial drugs during the 4 week period before this evaluation.
  • Dogs which will not be treated with doxycycline; or will be treated with an antibiotic other than doxycycline; or will be treated with doxycycline for a period of less than 28 days.
  • Dogs whose owners cannot return for follow-up examinations at 30 and 60 days after the initial evaluation.
  • Dogs whose owners do not agree or are not capable of applying the provided tick/flea preventive every 2 weeks.

Study Controls:

Study Endpoints:

Files for Download:
A more complete description of the study protocol can be found in this PDF file: AP protocol.pdf

Other Information:
Only PCR results will be provided to participating veterinarians during this study, since other tests will be performed in batches. PCR results will allow veterinarians to best direct patient therapy. PCR result from the initial sample (day 0) will be available within 4 weeks of submission (currently, the turnover is less than 1 week). Result from the second sample (day 30) will be provided only after the third sample (day 60) is received in our laboratory. Results will be provided by email, preferentially. Dogs with a negative PCR result will be expected to remain in the study and submit the remaining samples, although therapy may be altered after discussion with the PI.

Blood-EDTA (3 ml), serum (3 ml) and lymph node aspirates from day 0 and day 60.


  • Free PCR testing of blood samples for A. phagocytophilum (results available according specific schedule. Consult study protocol file)
  • Free complete blood cell counts (CBC).
  • Free tick preventive to be applied biweekly for 2 months. Veterinarians should contact investigators prior to sample submission to coordinate tick-preventive products for enrolled dogs.
  • Free shipping of samples.

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Full Disclosure information:

  • The study is funded by a grant from IDEXX Laboratories and Bayer Animal Health.
  • The investigator has declared that he has lectured on this topic with company sponsorship, and IDEXX laboratories support Dr. Diniz's salary and travel expenses related to presentations in scientific meetings. Bayer Animal Health provides tick preventive products for this study, only.
  • The study will be published if results are negative.
  • The study will be reported on VIN.
  • The authors will acknowledge VIN if the study is published.

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