Clinical and Laboratory Effects of Doxycycline and Prednisolone in Ixodes scapularis-Exposed Dogs With Chronic Anaplasma phagocytophilum Infection.

Persistent infection of Anaplasma phagocytophilum (AP) after treatment and immunosuppression has not been studied in dogs infected with AP after Ixodes scapularis infestation. This descriptive pilot study evaluated 6 laboratory-reared beagles that were persistently positive for AP antibodies after infestation with wild-caught I. scapularis. After 20 weeks, 3 of 6 dogs were administered doxycycline orally for 28 days, and all 6 dogs were then administered prednisolone at 2.2 mg/kg orally for 14 days. Blood was collected from all 6 dogs and evaluated by complete blood count, AP antibodies, and AP DNA at the beginning of the study and on Week 24 through Week 28. Blood was collected from 5 of the dogs on Week 48. No dogs developed recognizable clinical signs of illness or clinically relevant complete blood count abnormalities. During Week 26 through Week 28, all 6 dogs were negative for AP DNA. On Week 48, the 2 doxycycline treated dogs available for testing were negative for AP DNA and antibodies; the 3 untreated dogs were negative for AP DNA but positive for AP antibodies. In this model, the prednisolone protocol used did not activate AP in dogs with chronic, vector-induced infection. Since PCR evidence of AP infection resolved in both groups of dogs, the effect doxycycline had in eliminating AP infection from I. scapularis-exposed dogs will require further study.