Anaplasmosis in a dog on Vancouver Island.

In February of 2015, a 7-year-old, 33 kg, spayed female Labrador retriever dog was presented to our hospital with a 1-day duration of decreased appetite, lethargy, and a stiff and stilted gate. She had vomited once the previous day and the owners mentioned that she may have ingested something from the garbage. This dog also had a history of acquiring several ticks within the previous 2 wk and that 2 ticks had been removed by the owners just prior to her examination. The Pacific deer tick, Ixodes pacificus, is commonly encountered on dogs in this area of Vancouver Island in 2 seasonal periods; a winter (January–February) spike and then throughout the summer (June through September). This dog had no history of travel off Vancouver Island. On distant examination, this dog had an obvious right hind leg lameness with a shifting of weight from this limb while walking. There were no obvious neurological deficits. Her temperature was 40.3°C, her heart rate was 170 beats/min, and her respiratory rate was normal. Her mucous membranes were pink and mildly tacky. There was no discernible pain or abnormalities on abdominal palpation. An orthopedic examination revealed no obvious pain response on flexion or extension of any limbs, nor any obvious swelling of any joints. Abdominal radiographs were taken and in-house complete blood (cell) count (CBC) and serum chemistry were performed. The radiographs revealed spondylosis of several lumbar vertebrae but no other skeletal or soft tissue abnormalities were detected. The chemistry panel was unremarkable with all parameters within normal range. The CBC, however, revealed severe thrombocytopenia [18 × 109/L, reference interval (RI): 148 to 484 × 109/L] and the blood smear showed no platelet clumping to skew this finding. There was a leukopenia (3.6 × 109/L, RI: 5.05 to 16.76 ×109/L) with a notable lymphopenia (0.24 × 109/L, RI: 1.05 to 5.19 × 109/L), an absolute eosinopenia, and a normal neutrophil count (3.5 × 109/L, RI: 2.95 to 11.64 × 109/L). The red cell count was normal (7.0 × 1012/L, RI: 5.65 to 8.87 ± 109/L). Upon examination of the blood smear, it was readily apparent that there were cytoplasmic inclusion bodies (morulae, Figure 1) present in the neutrophils (seen in 27 out of 100 neutrophils counted). Figure 1 Blood smear showing morulae (cluster of bacteria) in a neutrophil. A tentative diagnosis of anaplasmosis was made based on the history, clinical signs, and findings on the blood smear (1,2). Treatment included doxycycline 300 mg, q12h for 14 d and prednisone 12.5 mg, q12h for 5 d, then q24h for 7 d. Serum was sent to Idexx Laboratory for a 4Dx SNAP test which is an enzyme-linked immunosorbent assay (ELISA) screening test for the presence of circulating antibodies to Anaplasma phagocytophilum, A. platys, Ehrlichia canis, and E. ewingii, Borrellia burgdorferi, and Dirofilaria antigen. The results were negative for all organisms. Upon consultation with the reference laboratory, a real-time polymerase chain reaction (PCR) test for Anaplasma spp. DNA was performed on the same serum sample. This test was positive for Anaplasma DNA, thus confirming the tentative diagnosis. The patient improved significantly after a few days of therapy and had an uneventful recovery. This case is similar in many respects to a previously documented case of anaplasmosis in a dog on Vancouver Island (3). Clinicians are reminded that screening tests for antibodies may prove negative when animals present in the acute phase of anaplasmosis which may last 7 to 14 d (2,4) and that laboratory confirmation for the presence of DNA may be required to confirm presence of the organism. There are several reports of dogs that were positive by PCR but negative in tests for antibody to Anaplasma, including a recent report on 3 dogs from Saskatoon (5). In addition, there is a general sense that in many areas of North America, including southern Vancouver Island, ticks are more prevalent and the incidence of tick bites in dogs appears to be increasing. Veterinarians are advised to be vigilant in testing for tick-borne diseases in dogs with a history of illness following tick exposure. Veterinary technicians viewing smears in-house need to be aware that the presence of inclusion bodies in neutrophils is a significant clue in the diagnosis of anaplasmosis.

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