The clinical importance of Anaplasma spp. infection remains unclear in sick and healthy dogs. Coinfections may play a role in expression of illness. The purpose of this retrospective study was to compare seroprevalence in hospital clinic (HC) dogs and healthy large breed blood donor (BD) dogs, and to review clinicopathologic findings in exposed sick dogs. Medical records were reviewed for variables such as signalment, lameness, fever, results of CBC, biochemical profile, urinalysis, and serologic test results for antibodies to other tick-borne diseases.
Between Nov 2006 and Dec 2007, the SNAP-4Dx (IDEXX) in-house test was used to determine presence of heartworm antigen and antibodies against Borrelia burgdorferi (Bb), Ehrlichia canis, and Anaplasma phagocytophilum/platys (Ap). From Dec 1999 through Oct 2006, anti-Ap antibodies were tested by IFA assay (ProtaTek Laboratories, AZ).
Positive Ap antibody test results were found in 17/267 (6.4%) BD dogs (mean 4.5 yrs old) compared with 54/956 (5.6%) of HC dogs (mean 6.4 yrs old) during the period of Nov 2006-Dec 2007. In addition, 4 seronegative infected HC cases had neutrophilic morulae in blood smears, joint tap, or spinal fluid cytologic examination (total HC Ap cases = 58/960 or 6.0 %). During this period of time 65/345 (18.8%) BD and 180/1029 (17.5%) HC dogs were Lyme-positive. Among the Ap-seropositive dogs, anti-Bb antibodies were also found in 23/58 (39.7%) HC dogs and 8/17 (47.1%) healthy BD dogs.
Medical records of 70 Ap-seropositive or infected HC dogs from Dec 1999-Dec 2007 were studied. According to the owners, 19/70 (24.3%) dogs were not on topical ectoparasite prevention. Owners reported lameness in 22/70 (31.4%), lethargy in 18/70 (25.7%), and anorexia in 7/70 (10%) dogs. Common physical exam findings included fever > 103F in 27/70 (38.6%), lameness in 23/70 (32.8%) dogs, and neurologic abnormalities in 10/70 (14.3%) dogs. Common laboratory abnormalities included thrombocytopenia (< 177 x103/ul) in 30/70 (42.3%) dogs, anemia (HCT < 39.9%) in 35/70 (50%) dogs, and urine protein/creatinine ratio > 0.5 in 10/20 (50%) dogs. Antibodies to Bb were found in 32/70 (45.7%) dogs and 8/13 dogs were positive for Bartonella spp. antibodies.
Since sampling of a variety of sick dogs was not routinely done and was biased toward cases with clinical signs suspicious for tick-borne disease, e.g., fever, lameness, cytopenias, and/or proteinuria, a case-controlled study is ongoing, to compare the clinicopathologic findings in contiguous seronegative cases done in the same laboratory before and after each seropositive case.
In conclusion, clinically ill dogs were not found to be more likely seropositive for Ap antibodies than were healthy blood donor dogs. Confusion regarding cause and effect of Ap exposure and illness may be confounded by sampling bias and co-infections, especially with Lyme disease.