LAUSR

OBJECTIVE To determine the prevalence of Anaplasma phagocytophilum and Borrelia burgdorferi infections in Pennsylvania horses. ANIMALS 271 horses. PROCEDURES A survey was conducted with PCR and serology to evaluate anaplasmosis and Lyme disease infections in horses from Pennsylvania that were suspected for tick-borne infection. RESULTS A phagocytophilum was detected in 19/271 (7.0%) Pennsylvania horses tested by the duplex PCR. B burgdorferi was not detected in any horse blood tested by PCR. Overall, 120/271 (44.3%) horses tested positive for presence of A phagocytophilum antibodies by at least the IDEXX SNAP 4Dx Plus lateral flow immunosorbent (SNAP) or indirect fluorescent antibody (IFA) assay, with 69 (25.5%) testing positive by both SNAP and IFA; 43 (15.9%) tested positive by IFA only, and 8 (3.0%) tested positive by SNAP only. Similarly, 209/271 (77.1%) horses tested positive for the presence of B burgdorferi antibodies by at least 1 test, with 139 (51.3%) testing positive by both SNAP and IFA; 45 (16.6%) tested positive by SNAP only, and 25 (9.2%) tested positive by IFA. CLINICAL RELEVANCE Both A phagocytophilum and B burgdorferi are important tick-borne infections. The study provides prevalence data for both A phagocytophilum and B burgdorferi and compares test performance. For serologic detection, IFA detected antibodies to A phagocytophilum in a higher proportion (41.3%) of horses compared to SNAP (28.4%), while SNAP detected antibodies to B burgdorferi in a higher proportion (67.9%) of horses compared to IFA (60.5%). Both diseases showed a high seroprevalence in all areas surveyed.