Serologic Diagnosis of Equine Borreliosis: Evaluation of an In-Clinic Enzyme-Linked Immunosorbent Assay (SNAP® 4Dx®)

SNAP® 4Dx® (IDEXX Laboratories, Westbrook, ME) is a commercially available in-office test kit for the simultaneous detection of Dirofilaria immitis antigen and antibodies to Borrelia burgdorferi, Anaplasma phagocytophilum, and Ehrlichia canis in blood, plasma, or serum of dogs. The test kit is an enzyme-linked immunosorbent assay that uses the synthetic peptide C6 derived from the IR6 region within the Borrelia membrane protein VlsE, peptides derived from the immunodominant p44 protein of A phagocytophilum, and the p30 and p30-1 protein of E canis. Studies with canine samples suggest that SNAP® 4Dx® is particularly useful in endemic areas because it can be conveniently and reliably used in the clinic to determine the infection status of a dog. We evaluated the performance of SNAP® 4Dx® for the detection of antibodies to Lyme and Anaplasma in equine serum samples from Northeastern United States and Alaska. A total of 164 equine samples obtained from the University of Connecticut were tested by SNAP® 4Dx®, Lyme disease immunofluorescence assay (IFA; VMRD, Inc., Pullman, WA) and QualiCodeTM B burgdorferi IgG/IgM Western Blot Kits (Immunetics, Cambridge, MA). For A phagocytophilum, an IFA was utilized. Of the serum samples tested, 109 were positive for Lyme and 54 samples were positive for A phagocytophilum by SNAP® 4Dx®. Twenty-four samples were co-infected with Lyme and A phagocytophilum. Of the 109 samples that tested positive for Lyme by SNAP® 4Dx®, 106 were positive by the Lyme Western blot assay. The 3 discordant samples were positive by IFA and had a low reciprocal antibody titer of 64. All 54 samples that were positive for A phagocytophilum by SNAP® 4Dx® tested positive by IFA. Each of the SNAP® 4Dx®-negative samples was negative by Western blot and IFA. Thus, relative to Lyme Western Blot assay, SNAP® 4Dx® had a sensitivity and specificity of 100% and 95%, respectively, for the detection of antibodies to Lyme. Relative to IFA, SNAP® 4Dx® had a sensitivity and specificity of 100% for the detection of antibodies to A phagocytophilum. These results indicate that SNAP® 4Dx® can be successfully used to detect antibodies to B burgdorferi and A phagocytophilum in infected horses. Serologic Diagnosis of Equine Borreliosis: Evaluation of an In-Clinic Enzyme-Linked Immunosorbent Assay (SNAP® 4Dx®) Ramaswamy Chandrashekar, MS, PhD1 Daryn Daniluk, BS1 Scott Moffitt, DVM1 Leif Lorentzen, DVM1 Jeff Williams, DVM2 1IDEXX Laboratories Westbrook, Maine, USA 2Rhinebeck Equine LLC Rhinebeck, New York, USA