Borrelia burgdorferi infection is common in horses living in Lyme endemic areas and the geographic range for exposure is increasing. Morbidity after B. burgdorferi infection in horses is unknown. Documented, naturally occurring syndromes attributed to B. burgdorferi infection in horses include neuroborreliosis, uveitis, and cutaneous pseudolymphoma. Although other clinical signs such as lameness and stiffness are reported in horses, these are often not well documented. Diagnosis of Lyme disease is based on exposure to B. burgdorferi, cytology or histopathology of infected fluid or tissue and antigen detection. Treatment of Lyme disease in horses is similar to treatment of humans or small animals but treatment success might not be the same because of species differences in antimicrobial bioavailability and duration of infection before initiation of treatment. There are no approved equine label Lyme vaccines but there is strong evidence that proper vaccination could prevent infection in horses.
Lyme neuroborreliosis-characterized as chronic, necrosuppurative to nonsuppurative, perivascular to diffuse meningoradiculoneuritis-was diagnosed in 2 horses with progressive neurologic disease. In 1 horse, Borrelia burgdorferi sensu stricto was identified by polymerase chain reaction amplification of B burgdorferi sensu stricto-specific gene targets (ospA, ospC, flaB, dbpA, arp). Highest spirochetal burdens were in tissues with inflammation, including spinal cord, muscle, and joint capsule. Sequence analysis of ospA, ospC, and flaB revealed 99.9% sequence identity to the respective genes in B burgdorferi strain 297, an isolate from a human case of neuroborreliosis. In both horses, spirochetes were visualized in affected tissues with Steiner silver impregnation and by immunohistochemistry, predominantly within the dense collagenous tissue of the dura mater and leptomeninges.
PASSIVE TRANSFQR of colostral immunoglobulin (Ig) G from mare to foal is important for the protection of the equine neonate from infectious disease.'-9 Serum IgG concentration is an indicator of the success of passive tran~fer.~." Early determination of a foal's passive transfer status (serum IgG concentration) is necessary for prophylactic management of the foal with inadequate IgG.331 I Timely identification of these foals requires an accurate test with rapidly available results. Tests that have been used for evaluating passive transfer include zinc sulfate precipitation, latex agglutination, and radial immunodiffusionThe zinc sulfate precipitation test is a semiquantitative assay of the globulin fraction in serum samples, but results may vary with the operator, degree of hemolysis present in the sample, field conditions, and reagent q~a1ity.I~ Latex agglutination test kits provide rapid results. Presently, however, these kits are prepared with an upper limit of 400 mg/dl or more, rather than 800 mg/dl or more of IgG. The RID is the standard quantitative assay for From the Departments of Veterinary Clinical Sciences (Bertone, Curtis) and the
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