Suspected clinical Lyme disease in horses: Serological and antigen testing differences between clinically ill and clinically normal horses from an endemic region

Equine Lyme disease is difficult to diagnose because of its nonspecific clinical signs and the high incidence of subclinical infection in endemic regions. In this study we compared serology, antigen presence, hematology, blood chemistries and clinical presentation of 22 horses from a highly endemic region that were clinically diagnosed with Lyme disease to that of 21 clinically normal horses from the same region. We found that horses clinically diagnosed with Lyme disease were more likely to have Borrelia burgdorferi spirochetal DNA in their blood and urine, have a higher percentage of positive immunoblots containing antibodies to certain B. burgdorferi proteins, and tend to have higher ELISA titers than healthy horses from the same region. These results may help to improve diagnostic testing for equine Lyme disease.