Serologic confirmation of Ehrlichia equi and Borrelia burgdorferi infections in horses from the northeastern United States

Objective-To determine whether horses living in tick-infested areas of nort heastern United Stales with clinical signs of borreliosis or granulocytic e hrlichiosis had detectable serum antibodies to both Borrelia burgdorferi an d Ehrlichia equi. Design-Prospective study. Animals-Serum samples from 51 clinically normal horses, 14 horses with clin ical signs of borreliosis, and 17 horses with clinical signs of granulocyti c ehrlichiosis. Procedure-Serum B burgdorferi or E equi antibodies were measured by use of an ELISA, immunoblot analysis, or indirect fluorescent antibody (IFA) stain ing. Results-Of the 82 serum samples tested, 37 (45.1%) and 13 (15.9%) had detec table antibodies to B burgdorferi or E equi, respectively. Test results ind icated that 12 horses had been exposed to both agents, 11 of these horses h ad granulocytic ehrlichiosis. The ELISA regularly detected antibodies to th e following recombinant protein (p) antigens of B burgdorferi: p29, p37, p3 9, and p41-G. The use of immunoblot analysis confirmed ELISA results by ind icating antibody reactivities to antigens of whole-cell B burgdorferi havin g molecular masses of predominantly 31, 34, 37, 39, 41, 58, and 93 kd. Conclusions and Clinical Relevance-Horses living in areas where ticks (Ixod es scapularis) abound are sometimes exposed to multiple pathogens. Analyses for specific recombinant borrelial antibodies using an ELISA can help sepa rate horses with borreliosis from those with granulocytic ehrlichiosis, eve n when antibodies to both etiologic agents are detected in serum samples. A nalysis using immunoblots is sensitive, and along with ELISA or IFA procedu res, is suitable for confirming a clinical diagnosis of each disease.