SEROLOGICAL TITERS OF EQUINE MONOCYTIC EHRLICHIOSIS ASSOCIATED WITH GASTROINTESTINAL DISORDERS AND SEROLOGICAL FOLLOW-UP ON 2 ENDEMIC FARMS

The purpose of this work was to study the association of positive sero logical titers to Ehrlichia risticii, the causative agent of equine mo nocytic ehrlichiosis (EME) with gastro-intestinal disorders in hospita lized horses referred to The Ohio State University College of Veterina ry Medicine Teaching Hospital (OSU VMTH). In addition, serological tit ers for E. risticii were monitored in two horse populations with endem ic EME for one season to monitor temporal changes in titers. A statist ically significant difference was found between the proportion of the total hospitalized horse population presented with a gastro-intestinal disorder during the study period, and study horses with IFA titers gr eater-than-or-equal-to 1:80 with these signs (P < 0.05). No such diffe rence was found between the proportion of the total hospital horse pop ulation presented with signs of gastro-intestinal disorder, and the st udy horses with IFA titers of 1:20-1:40 with these signs, suggesting t hat these titers may not have any clinical significance for EME (P > 0 .05) Thirty-eight horses on two farms endemic for EME were tested appr oximately every 3 weeks, 33 of which were tested serially at least two times. Five of the 38 horses (13.2%) had IFA titers greater-than-or-e qual-to 1:80 - two that were positive initially and three that serocon verted during the study; 15 horses' titers fluctuated between negative (IFA titers < 1:20) and exposed titers (1:20 through 1:40); and 18 ho rses remained negative throughout the study.