Eperythrozoon ovis infection in a commercial flock of sheep

A flock of sheep consisting of 60-70 winterfed ewes was examined. Blood was collected from approximately 30% of the sheep four times from 1991 to 1995. Eperythrozoon ovis (Ep. ovis) organisms were not detected in blood smears stained with Wright's stain in 1991 and 1993. In 1995, examination of blood smears stained with acridine orange revealed Ep. ovis organisms in 11 of 26 sheep, whereas examination of smears stained with Wright's stain revealed organisms in only one ewe with a high degree of infection. The prevalence of antibodies detected by IFAT varied from 58-100%. The antibody titres varied from 1:20 to 1:12,000. This investigation indicates that Ep. ovis infection once present in a flock of sheep may spread easily among the sheep, and that the infection seems to persist within the flock.