| Summary: | <p>Abstract</p> <p>Background</p> <p>Prevention and control of ovine enzootic abortion (OEA) can be achieved by application of a live vaccine. In this study, five sheep flocks with different vaccination and infection status were serologically tested using a competitive enzyme-linked immunosorbent assay (cELISA) specific for <it>Chlamydophila (Cp.) abortus </it>over a two-year time period.</p> <p>Results</p> <p>Sheep in Flock A with recent OEA history had high antibody values after vaccination similar to Flock C with natural <it>Cp. abortus </it>infections. In contrast, OEA serology negative sheep (Flock E) showed individual animal-specific immunoreactions after vaccination. Antibody levels of vaccinated ewes in Flock B ranged from negative to positive two and three years after vaccination, respectively. Positive antibody values in the negative control Flock D (without OEA or vaccination) are probably due to asymptomatic intestinal infections with <it>Cp. abortus</it>. Excretion of the attenuated strain of <it>Cp. abortus </it>used in the live vaccine through the eye was not observed in vaccinated animals of Flock E.</p> <p>Conclusion</p> <p>The findings of our study indicate that, using serology, no distinction can be made between vaccinated and naturally infected sheep. As a result, confirmation of a negative OEA status in vaccinated animals by serology cannot be determined.</p>
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