Abstract
BackgroundPrevention 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 Chlamydophila (Cp.) abortus over a two-year time period.ResultsSheep in Flock A with recent OEA history had high antibody values after vaccination similar to Flock C with natural Cp. abortus 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 Cp. abortus. Excretion of the attenuated strain of Cp. abortus used in the live vaccine through the eye was not observed in vaccinated animals of Flock E.ConclusionThe 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.
Highlights
Prevention and control of ovine enzootic abortion (OEA) can be achieved by application of a live vaccine
The aim of this study is to investigate a larger number of sheep over a two-year period in the field to compare flocklevel ELISA responses between (a) vaccinated, (b) naturally infected and (c) non-infected sheep flocks
All ewes (n = 15) of Flock A were serologically positive after vaccination showing a high median antibody value of 91.7%
Summary
Prevention and control of ovine enzootic abortion (OEA) can be achieved by application of a live vaccine. Five sheep flocks with different vaccination and infection status were serologically tested using a competitive enzyme-linked immunosorbent assay (cELISA) specific for Chlamydophila (Cp.) abortus over a two-year time period. Cp. abortus is generally introduced into immunologically naïve flocks by a latently infected animal with the agent being subsequently transmitted from aborting ewes via shedding of large amounts of infectious Chlamydia in the foetal membranes and in vaginal discharges [3]. Up to 30% of ewes may abort in the last trimester of gestation or give birth to weak or dead lambs. 5–10%) with sheep either born into the flock or newly introduced animals likely to suffer abortions during their initial pregnancies [4,5] Subsequent yearly losses in endemically infected flocks may decrease to a lower level (eg. 5–10%) with sheep either born into the flock or newly introduced animals likely to suffer abortions during their initial pregnancies [4,5]
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