Longitudinal study ofChlamydia pecorumin a healthy Swiss cattle population

Abstract

AbstractChlamydia pecorumis a globally endemic livestock pathogen but prevalence data from Switzerland has so far been limited. The present longitudinal study aimed to get an insight into theC. pecorumprevalence in Swiss cattle and investigated infection dynamics. The study population consisted of a bovine herd (n = 308) located on a farm in the north-eastern part of Switzerland. The herd comprised dairy cows, beef cattle and calves all sampled up to five times over a one-year period. At each sampling timepoint, rectal and conjunctival swabs were collected resulting in 782 samples per localization (total n = 1564).Chlamydiaceaescreening was performed initially, followed byC. pecorum-specific real-time qPCR on all samples. ForC. pecorum-positive samples, bacterial loads were determined. During this study,C. pecorumwas the only chlamydial species found. Animal prevalences included 5.2%-11.4%, 38.1%-61.5% and 55%-100% in dairy cows, beef cattle and calves, respectively. In all categories, the number ofC. pecorum-positive samples was higher in conjunctival (n = 151) compared to rectal samples (n = 65), however, the average rectal load was higher. At a younger age, the chlamydial prevalence and the mean bacterial loads were significantly higher. Of all sampled bovines, only 9.4% (29/308) were high shedders (number of copies per µl >1000). Calves, which tested positive multiple times, either failed to eliminate the pathogen between sampling timepoints or were reinfected, whereas dairy cows were mostly only positive at one timepoint. In conclusion,C. pecorumwas found in healthy Swiss cattle. Our observations suggested that infection takes place at an early age and immunity might develop over time. Although the gastrointestinal tract is supposed to be the main infection site,C. pecorumwas not present in rectal samples from dairy cows.