Influence of Chlamydia suis on reproductive outcome in farms with and without tetracycline treatment of sows.

Porcine genital chlamydiosis is considered a potential cause of reproductive failure, with Chlamydia (C.) suis being the most prevalent chlamydial species. To assess its pathogenic relevance, 50 Austrian piglet-producing farms were investigated: 40 farms with reproductive disorders (20 with tetracycline-treatment (tet), 20 without (no-tet)) and 10 clinically unaffected control farms. Samples from 770 sows (tet: n = 333, no-tet: n = 337, control: n =100) including blood, cervical and rectal swabs, dust samples and one pooled nursery fecal sample per farm were analyzed. Thirty-seven reproductive-tracts and six abortion cases were examined. Species-specific real-time PCR detected cervical C. suis shedding in 2.1% of sows (tet: n =5, no-tet: n = 10, control: n = 1). Rectal shedding was found on 45 farms and in 39.7% of sows overall (tet: n = 37.8%, no-tet: n = 39.2%, control: n = 48%). C. pecorum DNA was identified in one cervical and seven rectal swabs. Chlamydiaceae-specific antibodies were detected by complement fixation test on all farms and in 49.8% of sows overall, without association between study group and shedding or serological status. C. suis DNA was detected in 28% of dust and 96% of nursery fecal samples, whereas reproductive tract and abortion material were largely PCR-negative. Analyzing 42 C. suis isolates high rates of tetracycline resistance were found in all study groups via tetA(C) PCR (tet: n = 93.75%, no-tet: n = 78.3%, control: n = 100%) and in vitro susceptibility testing (tet: n = 75%, no-tet: n = 60.8%, control: n = 100%). Parity had negative effects on clinical signs, rectal shedding and antibody expression. C. suis appears to play a limited role in reproductive failure, while routine tetracycline treatment should be critically reconsidered due to frequent resistance.