Chlamydia are a genus of successful obligate intracellular pathogens spread across humans, wildlife, and domesticated animals. The most common species reported in livestock in this genus are Chlamydia abortus, Chlamydia psittaci, Chlamydia suis, and Chlamydia pecorum. Chlamydial infections trigger a series of inflammatory disease-related sequelae including arthritis, conjunctivitis, pneumonia, and abortion. Other bacteria in the phylum Chlamydiae have also been reported in livestock and wildlife but their impact on animal health is less clear. Control of chlamydial infections relies on the use of macrolides, fluoroquinolones, and tetracyclines. Tetracycline resistance (TETR) reported for porcine C. suis strains in association with the use of tetracycline feed is a potentially significant concern given experimental evidence highlighting that the genetic elements inferring TETR may be horizontally transferred to other chlamydial species. As documented in human Chlamydia trachomatis infections, relapse of infections, bacterial shedding post-antibiotic treatment, and disease progression despite chlamydial clearance in animals have also been reported. The identification of novel chlamydiae as well as new animal hosts for previously described chlamydial pathogens should place a renewed emphasis on basic in vivo studies to demonstrate the efficacy of existing and new antimicrobial treatment regimes. Building on recent reviews of antimicrobials limited to C. trachomatis and C. suis, this review will explore the use of antimicrobials, the evidence and factors that influence the treatment failure of chlamydial infections in animals and the future directions in the control of these important veterinary pathogens.

BackgroundChlamydia pecorum is a globally significant livestock pathogen causing pathology and production losses. The on-farm infection and serological dynamics and the relevance of existing diagnostic tools for diagnosing C. pecorum in livestock remains poorly characterized. In this study, we characterized the antigen and antibody dynamics of this pathogen in a longitudinal study of prime lamb production, utilizing the infection focused C. pecorum-specific 16S rRNA qPCR assay and serology based chlamydial Complement fixation Test (CFT).MethodsThe study consisted of 76 Border Leicester mixed sex lambs (39 females and 37 males) that were sampled bimonthly from 2–10 months of age in a commercial farm operating in Central NSW, Australia. Blood/plasma was analysed for CFT antibodies, and swabs from conjunctival, rectal and vaginal sites were analysed for C. pecorum shedding using qPCR. We assessed the temporal and overall dynamics of C. pecorum in lambs, including detailed description and comparison of qPCR and CFT, the timing of first detection by either diagnostic method, the lag between infection and antibody response; and the distribution of qPCR load and CFT antibody titre over time.ResultsOver the study period, C. pecorum was highly prevalent (71.0% by qPCR, 92.1% by CFT, 96.0% by both), with 21.1% (16/76) lambs shedding ≥1, 000 qPCR copies/µl (denoted as high shedders). C. pecorum shedding (as evidence of infection) were first observed at two months of age (14.4%) with a significant peak of infection occurring at six months of age (34.2%), whereas seroconversions peaked at eight months of age (81.5%). 52.6% of C. pecorum qPCR and CFT positive lambs became qPCR negative by 10 months of age, indicating clearance of chlamydial infection. Although CFT is utilised for on-farm detection of active infection, we confirm that it lagged behind qPCR detection (average lag 1.7 ± 2.1 months) and that the proportion of qPCR positives simultaneously identified by CFT was low with 2/11 (18.1%), 0/13, 17/25 (68.0%), 5/7 (71.4%) and 1/10 (10.0%) concurrent seroconversions occurring at two, four, six, eight and 10 months of age, respectively.DiscussionThis work reveals rapid rates of C. pecorum infection and widespread exposure during lamb production. The comparison of molecular and serological diagnostic agreement longitudinally, supports the use of qPCR as an important ancillary tool for the detection of active infections in conjunction with chlamydial CFT for routine veterinary diagnostics. Development of rapid Point-of-Care (POC) tools for diagnosing active infection would be valuable for producers and veterinarians.

BackgroundArthritis is an economically significant disease in lambs and is usually the result of a bacterial infection. One of the known agents of this disease is Chlamydia pecorum, a globally recognised livestock pathogen associated with several diseases in sheep, cattle and other hosts. Relatively little published information is available on the clinical, diagnostic and pathologic features of C. pecorum arthritis in sheep, hindering efforts to enhance our understanding of this economically significant disease. In this case series, a combination of standard diagnostic testing used routinely by veterinarians, such as the Chlamydia complement fixation text (CFT), veterinary clinical examinations, and additional screening via C. pecorum specific qPCR was used to describe putative chlamydial infections in five sheep flocks with suspected ovine arthritis.Case presentationFive separate cases involving multiple lambs (aged six to ten months) of different breeds with suspected C. pecorum arthritis are presented. In two of the five cases, arthritic lambs exhibited marked depression and lethargy. Arthritis with concurrent conjunctivitis was present in four out of five lamb flocks examined. Chlamydia CFT demonstrated medium to high positive antibody titres in all flocks examined. C. pecorum shedding was evident at multiple sites including the conjunctiva, rectum and vagina, as determined via qPCR. Two of the five flocks received antimicrobials and all flocks recovered uneventfully regardless of treatment.ConclusionThis case series highlights the features a field veterinarian may encounter in cases of suspected ovine chlamydial arthritis. Our analysis suggests a presumptive diagnosis of chlamydial arthritis in lambs can be made when there is evidence of joint stiffness with or without synovial effusion and elevated chlamydia antibody titres. C. pecorum-specific qPCR was found to be a useful ancillary diagnostic tool, detecting Chlamydia positivity in low or negative CFT titre animals. Variables such as symptom duration relative to sampling, sheep breed and farm management practices were all factors recorded that paint a complex epidemiological and diagnostic picture for this disease. These case studies serve to provide a platform for further research to improve diagnostic testing and new treatment and control strategies for C. pecorum infections in sheep.

Summary Chlamydiae are globally widespread obligate intracellular bacteria, which several species are a well‐recognized threat to human and animal health. In Australia, the most successful chlamydial species are the infamous koala pathogen C. pecorum, and C. psittaci, an emerging pathogen associated with zoonotic events. Little is known about infections caused by other chlamydial organisms in Australian livestock or wildlife. Considering that these hosts can be encountered by humans at the animal/human interface, in this study, we investigated genetic diversity of chlamydial organisms infecting Australian domesticated and wild ungulates. A total of 185 samples from 129 domesticated (cattle, horses, sheep, and pigs) and 29 wild (deer) ungulate hosts were screened with C. pecorum and C. psittaci species‐specific assays, followed by a screen with pan‐Chlamydiales assay. Overall, chlamydial DNA was detected in 120/185 (65%) samples, including all ungulate hosts. Species‐specific assays further revealed that C. pecorum and C. psittaci DNA were detected in 27% (50/185) and 6% (11/185) of the samples, respectively, however from domesticated hosts only. A total of 46 “signature” 16S rRNA sequences were successfully resolved by sequencing and were used for phylogenetic analyses. Sequence analyses revealed that genetically diverse novel as well as traditional chlamydial organisms infect an expanded range of ungulate hosts in Australia. Detection of the C. psittaci and C. pecorum in livestock, and novel taxa infecting horses and deer raises questions about the genetic make‐up and pathogenic potential of these organisms, but also concerns about risks of spill‐over between livestock, humans, and native wildlife.

Chlamydia trachomatis is the primary cause of bacterial sexually transmitted infections worldwide, with a disturbing increase in annual rates. While there is a plethora of data on healthy and pathogenic vaginal microbiomes—defining microbial profiles and associations with sexually transmitted infections (STIs)—far fewer studies have similarly examined the endocervix or rectum.