Chlamydia pecorum (C. pecorum), an obligate intracellular bacterial pathogen, commonly isolated from the gastrointestinal tract, is ubiquitous in livestock globally. In sheep, C. pecorum is mainly associated with keratoconjunctivitis and polyarthritis. However, it has also been implicated in respiratory disease1, abortions2 and enteritis3. Faecal shedding has been documented in clinically healthy4,5 and diseased sheep6. The major route of transmission is believed to be faecal-oral7.
Research is still needed to understand the true impacts of this pathogen in sheep with subclinical C. pecorum infection. Overseas studies for example, have reported reduced growth rates and decreased overall herd performance in asymptomatic infected calves8,9, but no such studies have been reported in lamb flocks overseas or in Australia. This case investigates the impact of naturally acquired C. pecorum infection in a commercial lamb flock in Central Western NSW from marking until finishing.
A sheep producer from the Warren area was followed up after experiencing annual cases of chlamydiosis in their Border Leicester lambs. The owner had used long-acting oxytetracycline antimicrobials in the past, but continued to get infected individuals with arthritis and severe conjunctivitis. Some years were worse than others and it was becoming an economic concern.
Lambs in this study were managed as per normal farm husbandry practices (e.g. marking, feeding, weaning, vaccinations etc.) One hundred and five Border Leicester mixed sex lambs at time of marking (two months of age) were uniquely ear tagged and sampled at bi-monthly intervals until finishing (ten months of age).
Serum and swab samples (e.g. conjunctival, rectal and vaginal) were collected from the lambs at each sampling. Serum samples were analysed for Chlamydia antibodies using the CFT by the State Veterinary Diagnostic Laboratory in NSW. The Chlamydia CFT detects antibodies to the lipopolysaccharide antigen common to all Chlamydiaceae species10. A serum sample was considered positive with a titre of 16 or greater in this study.
At each sampling time point, body weight was recorded and lambs were scored for clinical parameters such as conjunctival colour, ocular discharge and presence of joint and gait abnormalities.
Clinical examination & Chlamydia CFT
Lambs were first sampled at two months of age. This coincided with the producer’s normal yarding for lamb marking. 49% (51/105) of lambs had varying degrees of conjunctival discharge ranging from dry, to serous and purulent. Grass seeds were also present in the conjunctiva of some lambs. No gait or joint abnormalities were detected at two months of age but 12% (13/105) lambs were seropositive via Chlamydia CFT with the remaining lambs seronegative.
At four months of age, conjunctival discharge was still present with 39% of lambs (42/107) affected and joint lesions started to become apparent in the lamb flock with eight lambs demonstrating palpably swollen joints in one or more joints. Surprisingly, at this sampling, only one lamb had a positive titre.
At six months of age, 40% (42/106) of lambs were seropositive with 70% (72/106) of lambs having evidence of varying degrees of conjunctivitis and ten lambs demonstrating one or more palpable swollen joints. The presence of a swollen joint and/or conjunctivitis did not necessarily correspond with a positive Chlamydia CFT result.
Two months later, the seropositivity had doubled to 80% (85/106) in the lamb flock. Conjunctivitis in the flock had declined to 50% (53/106). Interestingly, the joint lesions palpated two months later were not detected at eight months of age.
At the last sampling (ten months of age), seropositivity in the flock had declined to 31% (31/101). Conjunctivitis in the flock remained with 55% of lambs affected. Swollen joints were palpated in four lambs at ten months of age.
Analysis of remaining data and samples collected (vaginal, rectal and conjunctival swabs) for C. pecorum qPCR is still to be analysed.
Based on these preliminary results, the following trends were observed: (i) peak seroconversion occurred at eight months of age; (ii) the presence or absence of clinical signs did not necessarily correspond with antibody titres; and (iii) that lambs appear to be mostly born seronegative. Based on this study, conjunctivitis was consistent throughout the flock across all sampling time points while signs of joint infection (e.g. palpable synovial joint effusions) remained transient. The lambs in this study were weaned at six months of age. It is possible the stress of weaning could have precipitated a spread of chlamydial flock infection and therefore attributed to a rise in Chlamydia antibody titres. Further investigation into understanding the epidemiology of this disease is being investigated throughout the Central West region.
Thank you to Central West LLS District Veterinarians and Biosecurity Officers for their assistance in this project.