Chlamydia pecorum is the causal agent of a range of infectious diseases in livestock. The most economically significant of these diseases is polyarthritis. Molecular evidence suggests that genetically distinct strains of C. pecorum have different pathogenic potentials. Experimental evidence of this relationship is lacking, however, the pathogenesis of C. pecorum-associated polyarthritis otherwise remains unknown.
This study examined the ability of two C. pecorum strains isolated from the joint of a sheep with polyarthritis (IPA) and the brain of a calf with sporadic bovine encephalomyelitis (E58) to induce arthritis in 5 – 6 month old lambs. Animals (n=20) were divided evenly into IPA and E58 infection group and received 107 inclusion forming units (IFU) of C. pecorum either via intra-articular (IA; n=5 per strain) or intravenous route (IV; n=5 per strain). A control group (n=15) received either UV inactivated C. pecorum via IA or IV inoculation or Sucrose Phosphate Glutamate (SPG) by IA. As expected, all IA-inoculated sheep (10/10) infected with viable IPA or E58 strains developed lameness within 24 – 48 hr post-infection (PI). Only three animals (3/5; 60%) from the IPA IV administration group developed lameness, 7 – 9 days PI, which eventually resolved after 3 – 5 days. No evidence of lameness was observed in the E58 IV group or in any control animal. The preliminary results of this work suggest that Chlamydia-associated arthritis can be induced experimentally and that key differences may indeed exist in the pathogenic potential of certain C. pecorum strains.
Further work is now underway to assess bacterial shedding pattern and further pathological differences between infection cohorts. This infection model will be useful to understand the factors influencing chlamydial arthritis in sheep and serve as a valuable tool in the development and evaluation of novel control strategies for this widespread livestock pathogen.