Chlamydial polyarthritis is an economically important infectious disease that affects sheep, calves, goats, and pigs. Chlamydial polyarthritis is common in feedlot lambs and has a high morbidity but a very low mortality. Clinical signs in all species include fever and lameness. Antimicrobial therapy is effective.
Chlamydial polyarthritis is an infectious disease that affects sheep, calves, goats, and pigs.
Etiology of Chlamydial Polyarthritis in Large Animals
Strains of the causal agent of chlamydial polyarthritis, Chlamydophila (Chlamydia) pecorum (reclassified from Chlamydophila [Chlamydia] psittaci), isolated from affected joints of sheep and calves are identical; however, strain-specific antigens in their cell walls distinguish them from strains that cause abortions in sheep and cattle (see Abortion in Large Animals).
The GI tract is of prime importance in the pathogenesis of chlamydial polyarthritis (see Intestinal Chlamydial Infections). The disease has been reproduced experimentally by oral inoculation. Because chlamydiae can be recovered from the feces of clinically normal calves and lambs, it is most likely the GI tract wherein the host and pathogen stay frequently in balance. If there is a shift in favor of the chlamydiae, then a systemic infection and chlamydemia ensue; the ultimate site of replication is the synovial membrane. The GI tract also has been infected after experimental intra-articular inoculations.
Epidemiology of Chlamydial Polyarthritis in Large Animals
Chlamydial polyarthritis occurs in lambs on range, on farms, and in feedlots. In sheep, chlamydial polyarthritis was first described in Wisconsin, and it has since been recognized in the western US, Australia, and New Zealand. The disease was identified in calves from the US, Australia, and Austria, and in pigs from Austria, Bulgaria, and the US. Incidence of the disease in sheep on range is highest between late summer and early winter. Chlamydial polyarthritis is common in feedlot lambs and has a high morbidity but a very low mortality. In sheep and goats, morbidity may be 5%–75%. Economic loss results from reduced growth rates and treatment costs. The disease affects cattle of all ages, but calves 4–30 days old are affected more severely. Chlamydiae are excreted in the feces and urine and transmitted via ingestion or, in some cases, inhalation.
Clinical Findings of Chlamydial Polyarthritis in Large Animals
In sheep and goats, stiffness, lameness, hyporexia or anorexia, and concurrent conjunctivitis may occur. Affected sheep are depressed and reluctant to move, and they often hesitate to stand and bear weight on one or more limbs; however, they may warm out of stiffness and lameness after forced exercise.
Calves may have fever, are moderately alert, and usually nurse if carried to the dam and supported while suckling. They invariably also have diarrhea, which can be severe. Affected calves assume a hunched position while standing; their joints usually are swollen, and palpation causes pain. Navel involvement and nervous signs are not evident.
Chlamydial polyarthritis has been recognized in both older pigs and young piglets. The affected piglets become febrile and anorectic and may develop nasal catarrh, difficulty breathing, and conjunctivitis. This condition has not been clearly differentiated from other infections that lead to polyserositis and arthritis in pigs.
Lesions
The most striking tissue changes are in the joints. In lambs, enlargement of the joints is not often noticed; in chronic advanced cases, however, the stifle, hock, and elbow joints may be slightly enlarged. In calves, periarticular subcutaneous edema along tendon sheaths and fluid-filled, fluctuating synovial sacs contribute to enlargement of the joints. Most affected joints of lambs or calves contain excessive, grayish-yellow, turbid synovial fluid. Fibrin flakes and plaques in the recesses of the affected joints may adhere firmly to the synovial membranes. Joint capsules are thickened. Articular cartilage is smooth, and erosions or evidence of marginal compensatory changes are not present. Tendon sheaths of severely affected lambs and calves may be distended and contain creamy, grayish-yellow exudate. Surrounding muscles are hyperemic and edematous, with petechiae in their associated fascial planes.
Diagnosis of Chlamydial Polyarthritis in Large Animals
High fever
Reluctance to move because of lameness in one or more joints
History, clinical examination, and pathologic changes in the joints and other organs can be of value in the diagnosis of chlamydial polyarthritis. Cytologic examination of synovial fluids or tissues may reveal chlamydial elementary bodies or cytoplasmic inclusions. Isolation and identification of the causative agent from affected joints confirms the diagnosis. Bacteriologic cultures of affected joints usually yield no growth; however, Escherichia coli or streptococci occasionally may be isolated. If the joints of young calves are arthritic, and if navel lesions are absent, chlamydial polyarthritis should be considered.
Clinical and pathologic features distinguish chlamydial polyarthritis from most other conditions that cause stiffness and lameness in lambs. Lambs with mineral deficiency or osteomalacia usually are not febrile. The abnormal osteogenesis in these two conditions and the distinct lesions of white muscle disease are virtually pathognomonic. In arthritis caused by Erysipelothrix rhusiopathiae, there are deposits on and pitting of articular surfaces, periarticular fibrosis, and osteophyte formation. Laminitis due to bluetongue virus infection can be differentiated clinically and etiologically. Detailed microbiological investigations are required to differentiate chlamydial arthritis from mycoplasmal arthritis.
Treatment and Prevention of Chlamydial Polyarthritis in Large Animals
If begun early, treatment with long-acting penicillin, tetracyclines, or tylosin appears to be beneficial for chlamydial polyarthritis. More advanced lesions do not respond satisfactorily. Feeding chlortetracycline (150–200 mg/day) to affected lambs in feedlots decreases the incidence of chlamydial polyarthritis; however, there are no approved chlortetracycline medicated feeds labeled for lambs in the US. No approved vaccines are available.
Key Points
Chlamydial polyarthritis, caprine arthritis and encephalitis, and mycoplasmal polyarthritis in goats are infectious diseases of small ruminants that cause appreciable economic loss.
Management procedures to decrease or prevent these diseases are helpful in decreasing losses.
For More Information
Baird AN, Pugh DG. Sheep and Goat Medicine. 2nd ed. Elsevier Saunders, 2012.
