Cause

This disease is caused by Mycoplasma synoviae (Ms).

Transmission

The major mode of transmission of Ms is vertical. (through Ms-infected breeder hens). Horizontal transmission is through bird-to-bird contact and by infected equipment, clothing, shoes, egg boxes and other fomites.

Clinical signs and gross lesions

Vary from asymptomatic infection to mild respiratory signs, airsacculitis, synovitis (an inflammatory swelling of the joints of legs and wings) and inflammation of the sternal bursa ("breast blisters").

Creamy exudates in the joints extending into the tendon tissues are indicative of Ms infection. Airsacculitis with frothy to cheesy exudates in the airsacs can be found, especially if secondary infection with E. coli is present.

Diagnosis

Blood serum testing for specific Ms antibodies with Ms antigen and the findings of specific lesions are indicative of Ms infections. Isolation of the causative Ms organisms is definitive for diagnosis.

Differential diagnosis

Staphylococcal arthritis can also cause swollen joints with creamy exudates that sometimes extends into the tendon sheaths. Reovirus infection can also cause swelling of the joints and tendon sheaths, but the exudates is more watery or blood-tinged. Unless secondary Staphylococcus infection is present.

Treatment and control

Ms infections can be treated with antibiotics (e.g. tetracycline, erythromycin, tylosin, tiamulin) with variable degrees of success . However, control of Ms has been largely successful by blood testing of breeder chickens and elimination of positive Ms-reactors.