Introduction

Viral Arthritis is the classic, but by no means the only, manifestation of reovirus infection of chickens; at least 5 sero-types of virus occur. Morbidity is high but mortality is usually low. Transmission is by faecal contamination, and good both laterally and vertically. Birds remain carriers for over 250 days. The virus is resistant to heat, ether, chloroform, pH and environmental factors. Reoviruses vary markedly in pathogenicity and the tissue damaged. Some can cause other disease syndromes such as early chick mortality and malabsorption syndrome. Some strains have shown severe systemic disease including pericarditis in chickens. Others have caused immunosuppression by damaging the cloacal bursa in ducks.

Signs

• Lameness.
• Low mobility.
• Poor growth.
• Inflammation at hock.
• Swelling of tendon sheaths.
• Unthriftiness.
• Rupture of gastrocnemius tendons.

Post-mortem lesions

• Swelling and inflammation of digital flexor and metatarsal extensor tendon sheaths.
• Foot pad swelling.
• Articular cartilages may be ulcerated.
• Haemorrhage in tissues.
• Fibrosis in chronic cases.

Diagnosis

Diagnosis may be based on the history, lesions, IFA and rising antibody titre. Isolation may be readily achieved in CE yolk sac and CAM and also cell cultures (CE kidney or liver cells). Serology may be by DID, FAT or Elisa. 'Silent' infections (not associated with obvious disease) are common. Differentiate from mycoplasmosis, salmonellosis, Marek's, Pasteurella, erysipelas.

Treatment

None.

Prevention

Vaccination is ideally carried out by administering a live vaccine in rear followed by an inactivated vaccine prior to coming into lay. Most vaccines are based on strain 11/33. Rear birds in all-in/all-out production systems.